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ABSTRACT: AIM: The renal medulla plays an important role in the control of water and salt balance by the kidney. Outer medullary descending vasa recta (OMDVR) are microscopic vessels providing blood flow to the renal medulla. Data on the physiology of human vasa recta are scarce. Therefore we established an experimental model of human single isolated perfused OMDVR, and characterized their vasoactivity in response to angiotensin II and to pressure changes. Methods: Human non-malignant renal tissue was obtained from patients undergoing nephrectomy due to renal cell carcinoma. OMDVR were dissected under magnification and perfused using concentric microscopic pipettes. The response of OMDVR to angiotensin II and pressure changes was quantified in serial pictures. All patients signed a consent form prior to surgery. Results: OMDVR constricted significantly after bolus applications of angiotensin II. OMDVR constriction to angiotensin II was also concentration dependent. Response to luminal pressure changes were different according to the diameter of vessels, with larger OMDVR constricting after pressure increase, while smaller ones did not. Conclusion: OMDVR constrict in response to angiotensin II and pressure increases. Our results show that OMDVR may take part in the regulation of medullary blood flow in humans. Our model may be suitable for investigating disturbances of renal medullary circulation in human subjects. Acta Physiologica © 2013 Scandinavian Physiological Society.
Acta Physiologica 02/2013; · 3.09 Impact Factor
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ABSTRACT: Few territories of the our bodies are as remarkable and simultaneously as small as the renal medulla. Its "U"-shaped arrangement of vessels and tubules, the counter-current mechanism, the peculiar, selective ion transport and permeability of different segments to water and ions, and the resulting high osmolar milieu, are indeed unique - actually, it is the length of this "U"-shaped loops that seems to ultimately determine the ability of the kidneys to concentrate urine (Schmidt-Nielsen & Schmidt-Nielsen 2011). No wonder that, since the classic works of Gottschalk and collaborators in the 50's (Gottschalk & Mylle 1959), it is most commonly in the context of urine concentration that the renal medulla is thought about. Acta Physiologica © 2013 Scandinavian Physiological Society.
Acta Physiologica 02/2013; · 3.09 Impact Factor
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ABSTRACT: Contrast induced acute kidney injury (CIAKI) is an important clinical event with a worldwide increasing number of cases. Medullary hypoperfusion and hypoxia due to constriction of vasa recta are main factors in the pathophysiology of AKI. However, the mechanism of contrast media (CM) induced vessel constriction is not known. We tested the hypothesis that vasa recta constriction is a consequence of endothelial dysfunction due to the cytotoxicity of CM. Human and rat DVR were isolated, perfused with CM, and the luminal diameter analyzed. For morphological analysis of the endothelium, renal arteries were CM perfused and then processed for electron microscopy. Transcellular electrical resistance was used to estimate CM-induced changes in the permeability of HUVEC cell layers. Perfusion with CM constricted human and rat DRV (to 54.3% and 50.9% of initial diameter, respectively). This was blunted by adrenomedullin (77.7% and 77.1%, respectively). The angiotensin II response was enhanced by CM in rat DVR (reduction to 15.6% and 35.0% of initial diameter, respectively). Adrenomedullin blunted this effect (67.5%). CM led to endothelial damage of renal arteries characterized by a ragged surface, with sharply protruding intimal folds, spindle-like shape, and bulging into the lumen. These phenomena were reduced by adrenomedullin. The permeability of HUVEC cell layers was increased by CM and this went along with increased myosin light chain phosporylation. Again, adremonedullin reduced the CM effect. The study suggests that the constrictor effect of CM on the renal medullary microvasculature is a consequence of endothelial cell damage and the resulting endothelial dysfunction.
