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Endotoxemia Severely Affects Circulation During Normoxia and Asphyxia in Immature Fetal Sheep

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Abstract

Objective:The purpose of the present study was to determine whether endotoxins (lipopolysaccharides, LPS) affect the fetal cardiovascular system in a way likely to cause brain damage.

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... Furthermore, LPS blunted circulatory centralization, resulting in decreased blood flow to the placenta and brain and increased blood flow to the carcass, heart, lungs, and adrenals. 10 On the basis of these and other results, we hypothesized that nitric oxide may mediate LPS-induced peripheral vasodilation and the circulatory decentralization that occurs during fetal hypoxemia. Nitric oxide is produced in large quantities after LPS administration and hence might be involved in the pathway that connects endotoxemia to circulatory failure. ...
... Measurements of cardiac output, organ blood flow distribution, blood gases, pH, glucose, and lactate were in the normal range in both groups of fetuses before hypoxemia. 10,15 We found no significant differences in these measurements between the control group and the L-NAME group (Tables 1 to 4). ...
... This decentralization in turn leads to a severe decrease in oxygen delivery to the brain. 10 The changes in fetal cardiovascular control seen in these experiments were of the same order and magnitude as those we have described previously. 10 Other studies have also described fetal hypertension and bradycardia immediately after L-NAME administration in fetal sheep. ...
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To investigate the role of nitric oxide in the process of circulatory decentralization during fetal hypoxemia. Fifteen sheep with singleton pregnancies were chronically instrumented at 107 days of gestation (term is 147 days). Three days later, 8 of the fetuses received nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide synthesis. Fifteen minutes after L-NAME administration, all 15 fetuses received lipopolysaccharides (LPS) from a strain of Escherichia coli. The 7 fetuses that received LPS only were used as controls. Sixty minutes after LPS was administered, the maternal aorta was occluded for 2 minutes in all fetuses. Organ blood flow and physiological variables were measured at 75 minutes before the start of occlusion (ie, at the time of L-NAME administration to the experimental group), at 1 minute before the start of occlusion, and at 2, 4, and 30 minutes after the start of occlusion. Arterial pH was lower in the L-NAME group than in the control group at 1 minute before and 2 minutes after occlusion. Mean arterial pressure was higher in the L-NAME group than in the control group at 2 and 4 minutes after occlusion. Cardiac output fell in the L-NAME group and was lower than in the control group; the percentage of cardiac output to the cerebrum in the L-NAME group was 35% lower than that in the control group. Throughout the study, placental blood flow decreased by more than 80% in both groups and remained low. Blood flow to the fetal body decreased by 65% in the L-NAME group and was lower than in the control group. Blood flow to the carcass also decreased in the L-NAME group and was 36% of that in the control group. Inhibition of nitric oxide synthesis causes a general vasoconstriction in practically all organs and leads to a reduction in LPS-induced circulatory decentralization. The changes in blood flow distribution in endotoxin-treated fetal sheep seem to be mediated in part by nitric oxide.
... In chronically instrumented fetal sheep (0.7 gestation) intravenous injection of LPS (Escherichia coli; O127:B8, Sigma-Aldrich, Deisenhofen, Germany; 53 Ϯ 3 g per kg fetal body weight; bolus injection over 2 minutes) severely decreased placental blood flow within 1 hour, whereas blood flow to the peripheral organs, eg, to the carcass, increased. 47 During a short period of superimposed asphyxia in utero, there was clear evidence of circulatory decentralization; ie, both placental blood flow and cerebral oxygen delivery were nearly arrested, whereas hyperperfusion of peripheral organs, eg, liver, lungs, gastrointestinal tract, and carcass, occurred ( Figure 2). Because the umbilical and placental vessels lack autonomic innervation, 48 the regulation of umbilical and placental blood flow must depend on circulating or locally released vasoactive substances (for review see 49,50 ). ...
... During endotoxemia there was no increase in blood flow to the brain, although oxygen saturation decreased by 50%. 47 This finding is surprising, because an inverse relationship between cerebral blood flow and arterial oxygen content has been described in term as well as in preterm fetal sheep. 53,54 One possible explanation for this phenomenon may be that the physiologic mechanisms mediating the response of cerebral blood flow to hypoxia are altered by LPS, leading to a loss of cerebral autoregulation. ...
... Furthermore, LPS-treated fetuses suffered from severe hypotension during the recovery period after hypoxia, which was accompanied by a 50% reduction in brain blood flow compared with control fetuses. 47 At mean arterial blood pressures below 25-30 mmHg there is a reduction in cerebral blood flow because of an increasing loss of cerebral autoregulation. This reduction affects the parasagittal region of the cerebrum and the white matter in particular. ...
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There is a growing body of evidence from clinical and epidemiologic studies that in utero exposure to infection plays an important role in the genesis of fetal or neonatal injury leading to cerebral palsy and chronic lung disease. Thus, after chorioamnionitis the incidence of immature neonates with periventricular white matter damage and periventricular or intraventricular hemorrhage is significantly elevated. Recent clinical and experimental data support the hypothesis that a fetal inflammatory response links antenatal infection with brain white matter damage and subsequent motor handicap. A variety of studies support the view that cytokines released during intrauterine infection directly cause injury to the immature brain. In this review, we provide evidence that in utero exposure to bacterial infection can severely alter fetal cardiovascular function, resulting in dysregulation of cerebral blood flow and subsequent hypoxic-ischemic brain injury.
... Cerebral hypoperfusion has been viewed as a principal cause of infection-induced brain injury (3). Although hypotension is commonly associated with infection in human neonates (59) and in fetal animal models of endotoxemia (7,8,10,15,56), it is not clearly associated with cerebral hypoperfusion. Thus ...
... Similarly, in a recent study in premature neonates (63), infection-related white matter injury (WMI) was not related to hypotension or to loss of autoregulation, and presumably not to hypoperfusion. In endotoxin-induced brain injury in immature animals, cerebral perfusion was maintained (7,8,13,15) or even increased (56). Because WMI was found to be induced despite increased cerebral perfusion, it has been suggested that cerebral ischemia is not a main etiological factor in endotoxin-induced injury (56). ...
... Arterial O 2 saturation (Sa O 2 ) is normally low in fetal life and falls further during endotoxemia (7,8,10,15,56). As a consequence, oxygen (O 2 ) transport to the brain may be compromised and neuronal injury may result even if cerebral blood flow (CBF) were to be maintained. Several studies have described falls in cerebral O 2 transport during endotoxemia (7,8), an effect ascribed to the inability of CBF to increase in the face of falling arterial blood pressure and hypoxemia. ...
Article
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We studied the impact of endotoxemia on cerebral blood flow (CBF), cerebral vascular resistance (CVR), and cerebral oxygen transport (O(2) transport) in fetal sheep. We hypothesized that endotoxemia impairs CBF regulation and O(2) transport, exposing the brain to hypoxic-ischemic injury. Responses to lipopolysaccharide (LPS; 1 microg/kg iv on 3 consecutive days, n = 9) or normal saline (n = 5) were studied. Of LPS-treated fetuses, five survived and four died; in surviving fetuses, transient cerebral vasoconstriction at 0.5 h (DeltaCVR approximately +50%) was followed by vasodilatation maximal at 5-6 h (DeltaCVR approximately -50%) when CBF had increased (approximately +60%) despite reduced ABP (approximately -20%). Decreased CVR and increased CBF persisted 24 h post-LPS and the two subsequent LPS infusions. Cerebral O(2) transport was sustained, although arterial O(2) saturation was reduced (P < 0.05). Histological evidence of neuronal injury was found in all surviving LPS-treated fetuses; one experienced grade IV intracranial hemorrhage. Bradykinin-induced cerebral vasodilatation (DeltaCVR approximately -20%, P < 0.05) was abolished after LPS. Fetuses that died post-LPS (n = 4) differed from survivors in three respects: CVR did not fall, CBF did not rise, and O(2) transport fell progressively. In conclusion, endotoxin disrupts the cerebral circulation in two phases: 1) acute vasoconstriction (1 h) and 2) prolonged vasodilatation despite impaired endothelial dilatation (24 h). In surviving fetuses, LPS causes brain injury despite cerebral O(2) transport being maintained by elevated cerebral perfusion; thus sustained O(2) transport does not prevent brain injury in endotoxemia. In contrast, cerebral hypoperfusion and reduced O(2) transport occur in fetuses destined to die, emphasizing the importance of sustaining O(2) transport for survival.
... Several reports describe a rise in lactate and CO 2 values hours after an inflammatory stimulus in fetuses and neonates. 42,[56][57][58] Fetal acidemia might have occurred in response to IA LPS due to a partial reduction in placental perfusion, 42,58 or alterations in the fetal metabolic activity after the inflammatory insult. 57 Fetal Glc and oxygen values were not impaired after IA LPS exposure, due possibly to a maintained nutrient supply to fetal tissues, 57,59 or to an acidemiadependent effect on the fetal hemodynamic response by increasing blood pressure or heart rate demonstrated in other studies. ...
... Several reports describe a rise in lactate and CO 2 values hours after an inflammatory stimulus in fetuses and neonates. 42,[56][57][58] Fetal acidemia might have occurred in response to IA LPS due to a partial reduction in placental perfusion, 42,58 or alterations in the fetal metabolic activity after the inflammatory insult. 57 Fetal Glc and oxygen values were not impaired after IA LPS exposure, due possibly to a maintained nutrient supply to fetal tissues, 57,59 or to an acidemiadependent effect on the fetal hemodynamic response by increasing blood pressure or heart rate demonstrated in other studies. ...
... 57 Fetal Glc and oxygen values were not impaired after IA LPS exposure, due possibly to a maintained nutrient supply to fetal tissues, 57,59 or to an acidemiadependent effect on the fetal hemodynamic response by increasing blood pressure or heart rate demonstrated in other studies. 58,60 Likewise, we found that IA LPS induced the activation of fetal stress responses characterized by an increase in circulating plasma cortisol and norepinephrine. Studies have shown a rise in cortisol and norepinephrine hormone concentrations after LPS administration in adult models of endotoxemia. ...
Article
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Chorioamnionitis is associated with inflammatory end-organ damage in the fetus. Tissues in direct contact with amniotic fluid drive a pro-inflammatory response and contribute to this injury. However, due to a lack of direct contact with the amniotic fluid, the liver contribution to this response has not been fully characterized. Given its role as an immunologic organ, we hypothesized that the fetal liver would demonstrate an early innate immune response to an in utero inflammatory challenge. Fetal sheep (131 ± 1 d gestation) demonstrated metabolic acidosis and high cortisol and norepinephrine values within 5 h of exposure to intra-amniotic LPS. Likewise, expression of pro-inflammatory cytokines increased significantly at 1 and 5 h of exposure. This was associated with NF-κB activation, by inhibitory protein IκBα degradation, and nuclear translocation of NF-κB subunits (p65/p50). Corroborating these findings, LPS exposure significantly increased pro-inflammatory innate immune gene expression in fetal sheep hepatic macrophages in vitro. Thus, an in utero inflammatory challenge induces an early hepatic innate immune response with systemic metabolic and stress responses. Within the fetal liver, hepatic macrophages respond robustly to LPS exposure. Our results demonstrate that the fetal hepatic innate immune response must be considered when developing therapeutic approaches to attenuate end-organ injury associated with in utero inflammation.
... coli; 53 3 g/kg fetales KG) bewirkte bei unreifen Schaffeten einen schweren Abfall der plazentaren Perfusion, während die Durchblutung der peripheren Organe anstieg (Abb. 2) [36]. Daraus resultierte eine Hypoxämie mit Azidämie. ...
... Applikation von LPS (E. coli; 50 g/kg fetales KG) die fetale kardiovaskuläre Funktion während und kurz nach einer intrauterinen Hypoxie zwar beeinflusst, diese Auswirkungen aber gegenüber unreifen Tieren weitaus weniger gravierend waren [36,39] Übersicht Kreislaufzentralisation beeinträchtigt, so dass der Anstieg der Hirndurchblutung im Sauerstoffmangel nicht erfolgte. Im Gegensatz zu den unreifen Tieren waren diese pathophysiologischen Veränderungen weniger ausgeprägt und innerhalb von zwei Stunden reversibel [36,39]. ...
... coli; 50 g/kg fetales KG) die fetale kardiovaskuläre Funktion während und kurz nach einer intrauterinen Hypoxie zwar beeinflusst, diese Auswirkungen aber gegenüber unreifen Tieren weitaus weniger gravierend waren [36,39] Übersicht Kreislaufzentralisation beeinträchtigt, so dass der Anstieg der Hirndurchblutung im Sauerstoffmangel nicht erfolgte. Im Gegensatz zu den unreifen Tieren waren diese pathophysiologischen Veränderungen weniger ausgeprägt und innerhalb von zwei Stunden reversibel [36,39]. ...
Article
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Klinische und epidemiologische Studien weisen auf eine wichtige Rolle perinataler Infektionen in der Genese fetaler und neonataler Schädigungen hin. Eine Chorioamnionitis ist nicht nur von wesentlicher Bedeutung für die Entwicklung einer Frühgeburt, sondern erhöht auch das Risiko perinataler Hirnschäden. Im Vordergrund stehen neben der peri- und intraventrikulären Hirnblutung, insbesondere Läsionen der weißen Hirnsubstanz, die so genannte periventrikuläre Leukomalazie. Diese wird heute als wesentliche Ursache für die spätere Ausbildung einer spastischen Zerebralparese angesehen. Bakterielle Endotoxine und im Körper freigesetzte proinflammatorische Zytokine spielen eine Schlüsselrolle in der Pathogenese der infektionsvermittelten perinatalen Hirnschädigung. Sie verursachen eine schwere Beeinträchtigung der fetalen Herz-Kreislauf-Regulation mit Abfall des zerebralen Sauerstofftransportes, führen zu einer direkten Schädigung der weißen Hirnsubstanz und scheinen das unreife Gehirn gegenüber einer Sauerstoffmangelsituation zu sensibilisieren. Die Aufklärung der pathophysiologischen Mechanismen im Rahmen einer intrauterinen Infektion des Feten könnte entscheidend dazu beitragen, die Inzidenz perinatal erworbener Hirnschäden und somit die Morbidität der betroffenen Kinder zu senken.
