[show abstract][hide abstract] ABSTRACT: The prevalence of births worldwide complicated by diabetes mellitus is increasing. In the UK, for example, <25% of diabetic women have a non-instrumental vaginal delivery. Strikingly, more than half the Caesarean sections (CS) in these patients are non-elective, but the reasons for this are not understood. We have tested the hypothesis that poor myometrial contractility as a consequence of the disease contributes to this high CS rate.
We compared spontaneous, high K depolarisation and oxytocin-induced contractions from diabetic and matched control patients having an elective CS. To investigate the mechanism of any differences we measured intracellular Ca, and performed western blotting and compared the tissues histologically.
There was significantly decreased contraction amplitude and duration in uteri from diabetic compared with control patients, even when possible confounders such as BMI were analysed. Reduced intracellular calcium signals and expression of calcium entry channels were found in uteruses from diabetic patients, which, along with a reduction in muscle content found on histological examination, could explain the reduced force. Myometrium from diabetic patients was responsive to oxytocin, but still did not reach the levels found in non-diabetic patients.
These are the first data investigating myometrium in diabetic patients and they support the hypothesis that there is poorer contractility even in the presence of oxytocin. The underlying mechanism is related to reduced Ca channel expression and intracellular calcium signals and a decrease in muscle mass. We conclude that these factors significantly contribute to the increased emergency CS rate in diabetic patients.
[show abstract][hide abstract] ABSTRACT: To assess the extent to which in vitro measurements of myometrial contractility reflect the clinical indication for caesarean section.
A prospective, observational hypothesis-generating study.
Women were recruited from Liverpool Women's NHS Foundation Trust and experiments were performed in the Physiology Department at the University of Liverpool.
Myometrial samples were taken from women undergoing a caesarean section during labour (n = 50) or from women having a repeat nonlabouring caesarean section (n = 70).
The demographic characteristics of the women and indications for current and previous caesarean sections were recorded. The force, frequency and duration of spontaneous contractions of myometrial strips, and changes in the intracellular calcium concentration of the strips, were measured. Kruskall-Wallis and post hoc tests were used to assess the significance of differences between groups.
Samples from women whose caesarean section was for fetal distress/acidosis (scalp pH <7.2) contracted with more force than those from women whose caesarean section was for delay in the first stage of labour (P < 0.001). For repeat, nonlabouring caesarean sections, samples from women whose first caesarean section was for fetal distress/acidosis also contracted with more force than did samples from women whose first caesarean section was for delay in the first stage of labour (P = 0.03).
These findings suggest that the myometrium contracts with greater force in women who have a caesarean section for fetal distress.
BJOG An International Journal of Obstetrics & Gynaecology 07/2011; 118(12):1499-506. · 3.76 Impact Factor
[show abstract][hide abstract] ABSTRACT: Worldwide, a significant number of diabetic pregnancies result in caesarean sections. We have investigated differences in the effects of insulin on myometrial contractility, and alterations in the expression of IRSβ in the myometrium between diabetic and non-diabetics.Methods
The effects of insulin (7 pM–700 nM) on myometrial contractility from consented term diabetic and non-diabetic women were examined. In some experiments intracellular Ca signals were simultaneously measured. Immunohistochemistry was used to examine the expression of IRSβ and quantified by colour based thresholding analysis.ResultsInsulin causes a dose dependent decrease in myometrial contractility in myometrium from both diabetic and non-diabetic women, which was mirrored in the underlying calcium transients. In non-diabetics the decrease was significant (p≤0.05) for all at concentrations, where as in diabetics the decrease was only significant at higher concentrations. At the highest concentrations of insulin the decrease in force in non-diabetics was significantly greater than the diabetics (22±11% n=15, 42±10% n=10, respectively) relative to control period. The results of the immunohistochemistry showed a significant reduction in amounts of IRSβ expressed in the myometrium of diabetics compared to non-diabetics (14±2% (n=8), 21±2% (n=8) respectively).Conclusions
The inhibitory effect of insulin on myometrial contractility was reduced in diabetics compared to non-diabetics, which may be due to alterations in expression of IRSβ in the myometrium. The reduction in calcium transients suggests insulin may affect calcium signalling pathways of the myometrium.