AJP Renal Physiology 10/2012; · 4.42 Impact Factor
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ABSTRACT: Purpose:To determine the effect of the iodinated contrast medium iodixanol on arteriolar tone in afferent and efferent arterioles of the glomerulus and the functional interactions with the major modulators of arteriolar tone, angiotensin II and nitric oxide, in mice.Materials and Methods:Animal handling conformed to the ethics guidelines of the Office for Health and Social Matters of Berlin. Arterioles were isolated from 136 C57BL/6 mice, perfused with either vehicle solution or iodixanol (23 mg of iodine per milliliter) for 20 minutes, followed by angiotensin II administration. Fluorescence of 3-amino-4-(N-methylamino)-2',7'-difluorofluorescein (DAF-FM) and dihydroethidium (DHE) were used for quantification of nitric oxide bioavailability and superoxide concentration, respectively. Statistical analysis of time- and dose-dependent data was performed by using the nonparametric test for repeated measurements.Results:With iodixanol, afferent arteriole diameters were significantly reduced from 9.2 µm to 8.3 µm; in control group, the diameters were increased from 8.7 µm to 9.3 µm (P = .008). Nitric oxide synthase inhibition augmented iodixanol-induced constriction, with diameters reduced from 9.9 µm to 5.8 µm (P < .0001). DAF-FM fluorescence increased less during iodixanol treatment and nitric oxide synthase inhibition (3.6% and 3.7% vs 10.7% in control group, P = .009 and P = .049, respectively), indicating impaired nitric oxide bioavailability. With iodixanol, DHE fluorescence ratio was increased by 12% (P < .0001). Angiotensin II responses were enhanced by iodixanol and by nitric oxide synthase inhibition after perfusion with iodixanol (3.3 µm and 4.3 µm vs 7.5 µm [control group] with 1 × 10(-6)/mol/L angiotensin II, P = .03 for both). In contrast, in efferent arterioles, neither their basal diameters nor the responses to angiotensin II were significantly affected by iodixanol.Conclusion:A more pronounced effect of iodixanol on afferent than on efferent arterioles may contribute to the reduction of glomerular filtration rate in contrast medium-induced acute kidney injury. Decreased nitric oxide bioavailability and increased concentration of superoxide explain the increased tone and reactivity in afferent arterioles perfused with iodixanol.© RSNA, 2012Supplemental material: http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.12120044/-/DC1.
Radiology 09/2012; · 5.73 Impact Factor
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ABSTRACT: Functional sex differences are described in several vascular beds. In the case of renal vessels, sex differences could influence processes like regulation of blood pressure and ion balance. Angiotensin II and nitric oxide are important regulators of renal vascular tone. Females have higher nitric oxide synthase expression, nitric oxide bioavailability and ratio of angiotensin II type 2/type 1 receptors. Thus, our objective was to examine whether renal interlobar arteries present sex differences in their response to angiotensin II, and whether angiotensin II type 2 receptors play a role in such differences.
We investigated the isometric contraction and relaxation of interlobar arteries from female and male mice under blockade of nitric oxide synthases and angiotensin II type 2 receptors. We also investigated the expression of angiotensin II receptors (type 1 and 2) and endothelial nitric oxide synthase.
Significantly less intense contraction to angiotensin II were seen in arteries from females in comparison to male mice. Inhibition of nitric oxide synthases and endothelial removal abolished this difference. Angiotensin II type 2 receptors blockade enhanced contraction to angiotensin II in females, but not in males. Endothelial-dependent vasodilation was more dependent on nitric oxide in females than in males. Expression of angiotensin II type 1 and type 2 receptors was similar between sexes. Expression of endothelial nitric oxide synthase was higher in females.
A sex-specific, nitric oxide-mediated effect via angiotensin II type 2 receptors underlies the sex differences in the response of interlobar arteries to angiotensin II. Our findings may help understanding sex differences in renal hemodynamics and blood pressure control.
Journal of hypertension 09/2012; 30(9):1791-8. · 4.02 Impact Factor
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Michael Fähling,
Anja Bondke Persson,
Bertram Klinger,
Edgar Benko,
Andreas Steege,
Mumtaz Kasim, Andreas Patzak,
Pontus B Persson,
Gunter Wolf,
Nils Blüthgen,
Ralf Mrowka
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ABSTRACT: Hypoxia-inducible factor-1 (HIF-1) is a well-studied transcription factor mediating cellular adaptation to hypoxia. It also plays a crucial role under normoxic conditions, such as in inflammation, where its regulation is less well understood. The 3'-untranslated region (UTR) of HIF-1α mRNA is among the most conserved UTRs in the genome, hinting toward posttranscriptional regulation. To identify potential trans factors, we analyzed a large compilation of expression data. In contrast to its known function of being a negative regulator, we found that tristetraprolin (TTP) positively correlates with HIF-1 target genes. Mathematical modeling predicts that an additional level of posttranslational regulation of TTP can explain the observed positive correlation between TTP and HIF-1 signaling. Mechanistic studies revealed that TTP indeed changes its mode of regulation from destabilizing to stabilizing HIF-1α mRNA upon phosphorylation by p38 mitogen-activated protein kinase (MAPK)/MAPK-activated protein kinase 2. Using a model of monocyte-to-macrophage differentiation, we show that TTP-driven HIF-1α mRNA stabilization is crucial for cell migration. This demonstrates the physiological importance of a hitherto-unknown mechanism for multilevel regulation of HIF-1α in normoxia.