... (50 µg/kg fetales KG) das fetale kardiovaskuläre System schwerwiegend vor, während und nach einer kurzen hypoxischen Phase (Garnier 2001) . Wird dem Feten LPS in utero intravenös verabreicht, so folgen fetale Tachykardie, Hypoxämie, Hypotension und erhöhte systemische proinflammatorische Zytokine (Duncan 2002, Seehase 2011 . ...
... Einundzwanzig fetale Schafe wurden in einem mittleren Schwangerschaftsalter von 107 ± 1 Tagen durch einen operativen Eingriff permanent an Überwachungsgeräte angeschlossen (Abbildung 21) (Garnier 2001 ...
Thesis
Eine intrauterine Infektion ist eine ernstzunehmende Erkrankung mit möglicherweise schwerwiegenden Folgen für den Feten. Frühgeborene, die einer Chorioamnionitis ausgesetzt waren, haben jedoch eine geringere Mortalitätsrate mit biochemischen und strukturellen Veränderungen während der Lungenentwicklung. Vorhergehende experimentelle Arbeiten belegen die Initiierung einer Lungenreifung durch intraamniotisch verabreichtes Lipopolysaccharid. Hierbei wurde durch Aspiration der Amnionflüssigkeit eine fetale pulmonale Inflammationsreaktion in Gang gesetzt. Die Hypothese der vorliegenden Arbeit lautete, dass eine durch intravenös appliziertes Lipopolysaccharid induzierte fetale systemische Inflammation die intrauterine Lungenreifung ebenfalls beeinflusst. Die im Rahmen dieser Arbeit durchgeführten Versuche erfolgten an 21 fetalen Schafen mit einem Gestationsalter von 107 Tagen. Alle Tiere wurden zunächst mit intrauterinen Kathetern versehen. Nach einer Erholungsphase von 3 Tagen erhielten die Kontrolltiere (N=12) Kochsalzlösung und die Tiere der Versuchsgruppe (N=9) 100ng Lipopolysaccharid intravenös. Lungenstruktur und Lungenreifung der fetalen Schafe wurden mittels biochemischer und histologischer Untersuchungen nach 3 (N=5) und nach 7 (N=4) Tagen beurteilt. Die Infusion der Lipopolysaccharidlösung hatte zumindest innerhalb des Versuchszeitraums keinen Einfluss auf das Körpergewicht des Feten. Die systemische Entzündung trägt jedoch zu einer pränatalen Verletzung mit strukturellen pulmonalen Veränderungen bei. Sowohl eine Lungenreifung als auch eine gestörte strukturelle Lungenentwicklung traten nach einer kurzfristigen fetalen Inflammation ein. Die Konzentration an Interleukin-6 in der bronchoalveolären Lavage stieg 3 Tage nach Applikation des Lipopolysaccharids mehr als 40fach an. Sowohl die Prozessierung von Pro-Surfactant Protein (SP)-B zu reifem SP-B als auch erhöhte Konzentrationen an SP-B konnten nach 7 Tagen nachgewiesen werden. Ebenfalls war eine Steigerung des phosphorylierten STAT-3 im Lungengewebe zu erkennen. Die Ablagerung von Elastinfasern an Septierungsstellen der Alveolen wurde innerhalb von 3 Tagen nach Lipopolysaccharidapplikation negativ beeinflusst. Aus den Erkenntnissen dieser Arbeit könnten neue Therapieansätze sowohl für das Atemnotsyndrom des Frühgeborenen als auch der bronchopulmonalen Dysplasie resultieren, die eine Modulation der Entzündungsreaktion zum Ziel haben. Alle therapeutischen Ansätze werden einen Weg zwischen den positiven Effekten der Lungenreifung mit gesteigerter Compliance, reduzierter Alveolarwanddicke und vermehrtem prozessiertem SP-B und den schädlichen Einwirkungen auf die Lungenstruktur mit veränderter Elastinverteilung und kapillärer Leckage finden müssen. Bedauerlicherweise können die erhobenen Daten nicht klären, ob die einmalige Infusion von LPS eine anhaltende oder permanente Störung der alveolären Entwicklung hervorbringt. Die strukturellen Veränderungen des Lungengewebes, die denen einer BPD ähneln, lassen jedoch eine permanente Organschädigung befürchten.
... For example, in young adult rats, hypoxia induced 90 min after gram-negative lipopolysaccharide (LPS) infusion synergistically reduced blood pressure and superior mesenteric blood flow (5). Similarly, in preterm fetal sheep, LPS administration 1 h before 2 min of asphyxia, induced by occlusion of the maternal aorta, was associated with impaired peripheral vasoconstriction during asphyxia and a high rate of fetal death compared with saline pretreatment (12). ...
... This finding is in contrast with previous clinical studies of severe sepsis (29,30) and acute LPS injection in animal models (11,23). Similarly, we found no effect of acute on chronic LPS infusion on peripheral vasoconstriction as measured in the femoral vascular bed or on the initial increase in BP, relative to baseline values, in contrast with a previous report of blunted vasoconstriction during occlusion 1 h after LPS injection in the carcass and liver of preterm fetal sheep (12). These differences likely simply reflect that in the previous studies asphyxia was induced around the time of the maximal hemodynamic and biochemical compromise after LPS administration (6, 12) compared with exposure over more than 4 days in this study. ...
Article
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There is increasing evidence that exposure to infection can sensitize the fetus to subsequent hypoxic injury. However, it is unclear whether this involves compromise of the fetal cardiovascular adaptation to acute asphyxia. Chronically instrumented 103 day old (0.7 gestational age, term is 147 days) fetal sheep in utero were randomized to receive either gram-negative lipopolysaccharide (LPS) as a continuous low dose infusion for 120 h plus boluses of 1 µg LPS at 48 h, 72 h and 96 h with asphyxia at 102 h (i.e. 6 h after the final LPS bolus) induced by umbilical cord occlusion for 15 min (LPS-treated, n=8), or the same volume of saline plus occlusion (saline-treated, n=7). Fetuses were killed five days after occlusion. LPS was associated with a more rapid fall in fetal heart rate at the onset of occlusion (P < 0.05), and with minimally lower values during occlusion (P < 0.05). The LPS-treated fetuses had lower fetal mean arterial blood pressure (BP) and greater carotid artery blood flow (CaBF) before occlusion (P < 0.05), but showed an increase in BP and fall in CaBF to similar values as saline controls during occlusion. There were no differences between the groups in femoral blood flow before or during occlusion. Contrary to our initial hypothesis, acute on chronic exposure to LPS was associated with more rapid cardiovascular adaptation to umbilical cord occlusion.
... First, we studied the effects of lipopolysaccharides (LPS) on circulatory responses in chronically instrumented immature fetal sheep before, during, and after 2 min of intrauterine asphyxia [30]. Within 1 h after i.v. ...
... Applying TNFa to the incubation medium for 48 h resulted in a significant Fig. 2. Oxygen delivery to the cerebrum (ml O 2 /min  100 g) in control (n ¼ 6) and LPS treated (n ¼ 7) immature fetal sheep before, during and after arrest of uterine blood flow for 2 min. During the immediate recovery period there was still a severe cut back in delivery of oxygen in fetuses of the study group [30]. Values are given as means AE S:E:M. ...
Article
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Children undergoing perinatal brain injury often suffer from the dramatic consequences of this misfortune for the rest of their lives. Despite the severe clinical and socio-economic significance, no effective clinical strategies have yet been developed to counteract this condition. This review describes the pathophysiological mechanisms that are implicated in perinatal brain injury. These include the acute breakdown of neuronal membrane potential followed by the release of excitatory amino acids such as glutamate and aspartate. Glutamate binds to postsynaptically located glutamate receptors that regulate calcium channels. The resulting calcium influx activates proteases, lipases and endonucleases which in turn destroy the cellular skeleton. The acute lack of cellular energy during ischemia induces almost complete inhibition of cerebral protein biosynthesis. Once the ischemic period is over, protein biosynthesis returns to preischemic levels in non-vulnerable regions of the brain, while in more vulnerable areas it remains inhibited. A second wave of neuronal cell damage occurs during the reperfusion phase induced by the postischemic release of oxygen radicals, synthesis of nitric oxide (NO), inflammatory reactions and an imbalance between the excitatory and inhibitory neurotransmitter systems. Clinical studies have shown that intrauterine infection increases the risk of periventricular white matter damage especially in the immature fetus. This damage may be mediated by cardiovascular effects of endotoxins leading to cerebral hypoperfusion and by activation of apoptotic pathways in oligodendrocyte progenitors through the release of pro-inflammatory cytokines. Knowledge of these pathophysiological mechanisms has enabled scientists to develop new therapeutic strategies which have been shown to be neuroprotective in animal experiments. The potential of such therapies is discussed here, particularly the promising effects of postischemic induction of mild cerebral hypothermia, the application of the calcium-antagonist flunarizine and the administration of magnesium.
... To elucidate the effects of endotoxins on fetal cardiovascular control we applied i.v. LPS to preterm fetal lambs (15). During a short period of superimposed asphyxia, these fetuses were not able to maintain circulatory centralization, i.e. to increase blood flow to the central organs at the expense of the peripheral perfusion. ...
... However, as shown in a recent study on fetal sheep, i.v. application of LPS at a much lower concentration (50 g/kg body wt) severely compromised fetal cardiovascular control and nearly arrested cerebral oxygen delivery shortly after superimposed hypoxia (15). LPS-induced effects on cerebral blood flow therefore cannot be excluded by a single measurement at the end of a hypoxic-ischemic insult. ...
Article
Perinatal brain damage is associated not only with hypoxic-ischemic insults but also with intrauterine inflammation. A combination of antenatal inflammation and asphyxia increases the risk of cerebral palsy >70 times. The aim of the present study was to determine the effect of intracisternal (i.c.) administration of endotoxin [lipopolysaccharides (LPS)] on subsequent hypoxic-ischemic brain damage in neonatal rats. Seven-day-old Wistar rats were subjected to i.c. application of NaCl or LPS (5 microg/pup). One hour later, the left common carotid artery was exposed through a midline neck incision and ligated with 6-0 surgical silk. After another hour of recovery, the pups were subjected to a hypoxic gas mixture (8% oxygen/92% nitrogen) for 60 min. The animals were randomized to four experimental groups: 1) sham control group, left common carotid artery exposed but not ligated (n = 5); 2) LPS group, subjected to i.c. application of LPS (n = 7); 3) hypoxic-ischemic study group, i.c. injection of NaCl and exposure to hypoxia after ligation of the left carotid artery (n = 17); or 4) hypoxic-ischemic/LPS study group, i.c. injection of LPS and exposure to hypoxia after ligation of the left carotid artery (n = 19). Seven days later, neonatal brains were assessed for neuronal cell damage. In a second set of experiments, rat pups received an i.c. injection of LPS (5 microg/pup) and were evaluated for tumor necrosis factor-alpha expression by immunohistochemistry. Neuronal cell damage could not be observed in the sham control or in the LPS group. In the hypoxic-ischemic/LPS group, neuronal injury in the cerebral cortex was significantly higher than in animals that were subjected to hypoxia/ischemia after i.c. application of NaCl. Injecting LPS intracisternally caused a marked expression of tumor necrosis factor-alpha in the leptomeninges. Applying LPS intracisternally sensitizes the immature rat brain to a subsequent hypoxic-ischemic insult.
... Attenuation of responses to repeated LPS exposure has been described previously (34,35), and may be due to down-regulation of the LPS receptor CD14 (36). The fetal hypoxemia and metabolic acidosis after LPS are likely due to placental dysfunction as LPS, albeit at higher doses, increases umbilico-placental vascular resistance (37). It is also possible that placental exchange may have been restricted as a result of placental edema. ...
... The normal response to hypoxemia in the fetus is an increase in cerebral blood flow, which serves to maintain cerebral O 2 delivery (22, 38 -40), although the ability to increase cerebral blood flow through vasodilatation is limited in the immature fetus (41). It has recently been shown that, during the fetal hypoxemia associated with LPS administration in the immature fetus, cerebral blood flow is not increased and cerebral delivery of O 2 is impaired (37,42); the observed fetal hypotension could have contributed to these changes. The absence of increased cerebral blood flow in response to LPS administration is consistent with our observation that there was no increase in the percentage of neuropil occupied by blood vessels in brains of LPS-exposed fetuses. ...
Article
Intrauterine infection has been linked to neurologic injury in preterm infants. However, a reproducible model of white matter injury in the preterm fetus in a long gestation species that can be monitored in utero is currently unavailable. Thus, our objective was to determine the effects of bacterial endotoxin (lipopolysaccharide, LPS) on physiologic and inflammatory responses and brain structure in the preterm ovine fetus. At 0.7 of gestation, six catheterized fetuses received three to five intravenous injections of LPS (1 micro g/kg) over 5 d; seven fetuses served as controls. Fetal responses were monitored and brain tissue examined 10-11 d after the initial LPS injection. After LPS on d 1 and 2, fetuses became transiently hypoxemic and hypotensive and blood IL-6 levels were increased, but these responses were smaller or absent after subsequent LPS exposures. Neural injury was observed in all LPS-exposed fetuses, most prominently in the cerebral white matter. Injury ranged from diffuse subcortical damage to periventricular leukomalacia, and in the brainstem the cross-sectional area of the corticospinal tract was reduced by 30%. Thus, repeated exposure of the preterm ovine fetus to LPS causes neuropathology resembling that of cerebral palsy and provides a robust model for exploring the etiology, prevention, and treatment of white matter damage.
... In addition to fetal inflammation, how-ever, this approach also induces important superimposed hypoxia ischemia. 12 Second, little attention has been paid to other CNS regions besides the cerebral WM. To overcome the first drawback, we studied the sheep CNS pathology after CA by LPS administration into the amniotic fluid. ...