Archives of Disease in Childhood-fetal and Neonatal Edition - ARCH DIS CHILD-FETAL NEONATAL. 01/2011; 96(1).
[show abstract][hide abstract] ABSTRACT: To investigate the effect of maternal obesity on mode of delivery following induction of labour (IOL) for prolonged pregnancy and subsequent intrapartum and neonatal complications.
Retrospective (historical) cohort study.
Liverpool Women's Hospital NHS Foundation Trust, UK.
A total of 29, 224 women with singleton pregnancies between 2004 and 2008 of whom 3076 had a prolonged pregnancy (defined as ≥290 days or 41(+3) weeks of gestation) and received IOL.
Kruskal-Wallis test, chi-square test and multivariable logistic regression.
Mode of delivery and risk of delivery and neonatal complications in obese verses non-obese women following IOL.
Obese women had a significantly higher rate of IOL ending in caesarean section compared with women of normal weight following IOL (38.7% versus 23.8% primiparous; 9.9% versus 7.9% multiparous women, respectively); however, length of labour, incidence of postpartum haemorrhage and third-degree tear, rate of low cord blood pH, low Apgar scores and shoulder dystocia were similar in all body mass index categories. Complications included a higher incidence of fetal macrosomia and second-degree, but not third-degree, tear in primiparous women.
Higher maternal body mass index at booking is associated with an increased risk of prolonged pregnancy and increased rate of IOL. Despite this, more than 60% of obese primiparous and 90% of multiparous women with prolonged pregnancies who were induced achieved vaginal delivery and labour complications in the obese women with prolonged pregnancies were largely comparable to those of normal weight women with prolonged pregnancies. Our data suggest that IOL for prolonged pregnancy in obese women is a reasonable and safe management option.
BJOG An International Journal of Obstetrics & Gynaecology 01/2011; 118(5):578-88. · 3.76 Impact Factor
[show abstract][hide abstract] ABSTRACT: The higher levels of stretch present in the uterus of multiple pregnancy mothers is implicated in the higher rates of preterm labour they exhibit. The relaxant effect of progesterone in multiple pregnancies is reduced in comparison to singletons by unknown mechanisms. Our aims were therefore to compare in vitro the response of myometrium from singletons and twin pregnancies to progesterone and examine the effects of stretch on the response to progesterone (10 µM).Methods
Informed consent term biopsies were taken and contractility measured. After control measurements, in some tissues stretch was applied to 100% of the maximal response to 40 mM K+. Time and vehicle (EtOH) controls were also performed.ResultsProgesterone exposure produced a reduction in force amplitude significantly greater in singleton (16) tissue than twins (10) at 10 and 100 µM. Twin data (n=5) also indicates that the effects of 10 µM progesterone were attenuated in response to mechanical stretch compared to non-stretched controls – an effect that preliminary data suggests is more pronounced in twins than singletons.Conclusions
These data show significant differences in multiple pregnancies in myometrial response to progesterone and suggest that stretch can reduce the tocolytic ability of progesterone. The reduced efficacy of progesterone in twins, may be due to accelerated switching in progesterone isoforms in preparation for labour in multiple pregnancies, and is consistent with clinical findings, but leaves open the question of whether higher progesterone doses would be efficacious.
Archives of Disease in Childhood-fetal and Neonatal Edition - ARCH DIS CHILD-FETAL NEONATAL. 01/2011; 96(1).
[show abstract][hide abstract] ABSTRACT: Twins in utero and their mothers are at a variety of risks; for example pre-eclampsia and prematurity. Large scale studies and reviews have confirmed a tocolytic benefit of progesterone in singleton pregnancies. In multiples however, similar studies have shown no benefit of progesterone. The reason for this difference is unknown. The authors considered it important therefore to investigate, under controlled in vitro conditions, how myometrium from singleton and multiple pregnancies responds to different doses of progesterone.Methods
Myometrial strips were prepared from biopsies obtained with informed consent from seven women with multiple pregnancy and six singletons undergoing Caesarean section at term. Strips were attached to a force transducer, superfused with physiological saline, and once stable contractions arose, cumulative doses of hydroxyl-progesterone from 1 to 100 μM were applied.ResultsContraction frequency was greater in the multiple pregnancies than singletons, but their amplitudes were comparable. A striking difference between multiples and singletons was found in the progesterone dose-response curves, with significant resistance to progesterone's effects being found in the former; at 10 μM progesterone, compared to control amplitude (100%), multiples produced significantly more force than singletons (62%±4% and 30%±14%, respectively, p=0.0048).Conclusion
These preliminary results suggest significant differences in both the inherent contractile properties in multiple pregnancies and in myometrial response to progesterone. The reduced efficacy of progesterone may be due to accelerated switching in progesterone isoforms in preparation for labour in multiple pregnancies, and is consistent with clinical findings, but leaves open the question of whether higher progesterone doses would be efficacious.