Molecular biology of the cell 08/2012; 23(20):4129-41. · 5.98 Impact Factor
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ABSTRACT: Adenosine mediates tubuloglomerular feedback responses via activation of A(1)-receptors on the renal afferent arteriole. Increased preglomerular reactivity, due to reduced nitric oxide (NO) production or increased levels of ANG II and reactive oxygen species (ROS), has been linked to hypertension. Using A(1)-receptor knockout (A(1)(-/-)) and wild-type (A(1)(+/+)) mice we investigated the hypothesis that A(1)-receptors modulate arteriolar and blood pressure responses during NO synthase (NOS) inhibition or ANG II treatment. Blood pressure and renal afferent arteriolar responses were measured in nontreated mice and in mice with prolonged N(ω)-nitro-L-arginine methyl ester hydrochloride (L-NAME) or ANG II treatment. The hypertensive responses to L-NAME and ANG II were clearly attenuated in A(1)(-/-) mice. Arteriolar contractions to L-NAME (10(-4) mol/l; 15 min) and cumulative ANG II application (10(-12) to 10(-6) mol/l) were lower in A(1)(-/-) mice. Simultaneous treatment with tempol (10(-4) mol/l; 15 min) attenuated arteriolar responses in A(1)(+/+) but not in A(1)(-/-) mice, suggesting differences in ROS formation. Chronic treatment with L-NAME or ANG II did not alter arteriolar responses in A(1)(-/-) mice, but enhanced maximal contractions in A(1)(+/+) mice. In addition, chronic treatments were associated with higher plasma levels of dimethylarginines (asymmetrical and symmetrical) and oxidative stress marker malondialdehyde in A(1)(+/+) mice, and gene expression analysis showed reduced upregulation of NOS-isoforms and greater upregulation of NADPH oxidases. In conclusion, adenosine A(1)-receptors enhance preglomerular responses during NO inhibition and ANG II treatment. Interruption of A(1)-receptor signaling blunts l-NAME and ANG II-induced hypertension and oxidative stress and is linked to reduced responsiveness of afferent arterioles.
AJP Regulatory Integrative and Comparative Physiology 12/2011; 301(6):R1669-81. · 3.34 Impact Factor
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ABSTRACT: To identify the muscarinic acetylcholine receptor subtype that mediates cholinergic vasodilation in murine retinal arterioles.
Muscarinic receptor gene expression was determined in murine retinal arterioles using real-time PCR. To assess the functional relevance of muscarinic receptors for mediating vascular responses, retinal vascular preparations from muscarinic receptor-deficient mice were studied in vitro. Changes in luminal arteriole diameter in response to muscarinic and nonmuscarinic vasoactive substances were measured by video microscopy.
Only mRNA for the M(3) receptor was detected in retinal arterioles. Thus, M(3) receptor-deficient mice (M3R(-/-)) and respective wild-type controls were used for functional studies. Acetylcholine concentration-dependently dilated retinal arterioles from wild-type mice. In contrast, vasodilation to acetylcholine was almost completely abolished in retinal arterioles from M3R(-/-) mice, whereas responses to the nitric oxide (NO) donor nitroprusside were retained. Carbachol, an acetylcholinesterase-resistant analog of acetylcholine, also evoked dilation in retinal arterioles from wild-type, but not from M3R(-/-), mice. Vasodilation responses from wild-type mice to acetylcholine were negligible after incubation with the non-subtype-selective muscarinic receptor blocker atropine or the NO synthase inhibitor N(ω)-nitro-L-arginine methyl ester, and were even reversed to contraction after endothelial damage with 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate.
These findings provide evidence that endothelial M(3) receptors mediate cholinergic vasodilation in murine retinal arterioles via activation of NO synthase.