... First, the CA-associated systemic inflammation has been previously characterized in this model by Kramer et al. 13 Second, the IA LPS strategy avoids the superimposed hypoxia ischemia of the IV strategy and the local processes caused by an intracerebral route. 12,27 Third, species with a long gestation duration, such as human beings and sheep, share several aspects of development and function. In addition, the current study not only focused on brain WMD, but it also analyzed the effect of developmental inflammation on both the cerebral cortical and subcortical GM structures and the cerebellar and SC regions. ...
Article
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We quantified the impact of chorioamnionitis on both the white and gray matter structures of the preterm ovine central nervous system (CNS). The CNS was studied at 125 days of gestation, either 2 or 14 days after the intraamniotic administration of 10 mg of lipopolysaccharide (LPS) (Escherichia coli) or saline. Apoptotic cells and cell types were analyzed in the brain, cerebellum, and spinal cord using flow cytometry. Apoptosis and microglial activation increased in all regions with prolonged exposure to LPS-induced chorioamnionitis. Astrocytes were increased in the brain and cerebellum of LPS-exposed fetuses but not in the spinal cord. Mature oligodendrocytes decreased in the cerebral and cerebellar white matter, the cerebral cortex, caudate putamen, and hippocampus 14 days after LPS. Neurons in the cerebral cortex, hippocampus, and substantia nigra were reduced 14 days after LPS. Fetal inflammation globally but differentially affected the CNS depending on the maturational stage of the brain region.
... Such a deleterious effect consequently results in a considerable fall in the umbilico-placental blood flow and a substantial decrease in oxygen delivery to the brain. 11 Gram-negative septicemia or placental infection/colonization is far from regularly associated with adverse neurological outcome in humans, however, the LPS administration in animals is a strong model, compared to the likely more nuanced situation in human pregnancy, to evaluate the effect of the inflammatory injury on brain damage. In this regard, the measurement of brain constituents to monitor the possible effect of LPS administration could be especially useful having the advantage to offer a direct indication of nervous system damage. ...
... The current study provides evidence that in fetal sheep the induction of central nervous system (CNS) injury by LPS administration is associated with a rapid increase of S100B both in fetal and in maternal bloodstream, in absence of maternal brain damage. These findings and the evidence that LPS application in premature fetal sheep severely affects fetal cardiovascular control during normoxia and asphyxia resulting in a substantial decrease in oxygen delivery to the brain 11 and causes periventricular white matter injury 19 suggest that the increase of S100B in LPS-treated preterm fetal sheep is expression of occurring damage in the fetal nervous tissue due to endotoxin administration. The neuropathological findings in the current study correlate well with brain injuries seen in preterm fetuses ...
Article
Full-text available
Intrauterine infection is suggested to cause perinatal brain white matter injury. In the current study, we evaluated whether S100B, a brain damage marker, may be also assessed in maternal bloodstream after white matter injury induced by fetal intravenous application of lypopolisaccharide (LPS) endotoxin. Fourteen fetal sheeps were chronically catheterized at a mean gestational age of 107 days. Three days after surgery, fetuses (n = 7) received 500 ng of LPS or 2 mL 0.9% saline (n = 7) intravenously (IV). Lypopolisaccharide and placebo groups were monitored by continuous hemodynamic data recordings and at 6 predetermined time points (control value; 3, 6, 24, 48, and 72 hours after LPS/placebo administration) blood was drawn for laboratory parameters and S100B assessment. Brain damage was evaluated by light microscopy after Klüver-Barrera staining. Selected areas of the periventricular white matter were also examined by electron microscopy. White matter injury was detected in all LPS-treated fetuses, whereas no abnormalities were seen in control animals or in LPS-treated mothers. Maternal and fetal S100B protein levels were significantly higher in the LPS group than in the control group at all monitoring time points (P < .001). The highest fetal-maternal S100B levels were observed at 3-hour time-point (P < .001). We found that S100B protein is increased in the maternal district in presence of fetal periventricular brain white matter injury induced by endotoxin. The present data offer additional support for S100B assessment in the maternal circulation in pregnancies complicated by intrauterine infection at risk of white matter injury.
... The mechanisms by which LPS affects fetal physiological status are complex [24] , but it is likely that there are major effects on the umbilico-placental vascular bed and the fetal cardiovascular system. In the ovine fetus, it has been reported that LPS increases umbilico-placental resistance [24][25][26] and decreases ventricular output [25] . The umbilico-placental blood flow decreases profoundly at 4-8 h after LPS [24,26] , a time that coincides with the maximal reduction in fetal oxygenation. ...
... The mechanisms by which LPS affects fetal physiological status are complex [24] , but it is likely that there are major effects on the umbilico-placental vascular bed and the fetal cardiovascular system. In the ovine fetus, it has been reported that LPS increases umbilico-placental resistance [24][25][26] and decreases ventricular output [25] . The umbilico-placental blood flow decreases profoundly at 4-8 h after LPS [24,26] , a time that coincides with the maximal reduction in fetal oxygenation. ...
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Lipopolysaccharide (LPS) delivered acutely to the ovine fetus induces cerebral white matter injury and brain inflammation. N-acetyl cysteine (NAC) is potentially neuroprotective as it blocks the production of inflammatory cytokines and increases glutathione levels; however, it is unknown whether NAC affects the physiological status of the fetus already exposed to an inflammatory environment. Our objective was to determine whether NAC influences the physiological effects of LPS exposure in the ovine fetus. Catheterized fetal sheep underwent one of four treatments (saline, n = 6; LPS, n = 6; LPS + NAC, n = 6; NAC, n = 3) on 5 consecutive days from 95 days of gestation (term approximately 147 days). Fetal arterial pressure and heart rate were recorded and blood samples collected. LPS administration resulted in fetal hypoxemia and hypotension; simultaneous treatment with NAC exacerbated these effects and induced polycythemia. NAC treatment alone had no effect on the fetus. In the presence of LPS, NAC compromises fetal physiological status, suggesting that it may not be a suitable antenatal treatment for a fetus with evidence of inflammation.
... To elucidate the effects of endotoxins on fetal cardiovascular control we applied i.v. LPS to preterm fetal lambs (15). During a short period of superimposed asphyxia, these fetuses were not able to maintain circulatory centralization, i.e. to increase blood flow to the central organs at the expense of the peripheral perfusion. ...
... However, as shown in a recent study on fetal sheep, i.v. application of LPS at a much lower concentration (50 g/kg body wt) severely compromised fetal cardiovascular control and nearly arrested cerebral oxygen delivery shortly after superimposed hypoxia (15). LPS-induced effects on cerebral blood flow therefore cannot be excluded by a single measurement at the end of a hypoxic-ischemic insult. ...
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Perinatal brain damage is associated not only with hypoxic-ischemic insults but also with intrauterine inflammation. A combination of antenatal inflammation and asphyxia increases the risk of cerebral palsy >70 times. The aim of the present study was to determine the effect of intracisternal (i.c.) administration of endotoxin [lipopolysaccharides (LPS)] on subsequent hypoxic-ischemic brain damage in neonatal rats. Seven-day-old Wistar rats were subjected to i.c. application of NaCl or LPS (5 microg/pup). One hour later, the left common carotid artery was exposed through a midline neck incision and ligated with 6-0 surgical silk. After another hour of recovery, the pups were subjected to a hypoxic gas mixture (8% oxygen/92% nitrogen) for 60 min. The animals were randomized to four experimental groups: 1) sham control group, left common carotid artery exposed but not ligated (n = 5); 2) LPS group, subjected to i.c. application of LPS (n = 7); 3) hypoxic-ischemic study group, i.c. injection of NaCl and exposure to hypoxia after ligation of the left carotid artery (n = 17); or 4) hypoxic-ischemic/LPS study group, i.c. injection of LPS and exposure to hypoxia after ligation of the left carotid artery (n = 19). Seven days later, neonatal brains were assessed for neuronal cell damage. In a second set of experiments, rat pups received an i.c. injection of LPS (5 microg/pup) and were evaluated for tumor necrosis factor-alpha expression by immunohistochemistry. Neuronal cell damage could not be observed in the sham control or in the LPS group. In the hypoxic-ischemic/LPS group, neuronal injury in the cerebral cortex was significantly higher than in animals that were subjected to hypoxia/ischemia after i.c. application of NaCl. Injecting LPS intracisternally caused a marked expression of tumor necrosis factor-alpha in the leptomeninges. Applying LPS intracisternally sensitizes the immature rat brain to a subsequent hypoxic-ischemic insult.
... [3][4][5] Elevated pro-inflammatory cytokines also alter the permeability of the fetal blood-brain barrier and important mediators of fetal blood flow, nitric oxide and endothelin-1, rendering the neonate susceptible to further brain injury from relatively minor episodes of hypoxia-ischemia (HI). [6][7][8][9] In the fetus exposed to chorioamnionitis, white and gray matter brain injury may result from a combination of changes in cerebral blood flow (CBF) and as a direct result of inflammation, 10 with long-term consequences of periventricular leukomalacia, cerebral palsy and cognitive deficits. 2,[11][12][13] A meta-analysis of preterm and term infants showed increased risks of 80 to 140% for cerebral palsy if exposed to histological or clinical chorioamnionitis (CC). ...
... Fetal sheep without inflammation were able to rapidly recover CBF by shifting blood flow to protect the brain, whereas those with inflammation were unable to fully respond when a secondary HI insult occurred. 6,23,24 In the face of a global HI insult, the fetal animal will divert blood from cortical areas to protect deep brain structures that are more metabolically active and at greater risk of significant injury. [25][26][27] Differential blood flow between white matter, cortical gray matter and deep gray nuclei has been shown in term asphyxiated infants within 1 to 6 days of life. ...
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Objective: Sex is an important determinant of neonatal outcomes and may have a significant role in the physiologic response to maternal chorioamnionitis. Our goal was to determine cerebral blood flow (CBF) parameters by sex and subsequent neurodevelopment in healthy term infants exposed to chorioamnionitis. Study Design: CBF by Doppler ultrasound in anterior and middle cerebral (ACA, MCA) and basilar arteries were analyzed for time-averaged maximum velocity (TAMX) and corrected resistive index in 52 term control and chorioamnionitis-exposed infants between 24 and 72 h after birth. Placental pathology confirmed histologic evidence of chorioamnionitis (HC). Bayley Scales of Infant Development-III were administered at 12 months. Result: HC male infants had significantly greater TAMX in the MCA and lower mean MCA and ACA resistance than HC females. Abnormal CBF correlated negatively with neurodevelopmental outcome. Conclusion: CBF is altered in term infants with histologically confirmed chorioamnionitis compared with control infants with sex-specific differences.
... fetale Inflammation häufig durch intraamniale oder intravenöse Applikation von Lipopolysacchariden (LPS) induziert. In Untersuchungen der eigenen Arbeitsgruppe ließ sich eine infektionsvermittelte plazentare Minderperfusion mit chronischer Hypoxämie ohne Azidämie nachweisen [57]. Im weiteren Verlauf entwickelte sich eine pulmonale Hyperperfusion und ein Abfall des zerebralen Sauerstofftransportes. ...
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Die bakterielle Infektion von Chorion und Amnion (Chorioamnionitis) ist bei Frühgeborenen häufig nachweisbar. Dabei entwickelt die Mutter selten Symptome einer systemischen Inflammationsreaktion, sodass die Chorioamnionitis häufig asymptomatisch und chronisch verläuft. Hiervon ist die fetale Inflammationsreaktion (FIRS, fetal inflammatory response syndrome) mit dem Nachweis einer umbilikalen Entzündungsreaktion bzw. erhöhten Serumspiegeln von proinflammatorischen Zytokinen zu trennen. In klinischen und experimentellen Studien wurde die systemische fetale Inflammationsreaktion als wichtiger Risikofaktor für eine schlechte pulmonale und neurologische Entwicklung der überlebenden, extrem unreifen Frühgeborenen determiniert. Interessanterweise ist jedoch das Vorliegen einer Chorioamnionitis mit einer verminderten neonatalen Mortalität extrem unreifer Frühgeborener assoziiert. In dem vorliegenden Übersichtsreferat wird der aktuelle Kenntnisstand zur Pathogenese der inflammationsassoziierten perinatalen Morbidität mit besonderer Berücksichtigung von pulmonalen und neurologischen Krankheitsbildern dargestellt und das Konzept einer fetalen Multiorganerkrankung während intrauteriner Infektion diskutiert.
... Cerebral hypoperfusion is a potential damaging mechanism as hypotension is commonly associated with infection in preterm neonates (Seri and Noori 2005) and in fetal animal models of endotoxemia (Garnier et al. 2001;Duncan et al. 2002;Dalitz et al. 2003;Peebles et al. 2003;Coumans et al. 2005). As the regulation of the cerebral circulation in conditions such as hypotension is different in the fetus and newborn (Volpe 2008), a critical difference in their relative circulatory responses might be anticipated. ...
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As the comparative pathophysiology of perinatal infection in the fetus and newborn is uncertain, this study contrasted the cerebral effects of endotoxemia in conscious fetal sheep and newborn lambs. Responses to intravenous bacterial endotoxin (lipopolysaccharide, LPS) or normal saline were studied on three consecutive days in fetal sheep (LPS 1 μg/kg, n = 5; normal saline n = 5) and newborn lambs (LPS 2 μg/kg, n = 10; normal saline n = 5). Cerebro‐vascular function was assessed by monitoring cerebral blood flow (CBF) and cerebral vascular resistance (CVR) over 12 h each day, and inflammatory responses were assessed by plasma TNF alpha (TNF‐α), nitrate and nitrite concentrations. Brain injury was quantified by counting both resting and active macrophages in the caudate nucleus and periventricular white matter (PVWM). An acute cerebral vasoconstriction (within 1 h of LPS injection) occurred in both the fetus (ΔCVR +53%) and newborn (ΔCVR +63%); subsequently prolonged cerebral vasodilatation occurred in the fetus (ΔCVR −33%) in association with double plasma nitrate/nitrite concentrations, but not in the newborn. Abundant infiltration of activated macrophages was observed in both CN and PVWM at each age, with the extent being 2–3 times greater in the fetus (P < 0.001). In conclusion, while the fetus and newborn experience a similar acute disruption of the cerebral circulation after LPS, the fetus suffers a more prolonged circulatory disruption, a greater infiltration of activated macrophages, and an exaggerated susceptibility to brain injury. Though the fetus and newborn experience a similar acute disruption of the cerebral circulation in endotoxaemia, the fetus suffers a more prolonged circulatory disruption, a higher plasma nitric oxide production, a greater infiltration of activated macrophages, and an exaggerated susceptibility to brain injury. The differences will shed light on further research and target interventions in perinatal infection.