Archives of Disease in Childhood-fetal and Neonatal Edition - ARCH DIS CHILD-FETAL NEONATAL. 01/2010; 95(1).
[show abstract][hide abstract] ABSTRACT: Diabetes in pregnancy accounts for a disproportionately high rate of Caesarean sections (CS). Insulin is widely prescribed to attain normoglycaemia in diabetic pregnancies. The authors analysed the effect of insulin on spontaneous and oxytocin-induced myometrial contractility.Methods
Contractility and simultaneous intracellular Ca signals in response to increasing concentrations of insulin (7 pM to 700 nM) were recorded from both human and late pregnant rat myometrial strips. These were dissected from biopsies obtained with full consent from women undergoing term elective CS and rats humanely killed at late gestation (22 days). Ouabain (Na pump inhibitor) or tetraethylammonium (K channel inhibitor) was added to contracting myometrium combined with insulin to examine the mechanism of insulins action.ResultsA dose dependent decrease in contractility in response to insulin was observed in human (n=11) and rat myometrium (n=5) which was significant at concentrations ≥7 nM relative to control period. The decrease in force was mirrored in the underlying Ca transients. Insulin caused a significant greater decrease in myometrial contractility in non-diabetics (n=11) compared to diabetics (n=8). Both 10 μM ouabain and 5 mM tetraethylammonium (TEA) with insulin inhibited the negative effect of insulin on contractility.Conclusion
Insulin causes a dose-dependent decrease in amplitude of spontaneous and oxytocin stimulated contractions in human and rat myometrium. The decrease in calcium transients suggests that insulin is acting by decreasing calcium currents, and may partially stimulate the Na pump resulting in cell hyperpolarisation The inhibitory effect of TEA on myometrial responses to insulin suggests insulin may also impede conductance of K+.
Archives of Disease in Childhood-fetal and Neonatal Edition - ARCH DIS CHILD-FETAL NEONATAL. 01/2010; 95(1).
[show abstract][hide abstract] ABSTRACT: The aim of the study was to elucidate the reason for the high rate of caesarean section in obese women. We examined the following hypotheses: (1) obese women have a high incidence of complications related to poor uterine contractility--caesarean section for dysfunctional labour and postpartum haemorrhage. 2) The myometrium from obese women has less ability to contract in vitro.
First, a clinical retrospective analysis of data from 3913 completed singleton pregnancies was performed. Secondly, in a prospective study the force, frequency and intracellular [Ca(2+)] flux of spontaneously contracting myometrium were related to the maternal body mass index.
Liverpool Women's Hospital and University of Liverpool.
The clinical study involved all women who delivered in one hospital in 2002. The in vitro study myometrial biopsies were obtained from 73 women who had elective caesarean section at term.
Maternal obesity carried significant risk of caesarean section in labour that was highest for delay in the first stage of labour (OR 3.54). The increased risk of caesarean section in obese women largely occurred in women with normal- and not with high-birthweight infants. Obese women delivering vaginally had increased risk of prolonged first stage of labour and excessive blood loss. Myometrium from obese women contracted with less force and frequency and had less [Ca(2+)] flux than that from normal-weight women.
We suggest that these findings indicate that obesity may impair the ability of the uterus to contract in labour.
BJOG An International Journal of Obstetrics & Gynaecology 04/2007; 114(3):343-8. · 3.76 Impact Factor
[show abstract][hide abstract] ABSTRACT: To characterize the contractile responses of mouse myometrium, the associated calcium (Ca2+) changes and the role of the sarcoplasmic reticulum (SR), and to better understand excitation contraction coupling in this tissue.