Investigative ophthalmology & visual science 08/2011; 52(10):7479-84. · 3.43 Impact Factor
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ABSTRACT: To identify the α(1)-adrenoceptor (α(1)-AR) subtypes mediating vascular adrenergic responses in murine ophthalmic arteries.
Expression of mRNA was quantified for individual α(1)-AR subtypes in murine ophthalmic arteries using real-time PCR. To assess the functional relevance of α(1)-ARs for mediating vascular responses, ophthalmic arteries from mice deficient in one of the three α(1)-AR subtypes (α(1A)-AR(-/-), α(1B)-AR(-/-), and α(1D)-AR(-/-), respectively) and wild-type controls were isolated, cannulated with micropipettes, and pressurized. Changes in luminal artery diameter in response to the α(1)-AR agonist phenylephrine, the sympathetic transmitter noradrenaline, and to the nonadrenergic vasoconstrictor arginine vasopressin (AVP) were measured by video microscopy.
Using real-time PCR, mRNA for all three α(1)-AR subtypes was detected in ophthalmic arteries from wild-type mice. In functional studies, phenylephrine and noradrenaline produced dose-dependent constriction of ophthalmic arteries that was similar in wild-type, α(1B)-AR(-/-), and α(1D)-AR(-/-) mice. Strikingly, responses to phenylephrine and noradrenaline were almost completely abolished in α(1A)-AR(-/-) mice. In contrast, the nonadrenergic agonist AVP produced dose-dependent vasoconstrictor responses that did not differ between any of the mouse genotypes tested.
These findings provide evidence that the α(1A)-AR subtype mediates adrenergic vasoconstriction in murine ophthalmic arteries.
Investigative ophthalmology & visual science 05/2011; 52(7):4795-9. · 3.43 Impact Factor
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ABSTRACT: Pulse transit time (PTT) and pulse wave velocity (PWV), respectively, were shown to have a correlation with systolic blood pressure (SBP) and have been reported to be suitable for indirect BP measurements. The aim of this study was to create a function between SBP and PWV, and to test its reliability for the determination of absolute SBP using a non-linear algorithm and a one-point calibration. 63 volunteers performed exercise to induce rises in BP. Arterial PTT was measured between the R-spike of the ECG and the plethysmographic curve of finger pulse-oximetry. The reference BP was measured using a cuff-based sphygmomanometric aneroid device. Data from 13 of the 63 volunteers served for the detection of the PWV-BP relationship. The created non-linear function was used to calculate BP values after individual correction for the BP offset in a group of 50 volunteers. Individual correlation coefficients for SBP measured by PTT (SBP(PTT)) and by cuff (SBP(CUFF)) varied between r = 0.69 and r = 0.99. Taking all data together, we found r = 0.83 (276 measurements in 50 volunteers). In the Bland-Altman plot, the limits of agreement were [Formula: see text]± 19.8 mmHg. In conclusion, comparing SBP values using the PTT-based method and those measured by cuff resulted in a significant correlation. However, the Bland-Altman plot shows relevant differences between both methods, which are partly due to greater variability of the SBP(PTT) measurement during intensified exercise. Results suggest that PTT can be used for measuring absolute SBP when performing an individual correction for the offset of the BP-PWV relation.
Arbeitsphysiologie 05/2011; 112(1):309-15. · 2.15 Impact Factor
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Janice Schildroth,
Juliane Rettig-Zimmermann,
Philipp Kalk,
Andreas Steege,
Michael Fähling,
Mauricio Sendeski,
Alexander Paliege,
En Yin Lai,
Sebastian Bachmann,
Pontus B Persson,
Berthold Hocher, Andreas Patzak
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ABSTRACT: Endothelin 1 contributes to renal blood flow control and pathogenesis of kidney diseases. The differential effects, however, of endothelin 1 (ET-1) on afferent (AA) and efferent arterioles (EA) remain to be established.
We investigated endothelin type A and B receptor (ETA-R, ETB-R) functions in the control of AA and EA. Arterioles of ETB-R deficient, rescued mice [ETB(-/-)] and wild types [ETB(+/+)] were microperfused.