... A partial list would include placental hormones, whose production is inhibited by LPS (Okada et al., 1997), and prostaglandins (Bennett et al., 2000) and nitric oxide and/or peroxynitrite (Athanassakis et al., 1999), whose productions are oppositely increased. It is worthwhile to mention that, along with the increase in nitric oxide, LPS may also severely reduce placental blood flow; resulting in considerable cerebral damage (Garnier et al., 2001). ...
Article
Prenatal infection constitutes an important risk factor for brain injury, in both premature and full-term infants. Unfortunately, as the mechanisms involved are far from understood, no therapeutic strategy emerges to prevent the damage. We tested the hypothesis that administration of lipopolysaccharide (LPS) to gravid female rats enhanced glutamate-induced oxidative stress in brain of pups. A microdialysis probe was implanted into the striatum of 14-day-old animals and the release of hydroxyl radicals (.OH) in the perfusion medium was evaluated. Glutamate promoted a delayed.OH release in the offspring of dams given LPS, contrasting with the.OH decreases observed in control animals. A similar response occurred after infusion of (R,S)-3,5-dihydroxyphenylglycine (DHPG), a Group I metabotropic glutamate receptor (mGluR) agonist. This response was not consecutive to a remote activation of N-methyl-D-aspartate (NMDA) receptors, as it was unaffected by an NMDA receptor antagonist. Furthermore, the response to NMDA itself decreased in the offspring of dams given LPS. Massive amounts of DHPG, however, likely internalizing the mGlu receptor, still blunted the response to NMDA, as in controls. No quantitative variation occurred in mGluR1, mGluR5, or the NR1 subunit of the NMDA receptor between controls and neonates born from LPS-treated dams. Direct LPS injection into age-matched pups, by contrast, affected the response to neither glutamate nor DHPG. These results confirm that normally during perinatal development, the brain is protected from any oxidative stress resulting from excess glutamate, and the results support the hypothesis that maternal infection before delivery may lead to critical brain damage via the release of toxic free radicals.
... As seen in neonatal models, in the sheep fetus the fetal adaptive responses to asphyxia are also influenced by the timing between the exposure to LPS and asphyxia, albeit very few antenatal studies have been performed. Asphyxia induced by a short uterine artery occlusion an hour after an LPS bolus impaired the acute fetal cardiovascular adaptations of 0.75 gestation fetal sheep (Garnier et al. 2001). In contrast, asphyxia J Physiol 595.6 induced by 15 min of UCO after 5 days of chronic infusion with superimposed boluses of LPS enhanced the responses of 0.7 gestation fetal sheep, despite baseline hypotension and vasodilatation (Fig. 7) . ...
Article
Premature fetuses and babies are at greater risk of mortality and morbidity than their term counterparts. The underlying causes are multifactorial, but include exposure to hypoxia. Immaturity of organs and their functional control may impair the physiological defence responses to hypoxia and the preterm fetal responses, or lack thereof, to moderate hypoxia appear to support this concept. However, as this review demonstrates, despite immaturity, the preterm fetus responds to asphyxia in a qualitatively similar manner to that seen at term. This highlights the importance in understanding metabolism versus homeostatic threat when assessing fetal responses to adverse challenges such as hypoxia. Data are presented to show that the preterm fetal adaptation to asphyxia is triphasic in nature. Phase one represents the rapid institution of maximal defences, designed to maintain blood pressure and central perfusion at the expense of peripheral organs. Phase two is one of adaptive compensation. Controlled reperfusion partially offsets peripheral tissue oxygen debt, while maintaining sufficient vasoconstriction to limit the fall in perfusion. Phase three is about decompensation. Strikingly, the preterm fetus generally performs better during phases two and three, and can survive for longer without injury. Paradoxically, however, the ability to survive can lead to longer exposure to hypotension and hypoperfusion and thus potentially greater injury. The effect of fetal sex, inflammation and drugs on the triphasic adaptations is reviewed. Finally, the review highlights the need for more comprehensive studies to understand the complexity of perinatal physiology if we are to develop effective strategies to improve preterm outcomes. This article is protected by copyright. All rights reserved.
... Acute, High-Dose Exposure to LPS Conceptually, acute systemic injection of LPS corresponds broadly with acute, rapidly progressive sepsis. Multiple studies have shown that fetal sheep exposed to acute boluses of Gram-negative LPS commonly develop white matter damage [63][64][65][66][67][68][69][70][71] . Typically, such large doses are associated with acute loss of a third to over 40% of fetuses associated with terminal hypotension [64,67,72] , similar to the deaths of 6/11 fetuses in a recent report [73] . ...
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One of the central, unanswered questions in perinatology is why preterm infants continue to have such poor long-term neurodevelopmental, cognitive and learning outcomes, even though severe brain injury is now rare. There is now strong clinical evidence that one factor underlying disability may be infection, as well as nonspecific inflammation, during fetal and early postnatal life. In this review, we examine the experimental evidence linking both acute and chronic infection/inflammation with perinatal brain injury and consider key experimental determinants, including the microglia response, relative brain and immune maturity and the pattern of exposure to infection. We highlight the importance of the origin and derivation of the bacterial cell wall component lipopolysaccharide. Such experimental paradigms are essential to determine the precise time course of the inflammatory reaction and to design targeted neuroprotective strategies to protect the perinatal brain from infection and inflammation. © 2015 S. Karger AG, Basel.
... Consistent with this, surviving fetuses also developed tachycardia, in parallel with delayed hypotension (4). Thus the mechanism of profound hypotension is likely a combination of impaired cardiac contractility with systemic vasodilation and reduced placental perfusion (9,17). The findings in the present study, and previously, of increased carotid blood flow despite hypotension are consistent with marked fetal vasodilation (15,31). ...
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Introduction. Acute, high-dose exposure to endotoxin lipopolysaccharide (LPS) in preterm fetal sheep can trigger periventricular white matter lesions (PVL), in association with severe hypotension/hypoxemia and significant mortality. Intriguingly, however, chronic or repeated exposure to LPS can induce tachyphylaxis. We therefore tested the hypothesis that progressive, acute on chronic fetal infection would be associated with white matter injury with little fetal mortality. Methods. Chronically instrumented preterm (0.7 gestational age) fetal sheep were exposed to a continuous low dose LPS infusion (100 ng over 24 h, followed by 250 ng/24 h for 96 h) or saline. Boluses of 1 μg LPS or saline were given at 48 h, 72 h and 96 h; sheep were killed at day 10. Results. 6 of 11 fetal sheep exposed to saline infusion + LPS boluses died 4-7 h after the first bolus. In contrast, there was no fetal mortality after saline infusions alone (n=9), low-dose LPS infusion + saline boluses (n=5) or low-dose LPS + LPS boluses (n=9). Low-dose LPS infusion + LPS boluses was associated with greater microglial induction than low-dose LPS + saline boluses, but a similar area of periventricular white matter inflammation. One fetus developed severe focal white matter necrosis after LPS infusion + boluses. Conclusions. The acute cardiovascular compromise associated with high-dose, acute exposure to LPS is markedly attenuated by previous low-dose infusions, with limited apparent exacerbation of periventricular white matter injury compared with low-dose infusion alone.
... There are few data available in large animals. In preterm fetal sheep, highdose LPS (50 μg/kg) given one hour before occlusion of the maternal aorta for two minutes impaired circulatory centralization and cerebral oxygen delivery, with increased mortality [16]. It is striking though, that these studies have all involved single boluses of LPS. ...
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Background Perinatal asphyxia and exposure to intrauterine infection are associated with impaired neurodevelopment in preterm infants. Acute exposure to non-injurious infection and/or inflammation can either protect or sensitize the brain to subsequent hypoxia-ischemia. However, the effects of subacute infection and/or inflammation are unclear. In this study we tested the hypothesis that acute-on-chronic exposure to lipopolysaccharide (LPS) would exacerbate white matter injury after subsequent asphyxia in preterm fetal sheep. Methods Fetal sheep at 0.7 gestational age received a continuous LPS infusion at 100 ng/kg for 24 hours, then 250 ng/kg/24 hours for 96 hours, plus 1 μg boluses of LPS at 48, 72, and 96 hours or the same volume of saline. Four hours after the last bolus, complete umbilical cord occlusion or sham occlusion was induced for 15 minutes. Sheep were sacrificed 10 days after the start of infusions. Results LPS exposure was associated with induction of microglia and astrocytes and loss of total and immature and mature oligodendrocytes (n = 9) compared to sham controls (n = 9). Umbilical cord occlusion with saline infusions was associated with induction of microglia, astrogliosis, and loss of immature and mature oligodendrocytes (n = 9). LPS exposure before asphyxia (n = 8) was associated with significantly reduced microglial activation and astrogliosis and improved numbers of immature and mature oligodendrocytes compared to either LPS exposure or asphyxia alone. Conclusions Contrary to our initial hypothesis, the combination of acute-on-chronic LPS with subsequent asphyxia reduced neuroinflammation and white matter injury compared with either intervention alone.
... An ascending infection causes a so-called "fetal inflammatory response syndrome" [33]. The release of endotoxins associated with this syndrome leads to serious impediment of the fetal cardiovascular system regulation, resulting in a reduction in cerebral blood circulation and thus in ischemic lesions in the white brain matter [34,35]. Cytokines, glutamate, and free radicals are also able to directly damage oligodendrocytes in the early stages of development and thus also disrupt the subsequent myelinisation process, which can significantly affect the development of an infant's motor skills [36][37][38] (Figure 3). ...
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Preterm infants born before the 30th week of pregnancy are especially at risk of perinatal brain damage which is usually a result of cerebral ischemia or an ascending intrauterine infection. Prevention of preterm birth and early intervention given signs of imminent intrauterine infection can reduce the incidence of perinatal cerebral injury. It has been shown that administering magnesium intravenously to women at imminent risk of a preterm birth leads to a significant reduction in the likelihood of the infant developing cerebral palsy and motor skill dysfunction. It has also been demonstrated that delayed clamping of the umbilical cord after birth reduces the rate of brain hemorrhage among preterm infants by up to 50%. In addition, mesenchymal stem cells seem to have significant neuroprotective potential in animal experiments, as they increase the rate of regeneration of the damaged cerebral area. Clinical tests of these types of therapeutic intervention measures appear to be imminent. In the last trimester of pregnancy, the serum concentrations of estradiol and progesterone increase significantly. Preterm infants are removed abruptly from this estradiol and progesterone rich environment. It has been demonstrated in animal experiments that estradiol and progesterone protect the immature brain from hypoxic-ischemic lesions. However, this neuroprotective strategy has unfortunately not yet been subject to sufficient clinical investigation.
... Studies of placental pathology following preterm birth have suggested that chronic placental infection may alter placental vascular structure, but this may not be sufficient to impair fetal oxygenation ( Salafia et al., 1995). In contrast, acute intrauterine infections may adversely affect placental function leading to fetal hypoxemia and even hypoxic fetal death ( Dalitz et al., 2003;Garnier et al., 2001). Indeed the placenta itself may be a key factor in the etiology of perinatal brain damage, since it has inflammatory reactions to bacterial and viral infection. ...
Article
A compromised intrauterine environment that delivers low levels of oxygen and/or nutrients, or is infected or inflammatory, can result in fetal brain injury, abnormal brain development and in cases of chronic compromise, intrauterine growth restriction. Preterm birth can also be associated with injury to the developing brain and affect the normal trajectory of brain growth. This review will focus on the effects that episodes of perinatal hypoxia (acute, chronic, associated with inflammation or as an antecedent of preterm birth) can have on the developing brain. In animal models of these conditions we have found that relatively brief (acute) periods of fetal hypoxemia can have significant effects on the fetal brain, for example death of susceptible neuronal populations (cerebellum, hippocampus, cortex) and cerebral white matter damage. Chronic placental insufficiency which includes fetal hypoxemia, nutrient restriction and altered endocrine status can result in fetal growth restriction and long-term deficits in neural connectivity in addition to altered postnatal function, for example in the auditory and visual systems. Maternal/fetal inflammation can result in fetal brain damage, particularly but not exclusively in the white matter; injury is more pronounced when associated with fetal hypoxemia. In the baboon, in which the normal trajectory of growth is affected by preterm birth, there is a direct correlation between a higher flux in oxygen saturation and a greater extent of neuropathological damage. Currently, the only established therapy for neonatal encephalopathy in full term neonates is moderate hypothermia although this only offers some protection to moderately but not severely affected brains. There is no accepted therapy for injured preterm brains. Consequently the search for more efficacious treatments continues; we discuss neuroprotective agents (erythropoietin, N-acetyl cysteine, melatonin, creatine, neurosteroids) which we have trialed in appropriate animal models. The possibility of combining hypothermia with such agents or growth factors is now being considered. A deeper understanding of causal pathways in brain injury is essential for the development of efficacious strategies for neuroprotection.
... In pregnant ewes, intravenous administration of LPS induced placental hypoperfusion, causing chronic hypoxemia, moderate acidemia and cardiotocography changes. 89,90 Subsequently, a pulmonary hyperperfusion and a decrease in cerebral oxygen transport developed. The latter correlated with an inflammatory reaction of the subcortical regions and periventricular white matter similar to that observed in premature newborns below 1500 g birth weight after intrauterine infection. ...