Strips of longitudinal myometrium were used, and Ca2+ was measured after loading with Indo-1.
Intracellular Ca2+ transients, produced by Ca2+ entry, preceded phasic spontaneous contractions. Depolarization with high potassium concentration significantly increased the amplitude of the contractions and transformed the pattern of activity from phasic to tonic, with accompanying changes in intracellular Ca2+ concentration ([Ca2+]i). Oxytocin significantly stimulated contractile activity and [Ca2+]i above the level occurring spontaneously. Thus all forms of contractile activity were closely correlated with Ca2+. When the SR was emptied using a blocker of the SR calcium-adenosinetriphosphatase, cyclopiazonic acid, spontaneous Ca2+ and force transients increased greatly in frequency and amplitude. Ryanodine, a blocker of Ca(2+)-induced Ca2+ release (CICR), did not impair activity. In the absence of external Ca2+, oxytocin was able to release Ca2+ from the SR through IP3 but produced only a small increase in force, demonstrating a requirement for Ca2+ entry as part of the mechanism of agonist action.
Mouse myometrium, (1) produces contractile activity reflecting changes in [Ca2+]i irrespective of the stimulus, (2) has a significant SR Ca2+ content releasable by agonists but not CICR, (3) has an SR acting to inhibit spontaneous activity, and (4) behaves qualitatively similarly to human and rat myometrium in major aspects of excitation contraction coupling and is therefore a useful model tissue.
Journal of the Society for Gynecologic Investigation 06/2004; 11(4):207-12. · 2.26 Impact Factor
[show abstract][hide abstract] ABSTRACT: The regulation of contractile activity in smooth muscle cells involves rapid discrimination and processing of a multitude of simultaneous signals impinging on the membrane before an integrated functional response can be generated. The sarcolemma of smooth muscle cells is segregated into caveolar regions-largely identical with cholesterol-rich membrane rafts-and actin-attachment sites, localized in non-raft, glycerophospholipid regions. Here we demonstrate that selective extraction of cholesterol abolishes membrane segregation and disassembles caveolae. Simultaneous measurements of force and [Ca2+]i in rat ureters demonstrated that extraction of cholesterol resulted in inhibition of both force and intracellular Ca2+ signals. Considering the major structural reorganization of cholesterol-depleted sarcolemma, it is intriguing to note that decreased levels of membrane cholesterol are accompanied by a highly specific inhibition of phasic, but not tonic contractions. This implies that signalling cascades that ultimately lead to either phasic or tonic response may be spatially segregated in the plane of the sarcolemma. Replenishment of cholesterol restores normal contractile behavior. In addition, the tissue function is re-established by inhibiting the large-conductance K(+)-channel. Sucrose gradient ultracentrifugation in combination with Western blotting analysis demonstrates that its alpha-subunit is associated with detergent-resistant membranes, suggesting that the channel might be localized within the membrane rafts in vivo. These findings are important in understanding the complex signalling pathways in smooth muscle and conditions such as premature labor and hypertension.
Journal of Membrane Biology 04/2004; 198(2):95-101. · 2.48 Impact Factor
[show abstract][hide abstract] ABSTRACT: Obstructed labour is an important cause of maternal deaths in communities in which undernutrition in childhood is common resulting in small pelves in women, and in which there is no easy access to functioning health facilities with the capability of carrying out operative deliveries. Obstructed labour also causes significant maternal morbidity in the short term (notably infection) and long term (notably obstetric fistulas). Fetal death from asphyxia is also common. There are differences in the behaviour of the uterus during obstructed labour, depending on whether the woman has delivered previously. The pattern in primigravid women (typically diminishing contractility with risk of infection and fistula) may result from tissue acidosis, whereas in parous women, contractility may be maintained with the risk of uterine rupture. Ultimately, tackling the problem of obstructed labour will require universal adequate nutritional intake from childhood and the ability to access adequately equipped and staffed clinical facilities when problems arise in labour. These seem still rather distant aspirations. In the meantime, strategies should be implemented to encourage early recognition of prolonged labour and appropriate clinical responses. The sequelae of obstructed labour can be an enormous source of human misery and the prevention of obstetric fistulas, and skilled treatment if they do occur, are important priorities in regions where obstructed labour is still common.