ET-1 constricted AA stronger than EA in ETB(-/-) and ETB(+/+) mice. Results in AA: ET-1 induced similar constrictions in ETB(-/-) and ETB(+/+) mice. BQ-123 (ETA-R antagonist) inhibited this response in both groups. ALA-ET-1 and IRL1620 (ETB-R agonists) had no effect on arteriolar diameter. L-NAME did neither affect basal diameters nor ET-1 responses. Results in EA: ET-1 constricted EA stronger in ETB(+/+) compared to ETB(-/-). BQ-123 inhibited the constriction completely only in ETB(-/-). ALA-ET-1 and IRL1620 constricted only arterioles of ETB(+/+) mice. L-NAME decreased basal diameter in ETB(+/+), but not in ETB(-/-) mice and increased the ET-1 response similarly in both groups. The L-NAME actions indicate a contribution of ETB-R in basal nitric oxide (NO) release in EA and suggest dilatory action of ETA-R in EA.
ETA-R mediates vasoconstriction in AA and contributes to vasoconstriction in EA in this mouse model. ETB-R has no effect in AA but mediates basal NO release and constriction in EA. The stronger effect of ET-1 on AA supports observations of decreased glomerular filtration rate to ET-1 and indicates a potential contribution of ET-1 to the pathogenesis of kidney diseases.
Nephrology Dialysis Transplantation 03/2011; 26(3):779-89. · 3.40 Impact Factor
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ABSTRACT: Acetylcholine regulates perfusion of numerous organs via changes in local blood flow involving muscarinic receptor-induced release of vasorelaxing agents from the endothelium. The purpose of the present study was to determine the role of M₁, M₃, and M₅ muscarinic acetylcholine receptors in vasodilation of small arteries using gene-targeted mice deficient in either of the three receptor subtypes (M1R(-/-), M3R(-/-), or M5R(-/-) mice, respectively). Muscarinic receptor gene expression was determined in murine cutaneous, skeletal muscle, and renal interlobar arteries using real-time PCR. Moreover, respective arteries from M1R(-/-), M3R(-/-), M5R(-/-), and wild-type mice were isolated, cannulated with micropipettes, and pressurized. Luminal diameter was measured using video microscopy. mRNA for all five muscarinic receptor subtypes was detected in all three vascular preparations from wild-type mice. However, M(3) receptor mRNA was found to be most abundant. Acetylcholine produced dose-dependent dilation in all three vascular preparations from M1R(-/-), M5R(-/-), and wild-type mice. In contrast, cholinergic dilation was virtually abolished in arteries from M3R(-/-) mice. Deletion of either M₁, M₃, or M₅ receptor genes did not affect responses to nonmuscarinic vasodilators, such as substance P and nitroprusside. These findings provide the first direct evidence that M₃ receptors mediate cholinergic vasodilation in cutaneous, skeletal muscle, and renal interlobar arteries. In contrast, neither M₁ nor M₅ receptors appear to be involved in cholinergic responses of the three vascular preparations tested.
AJP Heart and Circulatory Physiology 02/2011; 300(5):H1602-8. · 3.71 Impact Factor
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ABSTRACT: Descending vasa recta (DVR) are 12- to 15-μm microvessels that supply the renal medulla with blood flow. We examined the ability of intrinsic nitric oxide (NO) and reactive oxygen species (ROS) generation to regulate their vasoactivity. Nitric oxide synthase (NOS) inhibition with N(ω)-nitro-l-arginine methyl ester (l-NAME; 100 μmol/l), or asymmetric N(G),N(G)-dimethyl-l-arginine (ADMA; 100 μmol/l), constricted isolated microperfused DVR by 48.82 ± 4.34 and 27.91 ± 2.91%, respectively. Restoring NO with sodium nitroprusside (SNP; 1 mmol/l) or application of 8-Br-cGMP (100 μmol/l) reversed DVR vasoconstriction by l-NAME. The superoxide dismutase mimetic Tempol (1 mmol/l) and the NAD(P)H inhibitor apocynin (100, 1,000 μmol/l) also blunted ADMA- or l-NAME-induced vasoconstriction, implicating a role for concomitant generation of ROS. A role for ROS generation was also supported by an l-NAME-associated rise in oxidation of dihydroethidium that was prevented by Tempol or apocynin. To test whether H(2)O(2) might play a role, we examined its direct effects. From 1 to 100 μmol/l, H(2)O(2) contracted DVR whereas at 1 mmol/l it was vasodilatory. The H(2)O(2) scavenger polyethylene glycol-catalase reversed H(2)O(2) (10 μmol/l)-induced vasoconstriction; however, it did not affect l-NAME-induced contraction. Finally, the previously known rise in DVR permeability to (22)Na and [(3)H]raffinose that occurs with luminal perfusion was not prevented by NOS blockade. We conclude that intrinsic production of NO and ROS can modulate DVR vasoactivity and that l-NAME-induced vasoconstriction occurs, in part, by modulating superoxide concentration and not through H(2)O(2) generation. Intrinsic NO production does not affect DVR permeability to hydrophilic solutes.