Article
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The bacterial infection of chorion and amnion is a common finding in premature delivery and is referred to as chorioamnionitis. As the mother rarely shows symptoms of a systemic inflammation, the course of chorioamnionitis is frequently asymptomatic and chronic. In contrast, the fetal inflammatory response syndrome represents a separate phenomenon, including umbilical inflammation and increased serum levels of proinflammatory cytokines in the fetus. Ascending maternal infections frequently lead to systemic fetal inflammatory reaction. Clinical studies have shown that antenatal exposure to inflammation puts the extremely immature neonates at a high risk for worsening pulmonary, neurological and other organ development. Interestingly, the presence of chorioamnionitis is associated with a lower rate of neonatal mortality in extremely immature newborns. In the following review, the pathogeneses of inflammation-associated perinatal morbidity are outlined. The concept of fetal multiorganic disease during intrauterine infection is introduced and discussed.
... Quantitative EEG measurements for each waveform band were performed by automated analysis techniques, and each band is presented as a percentage of total power. This technique used the following range of frequencies: delta (0 -3.9 Hz), theta (4 -7.9 Hz), alpha (8 -12.9 Hz), and beta (13)(14)(15)(16)(17)(18)(19)(20)(21)(22). This involved calculating power spectra (by fast Fourier transform) of the EEG on sequential epochs, using a 10-s Hanning window to minimize spectral leakage (29). ...
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Exposure to chorioamnionitis is strongly associated with neurodevelopmental disability after premature birth; however, it remains unclear whether subclinical infection affects functional EEG maturation. Chronically instrumented 103-104-day-old (0.7 gestational age: term 147 days) fetal sheep in utero were randomized to receive either gram-negative LPS by continuous low-dose infusion (100 ng iv over 24 h, followed by 250 ng/24 h for 4 days; n = 6) or the same volume of normal saline (n = 9). Arterial plasma cortisol, ACTH, and IL-6 were measured. The delta (0-3.9 Hz), theta (4-7.9 Hz), alpha (8-12.9 Hz), and beta (13-22 Hz) components of the EEG were determined by power spectral analysis. Brains were taken after 10 days for histopathology. There were no changes in blood gases, cardiovascular variables, or EEG power during LPS infusion, but a transient rise in plasma cortisol and IL-6 (P < 0.05). LPS infusion was associated with loss of the maturational increase to higher frequency activity, with reduced alpha and beta power, and greater delta power than saline controls from 6 to 10 days (P < 0.05). Histologically, LPS was associated with increased numbers of microglia and TNF-α-positive cells in the periventricular white matter and frontoparietal cortex, increased caspase-3-positive cells in white matter, but no loss of CNPase-positive oligodendrocytes, Nurr-1 subplate cells, or gyral complexity. These data suggest that low-dose endotoxin exposure can impair EEG maturation in preterm fetal sheep in association with neural inflammation but without hemodynamic disturbances or cortical injury.
... Neben einer zytotoxischen Wirkung von bakteriellen Endotoxinen und proinflammatorischen Zytokinen auf das fetale Gehirn ist die Infektions-assoziierte Einschränkung der fetalen Herz-Kreislauf-Regulation für die perinatale Morbidität von wesentlicher Bedeutung [14]. Eine intrauterine fetale Inflammationsantwort kann durch intraamniale bzw. ...
Article
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Seit Jahrzehnten unverändert sind spontane vorzeitige Wehentätigkeit und Frühgeburtlichkeit von zentraler Bedeutung für perinatale Morbidität und Mortalität in den westlichen Industrienationen. Im Vergleich zu Reifgeborenen tragen Frühgeborene ein 40fach erhöhtes neonatales Mortalitätsrisiko. Somit ist die Frühgeburtlichkeit für 70 % der neonatalen Mortalität und 50 % der neurologischen Langzeitmorbidität verantwortlich [[1]]. Hierbei stellt die vorzeitige Wehentätigkeit und Frühgeburt die Endstrecke unterschiedlicher ätiologischer Risikofaktoren und Auslöser dar. Dies impliziert, dass durch monozentrische Ansätze immer nur ein Teilaspekt der Problematik Frühgeburtlichkeit bearbeitet werden kann. Es ist an der Zeit das Symptom Frühgeburt als eine syndromale Erkrankung anzuerkennen, die nur die Endstrecke unterschiedlicher und häufig gemeinsam auftretender pathophysiologischer Mechanismen darstellt. In den letzten Jahren hat sich herausgestellt, dass genitale und intrauterine Infektionen zu den bedeutsamen Risikofaktoren für die Entwicklung von vorzeitiger Wehentätigkeit und Frühgeburt zählen [[2]]. In großen Studienkollektiven sind aszendierende genitale Infektionen in 40 % der Fälle von Frühgeburtlichkeit nachweisbar. Daraus entwickelte sich die Hoffnung, die Problematik Frühgeburtlichkeit bald durch großzügigen Einsatz von Antibiotika lösen zu können. Allerdings haben die großen Interventionsstudien der letzten Jahre widersprüchliche Ergebnisse gezeigt. Es wird deutlich, dass zahlreiche pathophysiologische Mechanismen im Rahmen der vorzeitigen Wehentätigkeit und Frühgeburtlichkeit zum Zeitpunkt des Infektionsnachweises bereits irreversibel induziert sind und somit eine antibiotische Therapie diese Kaskaden nicht mehr unterdrücken kann. Wird eine lokale Dysbiose bzw. beginnende genitale infektion frühzeitig erkannt, so belegt mittlerweile eine stetig steigende Zahl von prospektiv randomisierten Studien einen Benefit der Interventionsgruppen. Die Hypothese der infektiologischen Genese eines Großteils der spontanen vorzeitigen Wehentätigkeit und Frühgeburtlichkeit wird somit unterstützt. Darüber hinaus häufen sich Berichte, dass genetische Faktoren eine Überempfindlichkeit gegenüber antenatalen Infektionen mit inadäquater Inflammationsreaktion vermitteln und somit eine Risikosteigerung für eine Frühgeburtlichkeit darstellen [[3]]. Diese so genannten Gen-Umwelt-Interaktionen sind seit Jahren für das Verständnis komplexer Krankheitsbilder, wie Atherosklerose, Adipositas, Hypertonus, Depression etc. beschrieben. In der vorliegenden Übersichtsarbeit wird der Stellenwert antenataler Infektionen in der Pathogenese der Frühgeburtlichkeit unter besonderer Berücksichtigung prädisponierender genetischer Faktoren diskutiert.
Article
In most cases of neonatal hypoxic-ischemic encephalopathy, the exact timing of the hypoxic-ischemic event is unknown, and we have few reliable biomarkers to precisely identify the phase of injury or recovery in an individual patient. However, it is becoming increasingly clear that for neuroprotection in neonates to succeed, an understanding of the phase of injury is important to ascertain. In addition, in utero antecedents of chronic hypoxia, hypoxic preconditioning, intrauterine infection, and fetal gender may change the expected time course of injury. Neuroprotective interventions, such as hypothermia and N-acetylcysteine, currently have efficacy in human and animal studies only if instituted early in the inflammatory cascade. Although these cascades are currently being investigated, molecular mechanisms of recovery have received little attention and may ultimately reveal a window for therapeutic intervention that is much longer than current paradigms.
Article
Endotoxin causes hypoxemia and white matter injury in the preterm ovine fetus. Because cerebral hypoxia could contribute to brain injury, our objective was to determine the effects of endotoxin on regional cerebral oxygen (O(2)) delivery. To investigate causes of fetal hypoxemia, we also measured placental blood flow. We administered endotoxin (lipopolysaccharide, LPS) at 1 microgram/kg (intravenously) to 11 catheterized fetal sheep at approximately 0.7 of term; controls (n = 7) received saline. We measured fetal cerebral blood flow (CBF) and placental blood flow using microspheres, arterial blood gases, arterial pressure, and heart rate. Seven fetuses survived LPS administration (LPS-S) and four died. LPS-S fetuses were hypoxemic at 4-8 hours after LPS. Fetal hemoglobin concentration and hematocrit increased by about 14% at 4 hours after LPS exposure, and mean arterial pressure decreased significantly from 4-8 hours. After LPS, CBF did not change significantly, but total cerebral O(2) delivery decreased by 35.7% at 4 hours and by 28.3% at 8 hours. O(2) delivery to cerebral white matter decreased below pre-LPS values at 4 hours (-35.9%) and 8 hours (-28.6%) after LPS. Relative to pre-LPS values, placental blood flow decreased by 53.3% at 4 hours and 43.0% at 8 hours after LPS. Immature fetal sheep exposed to LPS had profound reductions in placental blood flow and cerebral O(2) delivery, which could contribute to fetal brain injury. Reduced O(2) delivery to white matter was similar to that in other brain regions. Mechanisms that enable fetal CBF to increase in hypoxemic conditions were apparently ineffective in the presence of LPS.
Article
Children who suffer from perinatal brain injury often deal with the dramatic consequences of this misfortune for the rest of their lives. Despite the severe clinical and socioeconomic significance, no effective clinical strategies have yet been developed to counteract this condition. As shown in recent studies, perinatal brain injury is usually brought about by cerebral ischemia, cerebral hemorrhage, or an ascending intrauterine infection. This review focuses on the pathophysiologic pathways activated by these insults and describes neuroprotective strategies that can be derived from these mechanisms. Fetal cerebral ischemia causes an acute breakdown of neuronal membrane potential followed by the release of excitatory amino acids such as glutamate and aspartate. Glutamate binds to postsynaptically located glutamate receptors that regulate calcium channels. The resulting calcium influx activates proteases, lipases, and endonucleases, which in turn destroy the cellular skeleton. A second wave of neuronal cell damage occurs during the reperfusion phase. This cell damage is thought to be caused by the postischemic release of oxygen radicals, synthesis of nitric oxide, inflammatory reactions, and an imbalance between the excitatory and inhibitory neurotransmitter systems. Furthermore, secondary neuronal cell damage may be brought about in part by induction of a cellular suicide program known as apoptosis. Recent studies have shown that inflammatory reactions not only aggravate secondary neuronal damage after cerebral ischemia, but may also injure the immature brain directly. This damage may be mediated by cardiovascular effects of endotoxins leading to cerebral hypoperfusion and by activation of apoptotic pathways in oligodendrocyte progenitors through the release of proinflammatory cytokines. Periventricular or intraventricular hemorrhage (PIVH) is a typical lesion of the immature brain. The inability of preterm fetuses to redistribute cardiac output in favor of the central organs and their lack of cerebral autoregulation may cause significant fluctuations in cerebral blood flow when oxygen is in short supply. Disruption of the thin-walled blood vessels in the germinal matrix with subsequent cerebral hemorrhage is often the inevitable result and is at times associated with cerebral hemorrhagic infarction. Knowledge of these pathophysiologic mechanisms has enabled scientists do develop new therapeutic strategies, which have been shown to be neuroprotective in animal experiments. The potential of such therapies is discussed here, particularly the promising effects of postischemic induction of cerebral hypothermia, the application of the calcium-antagonist flunarizine, and the administration of magnesium.
Article
Objective:Our aim was to determine the acute physiologic effects of intra-amniotic endotoxin administration in fetal sheep, and in particular, to determine whether intra-amniotic endotoxin causes an increase in fetal cortisol that could underlie the functional maturation of the fetal lungs previously reported in this model.
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In the present study we examined the effects of low-dose endotoxin (lipopolysaccharides, LPS) on continuously recorded umbilical blood flow. Twenty fetal sheep were catheterized at a gestational age of 107 +/- 1 days. A flow probe was placed around either the common umbilical artery or one single umbilical artery. Three days later fetuses received either 100 or 500 nanograms of LPS (n = 14) or 2 mL saline (n = 6) intravenously. Six fetuses died within 12 hours after LPS. Fetal heart rate (FHR), mean arterial pressure (MAP), and umbilical blood flow (Q(umb)) were monitored for 3 days. FHR increased by 25 +/- 4% at 4-5 hours after LPS (P <.01) and was elevated for 15 hours after LPS. MAP increased by 18 +/- 5% 1 hour after LPS (P <.01) and returned to control value 4-5 hours after LPS. Q(umb) began to decrease 1 hour after LPS and was minimal (-30 +/- 7%, P <.001) at 4-5 hours after LPS. Q(umb) slowly returned to the control value at 12 hours after LPS. Placental vascular resistance increased by 73 +/- 37% (P <.01), whereas pH did not appreciably change. Intravenous application of endotoxin caused a substantial and long-lasting decrease in umbilical blood flow resulting in fetal hypoxemia without acidemia. These effects may be of significance in the development of fetal brain damage associated with intrauterine infection.
Article
There is strong evidence from recent clinical studies that ascending intrauterine infection is associated with an increased incidence of periventricular leukomalacia in very premature fetuses. Periventricular leukomalacia is characterized by disrupted myelination from a loss of oligodendrocyte progenitors. We investigated the effects of proinflammatory cytokines on the survival and differentiation of this cell type. Cultures of more than 90% A2B5-positive progenitors were prepared from neonatal rats and kept for 3 days in medium supplemented with factors that stimulate cell proliferation. After 1 day in proliferation medium, cells were treated with interferon-gamma (100 U/mL) and tumor necrosis factor-alpha (100 ng/mL) for 48 hours triggering an increase in apoptotic A2B5 progenitor cells from 3.2 +/- 2.3% to 11.0 +/- 2.6%. After cytokine treatment cultures were transferred to medium containing factors to promote differentiation of progenitors into the myelinating phenotype. In cytokine pretreated cultures, only 2.6 +/- 1.1% of total cells survived after a total of 9 days in vitro, whereas in untreated cultures most cells differentiated as shown by expression of myelin basic protein, myelin-associated glycoprotein, 2,3-cyclic nucleotide 3-phosphodiesterase, and myelin oligodendrocyte-specific protein. Using ten-fold reduced concentrations of combined interferon-gamma (10 U/mL) and tumor necrosis factor-alpha (10 ng/mL) pretreatment resulted in a survival to 11.2 +/- 4.9% of total cells with 36.3 +/- 11.6% A2B5-positive cells at day 9. This indicates a major enrichment of undifferentiated cells compared with untreated controls which harbored only 1.0 +/- 0.3% A2B5-positive cells. Inflammatory cytokines not only induced apoptotic cell death but also prevented the differentiation of immature A2B5 oligodendrocyte progenitors into the myelinating phenotype.