British Medical Bulletin 02/2003; 67:191-204. · 4.36 Impact Factor
[show abstract][hide abstract] ABSTRACT: 1. To assess the contribution of the sarcoplasmic reticulum calcium store in the generation of uterine smooth muscle contractions; 2. to evaluate the contribution of calcium induced calcium release or ryanodine gated calcium channels to myometrial force production.
Laboratory scientific study.
Myometrial strips were obtained from women undergoing elective prelabour caesarean section at term. These were loaded with the calcium sensitive indicator Indo-1 allowing simultaneous assessment of intracellular calcium concentrations and force production. The effect of exposing the strips to ryanodine (which abolishes calcium induced calcium release), caffeine (which activates calcium induced calcium release) and cyclopiazonic acid (which abolishes the sarcoplasmic reticulum calcium store) was examined.
Exposure to ryanodine had no appreciable effect on either the amplitude or the duration of the myometrial calcium and force transients but did increase the frequency of contractions (139+/-5%). Caffeine did not potentiate force. Cyclopiazonic acid increased frequency, duration and amplitude of both calcium and force transients. The ability of oxytocin to provoke calcium and force transients in the absence of extracellular calcium was abolished by cyclopiazonic acid but not by ryanodine.
These results demonstrate that calcium induced calcium release does not play a significant role in human myometrium and that no functioning role for the ryanodine receptors in human myometrial tissue could be shown. These data suggest that the sarcoplasmic reticulum may act to limit contractions and act as a calcium sink, rather than to amplify contractions.
BJOG An International Journal of Obstetrics & Gynaecology 04/2002; 109(3):289-96. · 3.76 Impact Factor
[show abstract][hide abstract] ABSTRACT: Recent work has indicated that smooth muscle force production may be influenced by pathways not dependent upon the Ca2+-calmodulin phosphorylation of light chains. Few studies, however, have examined the importance of these pathways in intact muscles that contract phasically rather than tonically. Therefore, to determine whether the Ca2+-independent Rho-A and associated kinase (ROK) pathway can affect contractions of the intact human myometrium, we used Y-27632 to inhibit ROK. Three types of contractile activity were examined: spontaneous and those elicited by oxytocin and by depolarisation by high K+. Y-27632 decreased force significantly under all three conditions, without changing intracellular [Ca2+]. However, the effects on force were only large when the uterus was producing force tonically rather than phasically. This suggests that the Rho-A-ROK pathway may not be a potent modulator of force in the human myometrium under physiological conditions.
Pflügers Archiv - European Journal of Physiology 11/2001; 443(1):112-4. · 4.87 Impact Factor
[show abstract][hide abstract] ABSTRACT: Intracellular pH can have profound effects on tissue function, but little is known about how pH is regulated, buffered or affects the function of gastric smooth muscle. As the pH of gastric myocytes may alter with pathophysiological disturbance of the gastric lining, or reduction in blood flow to the stomach, these parameters were investigated. Intracellular pH was measured in strips of corpus from rats and guinea-pigs and pH perturbed by the addition of Na butyrate. pH regulation was investigated using pharmacological inhibitors and ionic substitutions. Resting pH was found to be around 7.0, and buffering power relatively high, compared to other muscles in both species. In the guinea-pig amiloride, EIPA and HOE694 prevented pH regulation from an acid load, but amiloride- and EIPA-insensitive pH-regulating mechanisms were found in the rat. The pH-regulatory mechanism present in the rat was also insensitive to DIDS, SITS and removal of external Cl-, but inhibited by Na+ substitution and HOE694. Acidification reduced gastric tone in both species. We conclude that pH alteration will significantly affect gastric contractility, despite a high capacity of the tissue to buffer and regulate pH change. The sensitivity to NHE inhibitors differs between rat and guinea-pig, suggesting that Na+/H+ exchanger isoform expression differs between gastric tissue.
Pflügers Archiv - European Journal of Physiology 07/2001; 442(3):459-66. · 4.87 Impact Factor