AJP Renal Physiology 11/2010; 299(5):F1056-64. · 4.42 Impact Factor
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ABSTRACT: Oxidative stress is associated with vascular remodeling and increased preglomerular resistance that are both implicated in the pathogenesis of renal and cardiovascular disease. Angiotensin II induces superoxide production, which is metabolized by superoxide dismutase (SOD) or scavenged by NO. We investigated the hypothesis that SOD1 regulates renal microvascular remodeling, blood pressure, and arteriolar responsiveness and sensitivity to angiotensin II using SOD1-transgenic (SOD1-tg) and SOD1-knockout (SOD1-ko) mice. Blood pressure, measured telemetrically, rose more abruptly during prolonged angiotensin II infusion in SOD1-ko mice. The afferent arteriole media:lumen ratios were reduced in SOD1-tg and increased in SOD1-ko mice. Afferent arterioles from nontreated wild types had graded contraction to angiotensin II (sensitivity: 10(-9) mol/L; responsiveness: 40%). Angiotensin II contractions were less sensitive (10(-8) mol/L) and responsive (14%) in SOD1-tg but more sensitive (10(-13) mol/L) and responsive (89%) in SOD1-ko mice. Arterioles from SOD1-ko had 4-fold increased superoxide formation with angiotensin II at 10(-9) mol/L. N(G)-nitro-l-arginine methyl ester reduced arteriole diameter of SOD1-tg and enhanced angiotensin II sensitivity and responsiveness of wild-type and SOD1-tg mice to the level of SOD1-ko mice. SOD mimetic treatment with Tempol increased arteriole diameter and normalized the enhanced sensitivity and responsiveness to angiotensin II of SOD1-ko mice but did not affect wild-type or SOD1-tg mice. Neither SOD1 deficiency nor overexpression was associated with changes in nitrate/nitrite excretion or renal mRNA expression of NO synthase, NADPH oxidase, or SOD2/SOD3 isoforms and angiotensin II receptors. In conclusion, SOD1 limits afferent arteriole remodeling and reduces sensitivity and responsiveness to angiotensin II by reducing superoxide and maintaining NO bioavailability. This may prevent an early and exaggerated blood pressure response to angiotensin II.
Hypertension 09/2010; 56(5):907-13. · 6.21 Impact Factor
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ABSTRACT: Iodinated contrast media (CM) can potentially cause contrast-induced nephropathy (CIN). It is not clear, however, whether particular types of CM are more prone to cause CIN than others. In this study we compare 4 types of CM (ionic vs. nonionic; monomer vs. dimer) on their effects on the microvessels that supply the area at risk for renal damage in CIN (outer medullary descending vasa recta-DVR).
Using microdissection techniques, single DVR were isolated from rats and perfused using a set of concentric pipettes. After stabilization, perfusate was exchanged for a buffered solution containing either vehicle, or amidotrizoate (an ionic/monomeric CM), ioxaglate (an ionic/dimeric CM), iopromide (a nonionic/monomeric CM), and iodixanol (a nonionic/dimeric CM). The final iodine concentration was 23 mg iodine/mL, a concentration similar to that expected for coronary interventions. At this dilution, properties of CM solutions like viscosity and osmolarity are similar to the vehicle solution. To rule out further influence of CM-osmolarity and viscosity, the DVR bath solution was kept isoosmolar to the perfusate. Angiotensin II dose response curves were performed after the 20 minutes of perfusion. Digital videomicroscopy was used for measurements of luminal diameter.