Article
Abnormal development of the brain during fetal life is now thought to contribute to the aetiology of many functional and behavioural disorders that manifest throughout life. Many factors are likely to underlie such abnormal development including genetic makeup and an adverse intrauterine environment. This review will focus on prenatal hypoxic-ischemic injury and inflammatory/infective insults. A range of experimental models have been used to characterise lesions formed in response to these insults and to determine mechanisms of damage resulting from such events. Relatively brief periods of fetal hypoxia result in neuronal death (cerebellum, hippocampus, and cerebral cortex), white matter damage and reduced growth of neural processes. These effects are more profound at mid than late gestation. Chronic mild placental insufficiency can result in fetal growth restriction and deficits in neural connectivity and myelination. Exposure of the preterm fetus to inflammatory agents causes brain damage particularly in the white matter and this is exacerbated by hypoxia. These studies show that the timing, severity and nature of specific insults are critical in determining the pattern of injury and thus the extent to which neurological function will be affected postnatally. Defining the causes, patterns and mechanisms of brain injury is crucial if we are to develop rational neuroprotective strategies to reduce the burden of altered brain growth and poor functional and behavioural outcomes.
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31. Kedda MA, Duffy DL, Bradley B, O'Hehir RE, Thompson PJ.ADAM33 haplotypes are associated with asthma in a largeAustralian population. Eur J Hum Genet. 2006;14:1027-36.32. Foley SC, Mogas AK, Olivenstein R, Fiset PO, Chakir J,Bourbeau J, et al. Increased expression of ADAM33 and ADAM8with disease progression in asthma. J Allergy Clin Immunol.2007;119:863-71.33. Raby BA, Silverman EK, Kwiatkowski DJ, Lange C, Lazarus R,Weiss ST.ADAM33polymorphismsandphenotypeassociationsinchildhoodasthma.JAllergyClinImmunol.2004;113:1071-8.34. Chen C, Huang X, Sheppard D. ADAM33 is not essential forgrowthanddevelopmentanddoesnotmodulateallergicasthmain mice. Mol Cell Biol. 2006;26:6950-6.35. Schedel M, Depner M, Schoen C, Weiland SK, Vogelberg C,Niggemann B, et al. The role of polymorphisms in ADAM33, adisintegrinandmetalloprotease33,inchildhoodasthmaandlungfunction in two German populations. Respir Res. 2006;7:91.
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We examined the effect of graded reduction in uterine blood flow on distribution of cardiac output and oxygen delivery to fetal organs and venous blood flow patterns in 9 fetal sheep using the radionuclide-labeled microsphere technique. We reduced uterine blood flow in two steps, decreasing fetal oxygen delivery to 70% and 50% of normal, and compared the results with those from a similar study from our laboratory on graded umbilical cord compression. With 50% reduction in fetal oxygen delivery, blood flow and the fraction of the cardiac output distributed to the brain, heart, and adrenal gland increased and that to the lungs, carcass, skin, and scalp decreased. Oxygen delivery to the brain and myocardium was maintained, while that to the adrenal doubled, and that to the brain stem increased transiently. The decrease in oxygen delivery to both carcass and lower body segment correlated linearly with oxygen consumption (P less than 0.001). The proportion of umbilical venous blood passing through the ductus venosus increased from 44.6% to 53% (P less than 0.05). The preferential distribution of ductus venosus blood flow through the foramen ovale to the heart and brain increased, but that to the upper carcass decreased so that ductus venosus-derived blood flow to the upper body did not change. Hence, the oxygen delivered to the brain from the ductus venosus was maintained, and that to the heart increased 54% even though ductus venosus-derived oxygen delivery to the upper body fell 34%. Abdominal inferior vena caval blood flow and its contribution to cardiac output decreased, but the proportion of the abdominal inferior vena caval blood distributed through the foramen ovale also increased from 23.0 to 30.9%. However, the actual amount of inferior vena caval blood passing through the foramen ovale did not change. There was a 70% fall in oxygen delivery to the upper body segment from the inferior vena cava. A greater portion of superior vena caval blood was also shunted through the foramen ovale to the upper body, but the actual amounts of blood and oxygen delivered to the upper body from this source were small. Thus, graded reduction of uterine blood flow causes a redistribution of fetal oxygen delivery and of venous flow patterns, which is clearly different from that observed previously during graded umbilical cord occlusion.
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The knowledge on fetal and neonatal circulatory physiology accumulated by basic scientists and clinicians over the years has contributed considerably to the recent decline of perinatal morbidity and mortality. This review will summarize the peculiarities of the fetal circulation, the distribution of organ blood flow during normoxemia, and that during oxygen lack caused by various experimental perturbations. Furthermore, the relation between oxygen delivery and tissue metabolism during oxygen lack as well as evidence to support a new concept will be presented along with the principal cardiovascular mechanisms involved. Finally, blood flow and oxygen delivery to the principal fetal organs will be examined and discussed in relation to organ function. The fetal circulatory response to hypoxemia and asphyxia is a centralization of blood flow in favour of the brain, heart, and adrenals and at the expense of almost all peripheral organs, particularly of the lungs, carcass, skin and scalp. This response is qualitatively similar but quantitatively different under various experimental conditions. However, at the nadir of severe acute asphyxia the circulatory centralization cannot be maintained. Then there is circulatory decentralization, and the fetus will experience severe brain damage if not expire unless immediate resuscitation occurs. Future work in this field will have to concentrate on the important questions, what factors determine this collapse of circulatory compensating mechanisms in the fetus, how does it relate to neuronal damage, and how can the fetal brain be pharmacologically protected against the adverse effects of asphyxia.
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The effects of acute asphyxia on both the time course of blood flow changes in central and peripheral organs, including the skin, and the time course of changes in oxygen consumption were studied in 9 unanaesthetized fetal sheep in utero at 130 +/- 2 days of gestation during 4-min arrest of uterine blood flow. Blood flow distribution and total oxygen consumption were determined at 1-min intervals during asphyxia using isotope-labelled microspheres (15 micrometer diameter) and by calculating the decline of the arterial O2 content, respectively. During asphyxia peripheral blood flow including that to the skin, scalp, and choroid plexus decreased rapidly, whereas blood flow to the heart, brain stem and (in surviving fetuses only) adrenals increased slowly. Total oxygen consumption fell exponentially with time and was closely correlated with the fall in both arterial oxygen content and peripheral blood flow; the time courses of these changes were very similar to those of the decreasing blood flows to the skin and scalp. Blood flow within the brain was redistributed at the expense of the cerebrum and the choroid plexus; the total blood flow to the brain did not change. In the 5 fetuses that died during the recovery period adrenal blood flow failed to increase and, at the nadir of asphyxia, peripheral vessels dilated and central vessels constricted. We conclude that in fetal sheep near term during acute asphyxia the time course of changes in blood flow to central and peripheral organs is different; total oxygen consumption depends on arterial O2 content and peripheral blood flow; total blood flow to the brain does not change, but is redistributed towards the brain stem at the expense of the cerebrum and choroid plexus; fetal death is preceded by a failure of adrenal blood flow to increase, by peripheral vasodilatation, and by central vasoconstriction and skin blood flow validly indicates rapid changes in the distribution of blood flow and the changes in oxygen consumption that accompany it.
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Asphyxia is one of the major causes for fetal brain damage. Although the quality of life of the so affected children is mostly very limited, the pathogenesis of hypoxic fetal brain damage is poorly understood. Particularly, there is a lack of studies, in which cerebral oxygen delivery is directly correlated to the extent of neuronal cell damage in the same brain specimens. Therefore, we measured cerebral oxygen delivery before (- 1 h), during (+3 min & +27 min) and after (+10 min, +4 h, +72 h) 30 min of ischaemia in 5 chronically catheterized normoxemic fetal sheep at 129 +/- 1 days gestation (term is at 147 days) using the microsphere method. In contrast to previous studies (Williams et al. 1990), we arrested carotid arterial blood flow above the lingual artery for 30 min during surgery. Seventy-two hours later the fetal brains were fixed in vivo under barbiturate anaesthesia of both the fetus and the ewe. After cerebral blood flow analysis neuronal cell damage was assessed with light microscopy in 43 specimens of the fetal brain after cresyl violet/fuchsin staining using a scoring system. After arrest of carotid arterial blood flow cerebral blood flow was reduced by 80%. Neuronal cell damage was focussed on the cerebral cortex. Almost no damage could be detected in deeper parts of the brain. In the cerebrum there was threshold oxygen delivery of 3 ml O2/100 g tissue/min, below which neuronal damage occurred. However, there was no correlation between cerebral oxygen delivery and neuronal cell damage in specimens of the cerebrum, in which oxygen delivery was less than 3 ml O2/100 g tissue/min, suggesting selective vulnerability. Therefore, in addition to the reduction in cerebral oxygen delivery, other variables, e.g. neurotransmitter release, receptor pattern or oxygen radicals, may be involved in the development of brain damage.
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We launched a prospective cranial ultrasound study at the Department of Obstetrics and Gynaecology of the University of Giessen. In this study we examined the incidence and severity of brain damage in neonates and related them to various obstetrical risk factors. More than 90% of all neonates born between 1984 and 1988 were included in the study (n = 5286) and were screened by ultrasound for cerebral abnormalities on 5-8 days post-partum. The relation between the incidence of peri/intraventricular haemorrhages (PIVH) and obstetrical risk factors were analyzed by contingency tables. The most frequent abnormality was PIVH (3.6%) of various degrees (grade I-III). Periventricular leucomalacia, porencephalia, subarachnoidal haemorrhages, and hydrocephali were rare (< or = 0.2%). The incidence of PIVH increased progressively with decreasing gestational age, e.g. from 1.6% at 38-43 weeks up to 50.0% at 24-30 weeks of gestation. A large percentage of babies with PIVH were clinically normal. In immature neonates there was a close inverse relationship between Apgar score at 1, 5 and 10 min and both incidence and severity of PIVH. This was in contrast to findings in mature neonates where a marked increase in the incidence of PIVH was found only with Apgar scores as low as 0-4 points. The relation between the incidence of PIVH and both cardiotocography and arterial cord blood pH was poor, independent of the gestational age. The incidence of PIVH was increased in growth retarded fetuses (pH < or = 7.29), premature rupture of membranes, fever sub partu and gestosis. It is interesting to note that in mature fetuses there was no difference in the incidence of PIVH between vaginally delivered (0.8%) and sectioned breech presentations (2.1%). In preterms at 35-37 weeks with prolonged labour and secondary cesarean section, the incidence of PIVH was very high (11.2%). From the present study we conclude that the incidence of PIVH especially in immature neonates is highly associated with low Apgar scores at birth. Since the Apgar score reflects the clinical condition and the degree of circulatory centralisation of neonates that is influenced by various ante- and intranatal risk factors, a protective obstetrical management is necessary to reduce the incidence of PIVH in neonates.
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The aim of the present study was to clarify whether endotoxins [lipopolysaccharides (LPS)] have a toxic effect on fetal brain tissue after cerebral ischemia, while excluding their effect on the cardiovascular system. Experiments were therefore performed on hippocampal slices prepared from mature fetal guinea pigs. In particular, we studied the influence of LPS on nitric oxide production, energy metabolism, and protein synthesis after oxygen-glucose deprivation (OGD). Incubating hippocampal slices in LPS (4 mg/L) for as long as 12 h did not alter cGMP tissue concentrations significantly. However, 10 min after OGD of 40-min duration, cGMP tissue concentrations were substantially increased in relation to controls, and this increase was almost completely blocked by the application of 100 microM N:(omega)-nitro-L-arginine, indicating that nitric oxide synthase was activated after OGD in fetal brain tissue. Again, LPS did not have any effect on cGMP tissue concentrations after OGD. Furthermore, addition of LPS altered neither protein synthesis nor energy metabolism measured 12 h after OGD. We therefore conclude that, apart from their well-known influence on the cardiovascular system, LPS do not alter metabolic disturbances in hippocampal slices of fetal guinea pigs 12 h after OGD. A direct toxic effect of LPS on immature brain tissue within this interval does not therefore seem to be very likely. However, delayed activation of LPS-sensitive pathways that may be involved in cell death, or damage limited to a small subgroup of cells such as oligodendrocyte progenitors, cannot be fully excluded.
Article
The response of the uteroplacental and fetal circulations and oxygen transfer to injection of E. coli endotoxin into the pregnant sheep was investigated. Endotoxin injection into the mother was comprised of three distinct phases: First came a precipitous fall in arterial pressure and uteroplacental blood flow with an increase in uteroplacental vascular resistance. This phase was followed by a progressive recovery period during which flow, pressure, and resistance returned to control values. A third phase occurred during which arterial pressure and uteroplacental blood flow decreased until death of the animal. Despite the marked changes in uteroplacental hemodynamics and a decrease in uteroplacental oxygen transfer, the fetal circulation did not show any major alteration until the terminal phase of shock, when arterial pressure and umbilical flow decreased. There was a fall in fetal oxygen content difference.
Article
The effects of E. coli endotoxin upon fetal, immediate neonatal, and newborn (10 to 20 days) lamb circulation were studied. The fetus and immediate neonate tolerated doses 10 times greater than those proving lethal in adult pregnant sheep without exhibiting obvious signs of circulatory shock; arterial pressure, cardiac output, and vascular resistance were not significantly altered by these large doses. After 10 to 20 days of extrauterine life, the newborn lamb responded in a manner quite similar to the pregnant ewe; a biphasic acute response occurred after endotoxin injection followed by a slow decline in pressure and cardiac output until the termination of the experiment. We believe that the smaller response of the fetus and early neonate to endotoxin may be related not only to the presence of vascular shunts but also to a poorly developed adrenergic system.
Conference Paper
A prospective sonographic study on the incidence of cerebral hemorrhage in 2781 babies born in our unit between 1984 and 1986 revealed that maternal signs of infection during parturition (temperature >38°C) are associated with a high risk for the newborns to develop peri- or intraventricular hemorrhages (Jensen et al. 1992). Since most of these infections are caused by gram-negative bacteria that produce endotoxin, we wished to determine whether endotoxin affects both blood flow and oxygen delivery to the fetal brain and whether it interferes with circulatory centralization during asphyxia.
Article
The release and pharmacokinetics of endothelin-1 (ET-1) in plasma were studied in pigs and humans in vivo. Between 50-90% of plasma ET-1-like immunoreactivity (LI) was cleared by the pig and human kidney, splanchnic circulation, and skeletal muscle. The precursor big ET-1 was only cleared to a moderate extent (34%) by the kidney with progressive formation of ET-1-LI in the pig. The half-lives of circulating ET-1-LI and big ET-1-LI were about 1 and 10 min, respectively. The threshold vasoconstrictor effects for plasma ET-1-LI in the splanchnic and renal circulation in humans were around 30 pM. ET-1-LI in fetal umbilical arterial plasma was very high (15 pM before and 94 pM after establishment of breathing) compared with about 2 pM in maternal plasma. Bacterial endotoxin or sepsis increased ET-1-LI in plasma more than fivefold in both pigs and humans reaching levels close to threshold vasoconstriction. However, hemorrhagic shock or hypotension did not alter plasma ET-1-LI. It is concluded that ET-1 has a short half-life with very high regional plasma clearance, which limits detection of overflow into the systemic circulation. However, release of ET-1 reaching vasoconstrictor levels seems to occur both upon special physiological circulatory changes in the newborn and in septic shock.
Article
In order to determine the relative roles of O2 tension and content, CO2 tension, hydrogen ion concentration, arterial blood pressure, and cardiac output in the regulation of fetal cerebral blood flow (CBF), we used radioactively labeled microspheres to measure flow to 20 major brain regions in 24 chronically catheterized fetal lambs. We continually monitored fetal heart rate and blood pressure, and periodically measured arterial Po2, Pco2, pH, and hematocrit. In addition to CBF measurements during control periods, we measured CBF during: 1) hypoxia (O2 content < 6 ml·dl-1; O2 tension < 15 torr) induced by having the ewe breathe a gas mixture with low O2 concentration, 2) hypercapnia (Pco2 > 50 torr) induced by increasing the maternal inspired CO2, 3) acidosis and alkalosis (7.60 > pH > 6.60) induced by infusing lactic acid or bicarbonate into the fetus, and 4) hypotension (blood pressure < 35 mm Hg) and hypertension (blood pressure > 55 mm Hg) induced by rapidly phlebotomizing or transfusing the fetus. We used multiple regression analysis and analysis of covariance to examine the dependence of total cerebral blood flow on arterial O2 tension and content, CO2 tension, pH, blood pressure, and cardiac output. The results demonstrated that 1) fetal CBF increased linearly as oxygen tension or content decreased and a hierarchy of responsivity occurred (brainstem > subcortex and cortex), 2) fetal CBF increased as carbon dioxide tension increased with a different hierarchy of responsivity (brainstem > subcortex > cortex), and 3) autoregulation of fetal CBF over a wide range of blood pressure or cardiac output was maintained for both total CBF and the various brain regions examined.
Article
The dramatic improvement in neonatal care during the last decade did not succeed in reducing the incidence of periventricular leukomalacia (PVL), suggesting that prenatal events may be the main target for PVL prevention. The studied cohort included 753 very preterm infants born between 24 and 32 weeks of gestational age, admitted to the intensive care unit and surviving at least 7 days; 69 (9.2%) of these infants had a diagnosis of cystic PVL. The highest PVL frequency was observed among the infants born at 28 weeks of gestation (16%). Inflammatory prenatal events occurring during the last days or weeks before delivery and PVL occurrence are strongly correlated. Indeed, the combination of intra-uterine infection and premature rupture of membranes is associated with a very high risk (22%). Prolongation of pregnancy with tocolysis for more than 24 hours also carries a significant 8% risk of PVL. In contrast, chronic fetal distress of long duration, such as severe intra-uterine growth retardation and pre-eclampsia, is seldom followed by PVL (< 2% risk). Similarly, rapid unexpected deliveries entail a minimal PVL risk (4%). Experimental and epidemiological confirmations of these data would have an influence on the management of both the preterm onset of labour and the premature rupture of membranes.
Article
When appropriately and correctly applied, the microsphere technique is relatively simple and extremely accurate. Distribution patterns, both of total systemic arterial blood flow or venous return as well as within specific organs, can be measured. Several techniques have been applied to quantitate flow using microspheres; the reference sample method is extremely simple and by far the most accurate of all. Collection of venous effluent is perhaps more accurate but requires extensive surgery and is almost certainly the least physiologic. Other methods used for quantitation, such as bolus injections of indocyanine green dye or in fusions of diffusable indicators, are considerably less accurate and therefore significantly reduce the reliability of the microsphere technique. Selection of the appropriate size microspheres allows for definition of arteriovenous anastomoses as well as the measurement of organ blood flows and distribution of blood flow within those organs. In most instances, smaller microspheres (15mu diameter or 8-10mu diameter) have significant advantages over larger ones. They are distributed more like red cells, obstruct less of the vascular bed, are less variable in size, and can be given in significantly greater numbers. This latter point is important, since the statistical criteria need to be satisfied and the use of small spheres allows for the more reliable measurement of blood flow to small organs or to small regions of organs.
Article
Neurohistochemical techniques were used to determine the distribution of adrenergic and cholinergic nerves in the human placenta and the umbilical cord adjacent to the chorion. These morphologic studies demonstrate the absence of neural elements in these sites. The significance of these findings to the placental innervation controversy is discussed.
1. Detection of ET-LI in porcine and human tissues in the present study revealed the presence of high levels in blood vessels, heart, airways, kidney, placenta, amnion and umbilical vessels. ET-1 was the predominant form in both porcine and human tissues, while evidence for additional occurrence of ET-3 was obtained in the porcine kidney and spinal cord. No evidence for presence of VIC or ET-2 was obtained in the studied porcine or human tissues. Immunohistochemical techniques revealed the presence of ET-LI in the amniotic membrane cells as well as in vascular endothelial cells. 2. Transient release of ET-LI from the porcine spleen was observed during endotoxin infusion and after a 2 min period of asphyxia. During endotoxin administration plasma ET-LI increased progressively and the presence of both ET-1 and big ET-1 in the plasma was shown. Short term sympatho-adrenal activation did not evoke ET-release, however. In man, high levels of ET-LI, indicating release, were observed in the amniotic fluid and umbilical plasma at birth. 3. Specific, high affinity ET receptors were demonstrated in human and porcine tissues. One main characteristic for ET binding was the extremely slow dissociation rate. The ET-1 selective ETA receptor was predominant in the porcine spleen and renal artery as well as in the human heart and umbilical arteries, whereas the ETB receptor predominated in the porcine renal medulla and the spinal cord and the human placenta. In the porcine and human lung a mixed population of ETA and ETB receptors seemed to be present. ET-1 but not ET-3 increased IP turnover in the spleen, while both ET-1 and ET-3 was effective in the lung, suggesting the same second messenger system for both receptor subtypes. Neither ET-1 nor ET-3 was observed to have any effect on the adenylate cyclase system. 4. ET-1 was extremely potent as a vasoconstrictor in the porcine kidney and spleen in vivo, while the effect in the femoral vascular bed was less pronounced. ET-3 was considerably less potent than ET-1 as vasoconstrictor in the kidney and the spleen. However, ET-1 and ET-3 acted equipotently as vasodilators in the bronchial circulation, suggesting opposite vascular effects in the different vascular beds. Big ET-1 caused only minor vasoconstriction. ET-1 was a potent constrictor agent of human coronary, pulmonary and umbilical vessels as well as of human bronchi in vitro.(ABSTRACT TRUNCATED AT 400 WORDS)
Article
Endothelin-like immunoreactivity was observed in the endothelial lining of umbilical vein and artery as well as in the epithelium of the amniotic membrane. High levels of endothelin-like immunoreactivity (0.4-1.4 pmol g-1) were detected in human amniotic membrane, umbilical vessels and placenta. The concentration of endothelin-like immunoreactivity in the amniotic fluid was much higher (77 pmol l-1) than in umbilical cord plasma (10 pmol l-1). Characterization by reverse phase HPLC revealed that most of the endothelin-like immunoreactivity eluted in the position of synthetic endothelin-1 or oxidized endothelin-1. Specific, high affinity binding sites for endothelin-1 were present in placenta and umbilical artery. Endothelin binding sites were also found in cultured smooth muscle cells from the umbilical artery and vein. In the placenta, endothelin-1 and -3 were almost equipotent as competing ligands for endothelin-1 binding sites, whereas in the umbilical artery endothelin-3 was much less potent than endothelin-1. Scatchard analysis of the binding for placental membranes displayed a straight line (r = -0.994) indicating a single class of endothelin receptors with a Kd-value of 80 pmol l-1 and Bmax of 113 fmol mg-1. Endothelin-1 caused potent contractions of umbilical arteries and veins with threshold effects at 10 pmol l-1 while endothelin-3 had no contractile effect up to 10(-7) mol l-1. It is concluded that endothelin-1 predominates over other endothelins in umbilical vessels, amnion and placenta, and high levels of endothelin-1 was observed in foetal circulation and amniotic fluid. Endothelin-receptors seem to be of different types in placenta (ETB type) and umbilical vessels (ETA type).
Article
The release and pharmacokinetics of endothelin-1 (ET-1) in plasma were studied in pigs and humans in vivo. Between 50-90% of plasma ET-1-like immunoreactivity (LI) was cleared by the pig and human kidney, splanchnic circulation, and skeletal muscle. The precursor big ET-1 was only cleared to a moderate extent (34%) by the kidney with progressive formation of ET-1-LI in the pig. The half-lives of circulating ET-1-LI and big ET-1-LI were about 1 and 10 min, respectively. The threshold vasoconstrictor effects for plasma ET-1-LI in the splanchnic and renal circulation in humans were around 30 pM. ET-1-LI in fetal umbilical arterial plasma was very high (15 pM before and 94 pM after establishment of breathing) compared with about 2 pM in maternal plasma. Bacterial endotoxin or sepsis increased ET-1-LI in plasma more than fivefold in both pigs and humans reaching levels close to threshold vasoconstriction. However, hemorrhagic shock or hypotension did not alter plasma ET-1-LI. It is concluded that ET-1 has a short half-life with very high regional plasma clearance, which limits detection of overflow into the systemic circulation. However, release of ET-1 reaching vasoconstrictor levels seems to occur both upon special physiological circulatory changes in the newborn and in septic shock.
Article
The immune system produces cytokines and other humoral factors to protect the host when threatened by inflammatory agents, microbial invasion, or injury. In some cases this complex defense network successfully restores normal homeostasis, but at other times the overproduction of immunoregulatory mediators may actually prove deleterious to the host. Some examples of immune system-mediated injury have been extensively investigated including anaphylactic shock, autoimmune disease, and immune complex disorders. More recently it has become clear that the cytokine cachectin/tumor necrosis factor (TNF) occupies a key role in the pathophysiology associated with diverse inflammatory states and other serious illnesses including septic shock and cachexia. For example, when cachectin/TNF is produced by resident macrophages during early microbial infection, it mediates an inflammatory response that may alienate and repel the attacking organisms. If the infection spreads, however, the subsequent release of large quantities of cachectin/TNF into the circulation may be catastrophic and trigger a state of lethal shock. These toxic effects occur by direct action of TNF on host cells and by the interaction with a cascade of other endogenous mediators including interleukin-1 and interferon-gamma. The biology of cachectin/TNF will be reviewed, along with the potential for modulating the effects of this pluripotent molecule in a variety of pathologic states.
Article
This study was designed to examine the effects of fetal hypertension on the umbilical artery pulsatility index. Fetal arterial blood pressure and umbilical venous pressure were measured in eight sheep, 3 to 5 days after surgery. Umbilical blood flow was measured with an electromagnetic flowmeter around the common umbilical vein. Umbilical artery flow velocity waveforms were obtained either by an indwelling 5 MHz pulsed Doppler device (n = 4) or transcutaneously by a 4 MHz continuous-wave Doppler device (n = 4). Fetal blood pressure was raised by intravenous infusion of norepinephrine 10 micrograms/min during 5 minutes. Norepinephrine infusion resulted in elevated arterial and umbilical venous pressures, accompanied by a bradycardia during the first 3 minutes. Umbilical blood flow, calculated placental vascular resistance, and umbilical artery pulsatility index did not change. After atropine administration, the norepinephrine-induced elevated arterial and umbilical venous pressures were accompanied by tachycardia, increased umbilical blood flow, and no change in placental vascular resistance and umbilical artery pulsatility index. It is concluded that fetal arterial hypertension provoked by norepinephrine infusion has no effect on placental vascular resistance, umbilical blood flow, and umbilical artery pulsatility index.
Article
Acute fetal hypoxemia increases the vascular resistance of the umbilical veins as well as that of the liver. Because, at least in the human, the umbilical-placental circulation has no autonomic innervation, circulating hormones could well be responsible for this increase in umbilical-placental outflow resistance. In chronically instrumented fetal sheep, norepinephrine, epinephrine, vasopressin, and angiotensin II were infused in sequentially increasing doses into the descending aorta and vascular resistance to umbilical-placental blood flow was measured. Norepinephrine and epinephrine increased the vascular resistance of the umbilical veins in a dose-dependent manner. Both catecholamines also increased the vascular resistance of the liver, resulting in an increase in ductus venosus blood flow. In contrast, vasopressin and angiotensin II had no effect on umbilical-placental outflow resistance. Thus catecholamines may be responsible for the increase in the vascular resistance of the umbilical veins and liver in response to acute fetal hypoxemia.