All types of CM reduced luminal diameter of perfused DVR in a similar manner. After 20 minutes of perfusion, size of DVR were: 45% +/- 7% of initial diameter for the amidotrizoate-group; 53% +/- 6% for the ioxaglate-group; 63% +/- 11% for the iopromide-group; and 49% +/- 8% for the iodixanol-group. Control group remained at 96% +/- 4% of initial diameter. The angiotensin II dose response curves showed greater reactivity for amidotrizoate, iopromide and iodixanol, when compared with controls.
Under conditions where effects of osmolarity and viscosity are kept insignificant, perfusion of DVR using different types of iodinated CM leads to similar constriction of DVR. The response to angiotensin II was enhanced in 3 of the tested CM. This may be an important mechanism in the pathophysiology of CIN.
Investigative radiology 05/2010; 45(8):453-7. · 4.85 Impact Factor
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ABSTRACT: Many agents constrict isolated afferent arterioles only at concentrations higher than their physiological levels. Here we determined if norepinephrine, as released by sympathetic nerve activity, could influence the angiotensin II responsiveness of isolated mouse afferent arterioles. Pretreatment of the arterioles for short periods with norepinephrine significantly increased the ability of 10 picomolar angiotensin II to constrict the vessels, an effect inhibited by the alpha receptor blockers prazosin (alpha-1) or yohimbine (alpha-2). Although the intracellular calcium transients induced by angiotensin were not different, phosphorylation of the 20 kDa myosin light chain was significantly increased in the presence of norepinephrine. Phosphorylation of the p38 mitogen-activated protein kinase was not changed. Phosphorylation of the myosin phosphatase targeting subunit at Thr696, but not at Thr850, was significantly enhanced by, norepinephrine pretreatment, thus increasing the calcium sensitivity of the arteriolar smooth muscle. Our results show that norepinephrine increases afferent arteriolar sensitivity to angiotensin II by means of alpha receptor activation, causing increased calcium sensitivity through phosphorylation of the myosin phosphatase targeting subunit.
Kidney International 08/2009; 76(9):953-9. · 6.61 Impact Factor
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ABSTRACT: Nitric oxide (NO) modulates synaptic transmission, and its level is elevated during epileptic activity in animal models of epilepsy. However, the role of NO for development and maintenance of epileptic activity is controversial. We studied this aspect in rat organotypic hippocampal slice cultures and acute hippocampal-entorhinal cortex slices from wild-type and neuronal NO synthase (nNOS) knock-out mice combining electrophysiological and fluorescence imaging techniques. Slice cultures contained nNOS-positive neurons and an elaborated network of nNOS-positive fibers. Lowering of extracellular Mg(2+) concentration led to development of epileptiform activity and increased NO formation as revealed by NO-selective probes, 4-amino-5-methylamino-2',7'-difluorofluorescein and 1,2-diaminoanthraquinone sulfate. NO deprivation by NOS inhibitors and NO scavengers caused depression of both EPSCs and IPSCs and prevented initiation of seizure-like events (SLEs) in 75% of slice cultures and 100% of hippocampal-entorhinal cortex slices. This effect was independent of the guanylyl cyclase/cGMP pathway. Suppression of SLE initiation in acute slices from mice was achieved by both the broad-spectrum NOS inhibitor N-methyl-L-arginine acetate and the nNOS-selective inhibitor 7-nitroindazole, whereas inhibition of inducible NOS by aminoguanidine was ineffective, suggesting that nNOS activity was crucial for SLE initiation. Additional evidence was obtained from knock-out animals because SLEs developed in a significantly lower percentage of slices from nNOS(-/-) mice and showed different characteristics, such as prolongation of onset latency and higher variability of SLE intervals. We conclude that enhancement of synaptic transmission by NO under epileptic conditions represents a positive feedback mechanism for the initiation of seizure-like events.
Journal of Neuroscience 08/2009; 29(26):8565-77. · 7.11 Impact Factor
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ABSTRACT: To determine whether a type of contrast medium (CM), iodixanol, modifies outer medullary descending vasa recta (DVR) vasoreactivity and nitric oxide (NO) production in isolated microperfused DVR.
Animal handling conformed to the Animal Care Committee Guidelines of all participating institutions. Single specimens of DVR were isolated from rats and perfused with a buffered solution containing iodixanol. A concentration of 23 mg of iodine per milliliter was chosen to mimic that expected to be used in usual examinations in humans. Luminal diameter was determined by using video microscopy, and NO was measured by using fluorescent techniques.