Article
We used the radionuclide microsphere technique in nine fetal lambs to examine the effect of partial cord compression on distribution of cardiac output and O2 delivery to fetal organs and venous flow patterns. With a 50% reduction in umbilical blood flow the fraction of fetal cardiac output distributed to the brain, heart, carcass, kidneys, and gastrointestinal tract increased. Pulmonary blood flow fell. O2 delivery to the brain and myocardium was maintained but was reduced to peripheral, renal, and gastrointestinal circulations. Hepatic blood flow decreased and O2 delivery fell by 75%. The proportion of umbilical venous blood passing through the ductus venosus increased from 43.9 to 71.8%. The preferential distribution of ductus venosus blood flow through the foramen ovale was enhanced (29.4 vs. 47.2%) and the proportion of O2 delivery to upper body organs derived from the ductus venosus increased (33.2 vs. 49.4%). Abdominal inferior vena caval blood flow increased, and it was also preferentially distributed through the foramen ovale (21.9 vs. 44.2%) and constituted the major fraction of the arterial blood supply to the upper body organs (16.5 vs. 36.4%). Thus cord compression modified the distribution of cardiac output and the patterns of venous returns in the fetus. This pattern of circulatory response differs from that observed with other causes of reduced O2 delivery.
Article
Circulatory responses to hypoxemia and acidemia were studied in 10 fetal lambs, in utero with gestational ages of 122 to 142 days. Vinyl catheters were placed in fetal and maternal vessels, and the fetuses were studied 2 to 5 days postoperatively. Fetal heart rate, arterial pressure, P(O2), P(CO2), and pH were measured during a control period, and while the standing ewe breathed 6% oxygen and 3% carbon dioxide, through a plastic bag over its head. Fetal cardiac output and distribution and absolute organ blood flows were calculated from injections of 15μ nuclide labeled microspheres, during the control and hypoxemic states. One group of 5 fetuses only became hypoxemic (mean P(O2) 12, and mean pH 7.36), but the other 5 fetuses also developed acidemia (mean P(O2) 12, and mean pH 7.28). Fetal arterial P(CO2) values were normal throughout. During hypoxemia fetal arterial pressure increased, and fetal heart rate decreased. Although cardiac output fell in all but one fetus, the decrease was significant only in the acidemic group. Blood flow to the fetal body decrease in all, but the change was significantly greater in the acidemic group. Umbilical blood flow was maintained in all fetuses during hypoxemia. The percentage distribution of cardiac output to the placenta rose from 41 to 48% and from 41 to 57% in the hypoxemic and acidemic groups, respectively. Blood flow to the brain, heart, and adrenals increased 2 to 3 fold in all fetuses during hypoxemia while pulmonary, renal, splenic, gut, and carcass flows decreased. The changes were of greater magnitude in fetuses with combined hypoxemia and acidemia. These studies quantitate the fetal circulatory changes that occur in unanesthetized fetal lambs in utero during maternal hypoxemia.
Article
Techniques are described for insertion of vinyl catheters into the umbilical and limb vessels of the fetus of the sheep or the goat through small uterine incisions, with the ewes under spinal analgesia. The catheters are exteriorized and the fetus can be studied in its normal intrauterine environment. During constant infusion of antipyrine into a fetal limb vein, placental arteriovenous difference of antipyrine was measured, and fetal umbilical blood flow was calculated by the Fick method. "Carbonized" microspheres (50-µ diameter) labeled with various nuclides were injected into different venous sites in the fetus. The distribution pattern of the microspheres was used to determine the relative distribution of blood flow. Experimental evidence is provided that (1) there is no significant recirculation of microspheres, (2) the distribution of spheres is proportional to flow, and (3) circulatory physiology is not altered by injection of spheres. Quantitative data on the distribution of umbilical venous and superior and inferior vena caval return were obtained. It was possible to determine the actual blood flow to each of the fetal organs by relating the proportions of nuclide in each organ to that in the placenta. Total cardiac output was then calculable, taking into consideration the hemodynamic arrangement of the fetal circulation.
Article
The response of the uteroplacental and fetal circulations and oxygen transfer to injection of E. coli endotoxin into the pregnant sheep was investigated. Endotoxin injection into the mother was comprised of three distinct phases: First came a precipitous fall in arterial pressure and uteroplacental blood flow with an increase in uteroplacental vascular resistance. This phase was followed by a progressive recovery period during which flow, pressure, and resistance returned to control values. A third phase occurred during which arterial pressure and uteroplacental blood flow decreased until death of the animal. Despite the marked changes in uteroplacental hemodynamics and a decrease in uteroplacental oxygen transfer, the fetal circulation did not show any major alteration until the terminal phase of shock, when arterial pressure and umbilical flow decreased. There was a fall in fetal oxygen content difference.
Article
The effects of E. coli endotoxin upon fetal, immediate neonatal, and newborn (10 to 20 days) lamb circulation were studied. The fetus and immediate neonate tolerated doses 10 times greater than those proving lethal in adult pregnant sheep without exhibiting obvious signs of circulatory shock; arterial pressure, cardiac output, and vascular resistance were not significantly altered by these large doses. After 10 to 20 days of extrauterine life, the newborn lamb responded in a manner quite similar to the pregnant ewe; a biphasic acute response occurred after endotoxin injection followed by a slow decline in pressure and cardiac output until the termination of the experiment. We believe that the smaller response of the fetus and early neonate to endotoxin may be related not only to the presence of vascular shunts but also to a poorly developed adrenergic system.
Article
In order to determine the relative roles of O2 tension and content, CO2 tension, hydrogen ion concentration, arterial blood pressure, and cardiac output in the regulation of fetal cerebral blood flow (CBF), we used radioactively labeled microspheres to measure flow to 20 major brain regions in 24 chronically catheterized fetal lambs. We continually monitored fetal heart rate and blood pressure, and periodically measured arterial PO2, PCO2, pH, and hematocrit. In addition to CBF measurements during control periods, we measured CBF during: 1) hypoxia (O2 content less than 6 ml X dl-1; O2 tension less than 15 torr) induced by having the ewe breathe a gas mixture with low O2 concentration, 2) hypercapnia (PCO2 greater than 50 torr) induced by increasing the maternal inspired CO2, 3) acidosis and alkalosis (7.60 greater than pH greater than 6.60) induced by infusing lactic acid or bicarbonate into the fetus, and 4) hypotension (blood pressure less than 35 mm Hg) and hypertension (blood pressure greater than 55 mm Hg) induced by rapidly phlebotomizing or transfusing the fetus. We used multiple regression analysis and analysis of covariance to examine the dependence of total cerebral blood flow on arterial O2 tension and content, CO2 tension, pH, blood pressure, and cardiac output.(ABSTRACT TRUNCATED AT 250 WORDS)
Article
Incidence and time of onset of germinal matrix/intraventricular hemorrhage (GM/IVH) were prospectively ascertained in 1,105 infants weighing < or = 2,000 g at birth, a cohort comprising about 85% of all births of that weight born from September 1984 to June 1987 in the central New Jersey counties of Ocean, Monmouth, and Middlesex. Cranial ultrasonography was performed as nearly as possible to age 4 hours, 24 hours, and 7 days. Each scan was reviewed by two independent readers and, if necessary, a third; consensus was achieved on scan of first diagnosis of GM/IVH in 965 of the 1,079 infants with assessable scans. The cumulative incidence of GM/IVH in the first week of life was 24.6% (265/1,079). In the 965 infants with consensus diagnoses, the first scan, at 4.9 +/- 2.2 hours, yielded the highest incidence--10.6% (95/899). Incidence by the second scan (25.1 +/- 4.9 hours) was 6.0% (49/813), and by the third scan (7.2 +/- 0.8 days), 9.0% (64/715). The iterative algorithm for interval-censored data developed by Turnbull (J R Stat Soc [B] 1976;8:290-5) was used to estimate the most likely time of onset based on time of first diagnosis. From 34% to 44% of hemorrhages were present at the first opportunity to scan, which in these data was at age 1 hour. At least a third of GM/IVH in infants < or = 2,000 g appears to be of congenital or immediate postnatal onset.
Article
The interest in the study of endotoxemia in the clinical area has increased recently as a result of a) improved and simplified endotoxin determination e.g. chromogenic-kinetic microplate methods (also an improved blood sampling tool is available), b) incidence of sepsis has increased due to improvement in early (e.g. posttraumatic) survival, c) interest in and good evidence for gut translocation as a source of endotoxemia, d) agents have developed, which can antagonize endotoxins. There is evidence that patients with positive endotoxin test in the ICU have a higher incidence of organ failure. To study the pathophysiological consequences of endotoxemia and possible ways of intervention animal models are necessary. The choice of the experimental setting depends on the aim of the study e.g. whether prolonged observation is necessary in survival studies or whether hemodynamic variables have to be measured or whether therapeutic agents only crossreact with primates. Since LPS levels are quite low in clinical studies, an important factor for selection of a relevant animal might be LPS sensitivity, or the use of additional sensitization techniques e.g. galactosamine. Another important aspect in this context is whether LPS is given as bolus or infused up to several days. In this review the dose, time, and route of LPS administration is also discussed. For screening purposes rodents are usually used, or sometimes rabbits due to their higher LPS sensitivity. Another very sensitive animal model is the sheep, which can be chronically instrumented and as a specialty allows lung lymph drainage and thus studies of LPS effects on pulmonary permeability. Pigs are used for hemodynamic studies and often in therapeutical studies if species-specificity of the drug tested is not important, in cases where a large animal is necessary.
Article
Endothelin-1 produced by umbilicoplacental tissues may regulate fetal placental perfusion. To investigate its site of action, we measured segmental resistance in this bed in unanesthetized fetal sheep near term during fetal endothelin-1 infusion. A 15-min intravenous infusion of endothelin-1 at 1 micrograms/min significantly increased fetal blood pressure in the aorta (+33%), cotyledon artery and vein, and inferior vena cava, and endothelin-1 decreased fetal heart rate (-40%). Vascular resistance in the placental microcirculation increased significantly (+332%), but smaller increases in resistance of the umbilical artery and vein were not significant. Nevertheless, the stiffness of the umbilical arterial wall appeared to increase because vascular input impedance increased significantly both at the heart rate frequency (+85%) and when averaged > 2 Hz (characteristic impedance; +138%). Mean blood flow in the umbilical artery decreased by 64%, and the flow pulsatility index increased 137% (P < 0.05 for both). Despite the large decrease in placental perfusion, there was no significant change in descending aortic oxygen tension or oxygen content, because fetal oxygen consumption was reduced by 40%. We conclude that endothelin-1 is a potent constrictor of the placental microcirculation in sheep. Endothelin-1 also decreases fetal oxygen consumption by an unknown mechanism.
Article
To evaluate the hypothesis that the proinflammatory cytokines IL-1, IL-6, and tumor necrosis factor-alpha might be the link between prenatal intrauterine infection (IUI) and neonatal brain damage, the authors review the relevant epidemiologic and cytokine literature. Maternal IUI appears to increase the risk of preterm delivery, which in turn is associated with an increased risk of intraventricular hemorrhage, neonatal white matter damage, and subsequent cerebral palsy. IL-1, IL-6, and TNF-alpha have been found associated with IUI, preterm birth, neonatal infections. and neonatal brain damage. Unifying models not only postulate the presence of cytokines in the three relevant maternal/fetal compartments (uterus, fetal circulation, and fetal brain) and the ability of the cytokines to cross boundaries (placenta and blood-brain barrier) between these compartments, but also postulate how proinflammatory cytokines might lead to IVH and neonatal white matter damage during prenatal maternal infection. Interrupting the proinflammatory cytokine cascade might prevent later disability in those born near the end of the second trimester.
Article
Perinatal brain damage in the mature fetus is usually brought about by severe intrauterine asphyxia following an acute reduction of the uterine or umbilical circulation. The areas most heavily affected are the parasagittal region of the cerebral cortex and the basal ganglia. The fetus reacts to a severe lack of oxygen with activation of the sympathetic-adrenergic nervous system and a redistribution of cardiac output in favour of the central organs (brain, heart and adrenals). If the asphyxic insult persists, the fetus is unable to maintain circulatory centralisation, and the cardiac output and extent of cerebral perfusion fall. Owing to the acute reduction in oxygen supply, oxidative phosphorylation in the brain comes to a standstill. The Na(+)/K(+) pump at the cell membrane has no more energy to maintain the ionic gradients. In the absence of a membrane potential, large amounts of calcium ions flow through the voltage-dependent ion channel, down an extreme extra-/intracellular concentration gradient, into the cell. Current research suggests that the excessive increase in levels of intracellular calcium, so-called calcium overload, leads to cell damage through the activation of proteases, lipases and endonucleases. During ischemia, besides the influx of calcium ions into the cells via voltage-dependent calcium channels, more calcium enters the cells through glutamate-regulated ion channels. Glutamate, an excitatory neurotransmitter, is released from presynaptic vesicles during ischemia following anoxic cell depolarisation. The acute lack of cellular energy arising during ischemia induces almost complete inhibition of cerebral protein biosynthesis. Once the ischemic period is over, protein biosynthesis returns to pre-ischemic levels in non-vulnerable regions of the brain, while in more vulnerable areas it remains inhibited. The inhibition of protein synthesis, therefore, appears to be an early indicator of subsequent neuronal cell death. A second wave of neuronal cell damage occurs during the reperfusion phase. This cell damage is thought to be caused by the post-ischemic release of oxygen radicals, synthesis of nitric oxide (NO), inflammatory reactions and an imbalance between the excitatory and inhibitory neurotransmitter systems. Part of the secondary neuronal cell damage may be caused by induction of a kind of cellular suicide programme known as apoptosis. Knowledge of these pathophysiological mechanisms has enabled scientists to develop new therapeutic strategies with successful results in animal experiments. The potential of such therapies is discussed here, particularly the promising effects of i.v. administration of magnesium or post-ischemic induction of cerebral hypothermia.