Iodixanol led to 52% reduction of DVR luminal diameter, a narrowing that might interfere with passage of erythrocytes in vivo. Vasoconstriction induced by angiotensin II was enhanced by iodixanol. Moreover, iodixanol decreased NO bioavailability by more than 82%. Use of 4-hydroxy-2,2,6,6-tetramethylpiperidine 1-oxyl (a superoxide dismutase mimetic) prevented both vasoconstriction with iodixanol alone and increased constriction with angiotensin II caused by CM.
Iodixanol in doses typically used for coronary interventions constricts DVR, intensifies angiotensin II-induced constriction, and reduces bioavailability of NO. CM-induced nephropathy may be related to these events and scavenging of reactive oxygen species might exert a therapeutic benefit by preventing the adverse effects that a CM has on medullary perfusion.
Radiology 05/2009; 251(3):697-704. · 5.73 Impact Factor
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ABSTRACT: To determine the functional role of M(3) and M(5) muscarinic acetylcholine receptor subtypes in ophthalmic arteries using gene-targeted mice.
Muscarinic receptor gene expression was quantified in murine ophthalmic arteries using real-time PCR. To test the functional relevance of M(3) and M(5) receptors, ophthalmic arteries from mice deficient in either subtype (M3R(-/-), M5R(-/-), respectively) and wild-type controls were isolated, cannulated with micropipettes, and pressurized. Changes in luminal vessel diameter in response to muscarinic and nonmuscarinic receptor agonists were measured by video microscopy.
With the use of real-time PCR, all five muscarinic receptor subtypes were detected in ophthalmic arteries. However, mRNA levels of M(1), M(3), and M(5) receptors were higher than those of M(2) and M(4) receptors. In functional studies, after preconstriction with phenylephrine, acetylcholine and carbachol produced concentration-dependent dilations of ophthalmic arteries that were similar in M5R(-/-) and wild-type mice. Strikingly, cholinergic dilation of ophthalmic arteries was almost completely abolished in M3R(-/-) mice. Deletion of either M(3) or M(5) receptor did not affect responses to nonmuscarinic vasodilators such as bradykinin or nitroprusside.
These findings provide the first evidence that M(3) receptors are critically involved in cholinergic regulation of diameter in murine ophthalmic arteries.
Investigative ophthalmology & visual science 05/2009; 50(10):4822-7. · 3.43 Impact Factor
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ABSTRACT: Human glomerulonephritis (GN) is characterized by sustained proteinuria, sodium retention, hypertension, and edema formation. Increasing quantities of filtered protein enter the renal tubule, where they may alter epithelial transport functions. Exaggerated endocytosis and consequent protein overload may affect proximal tubules, but intrinsic malfunction of distal epithelia has also been reported. A straightforward assignment to a particular tubule segment causing salt retention in GN is still controversial. We hypothesized that 1) trafficking and surface expression of major transporters and channels involved in volume regulation were altered in GN, and 2) proximal tubular endocytosis may influence locally as well as downstream expressed tubular transporters and channels. Effects of anti-glomerular basement membrane GN were studied in controls and megalin-deficient mice with blunted proximal endocytosis. Mice displayed salt retention and elevated systolic blood pressure when proteinuria had reached 10-15 mg/24 h. Surface expression of proximal Na(+)-coupled transporters and water channels was in part [Na(+)-P(i) cotransporter IIa (NaPi-IIa) and aquaporin-1 (AQP1)] increased by megalin deficiency alone, but unchanged (Na(+)/H(+) exchanger 3) or reduced (NaPi-IIa and AQP1) in GN irrespective of the endocytosis defect. In distal epithelia, significant increases in proteolytic cleavage products of alpha-epithelial Na(+) channel (ENaC) and gamma-ENaC were observed, suggesting enhanced tubular sodium reabsorption. The effects of glomerular proteinuria dominated over those of blunted proximal endocytosis in contributing to ENaC cleavage. Our data indicate that ENaC-mediated sodium entry may be the rate-limiting step in proteinuric sodium retention. Enhanced proteolytic cleavage of ENaC points to a novel mechanism of channel activation which may involve the action of filtered plasma proteases.
American journal of physiology. Renal physiology 03/2009; 296(4):F902-11. · 3.68 Impact Factor
