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Background Gap junction channels made of Connexin37 (Cx37) are expressed by aortic endothelial and smooth muscle cells of hypertensive mice, as well as by the renin‐secreting cells of kidneys. Methods and Results To decipher whether Cx37 has any role in hypertension, angiotensin II (Ang II ) was infused in normotensive wild‐type and Cx37‐deficient mice (Cx37−/−). After 2 to 4 weeks, the resulting increase in blood pressure was lower in Cx37−/− than in wild‐type mice, suggesting an alteration in the Ang II response. To investigate this possibility, mice were submitted to a 2‐kidney, 1‐clip procedure, a renin‐dependent model of hypertension. Two weeks after this clipping, Cx37−/− mice were less hypertensive than wild‐type mice and, 2 weeks later, their blood pressure had returned to control values, in spite of abnormally high plasma renin levels. In contrast, Cx37−/− and wild‐type mice that received N ‐nitro‐ l ‐arginine‐methyl‐ester, a renin‐independent model of hypertension, featured a similar and sustained increase in blood pressure. The data indicate that loss of Cx37 selectively altered the Ang II ‐dependent pathways. Consistent with this conclusion, aortas of Cx37−/− mice featured an increased basal expression of the Ang II type 2 receptors ( AT 2R), and increased transcripts levels of downstream signaling proteins, such as Cnksr1 and Ptpn6 ( SHP ‐1). Accordingly, the response of Cx37−/− mice aortas to an ex vivo Ang II exposure was altered, since phosphorylation levels of several proteins of the Ang II pathway ( MLC 2, ERK , and AKT ) remained unchanged. Conclusions These findings provide evidence that Cx37 selectively influences Ang II signaling, mostly via a modulation of the expression of the Ang II type 2 receptor.

Functional zonation of the adrenal cortex is a consequence of the zone-specific expression of P450c17 ( CYP17A1) and its cofactors. Activin and inhibin peptides are differentially produced within the zones of the adrenal cortex and have been implicated in steroidogenic control. In this study, we investigated whether activin and inhibin can function as intermediates in functional zonation of the human adrenal cortex. Activin A suppressed CYP17A1 expression and P450c17 function in adrenocortical cell lines as well as in primary adrenal cell cultures. Inhibin βA-subunit mRNA and activin A protein levels were found to be increased up to 1,900-fold and 49-fold, respectively, after protein kinase C (PKC) stimulation through PMA or angiotensin II in H295R adrenocortical carcinoma cells. This was confirmed in HAC15 cells and for PMA in primary adrenal cell cultures. Both PMA and Ang II decreased CYP17A1 expression in the adrenocortical cell lines, whereas PMA concurrently suppressed CYP17A1 levels in the primary cultures. Inhibition of activin signaling during PKC stimulation through silencing of the inhibin βA-subunit or blocking of the activin type I receptor opposed the PMA-induced downregulation of CYP17A1 expression and P450c17 function. In contrast, PKA stimulation through adrenocorticotrophin or forskolin increased expression of the inhibin α-subunit and betaglycan, both of which are antagonists of activin action. These data indicate that activin A acts as a PKC-induced paracrine factor involved in the suppression of CYP17A1 in the zona glomerulosa and can thereby contribute to functional adrenocortical zonation.

Background Acute kidney injury (AKI) is a common and important complication of critical illness associated with increased morbidity, mortality and costs. Alterations in renal perfusion are thought to play a central role in its pathogenesis. This causal relationship remains, however, largely speculative as data on renal perfusion in AKI and critical illness are scarce. Indeed, methods enabling renal perfusion quantification are either invasive, expensive or inapplicable to critically ill patients. Contrast-enhanced ultrasonography (CEUS) is a recent imaging modality which provides a unique means of visualizing tissue perfusion. Studies have suggested that CEUS could enable blood flow quantification. CEUS would be an ideal tool in the intensive care unit (ICU) where knowledge of renal perfusion could help prevent or manage AKI. However, CEUS was never used nor validated in the ICU and its clinical use remains to be established. Hypothesis and specific aims We hypothesized that evaluation of renal microcirculation with CEUS was feasible and could change medical management in the ICU. To test this hypothesis, we have designed four studies with the following specific aims: 1. Validate preliminary results and improve technical measurements in a sheep model. 2. Demonstrate CEUS’s feasibility and safety in the ICU. Obtain preliminary results of renal microcirculation modifications associated with elective cardiac surgery. 3. Evaluate the impact of CEUS measurements in two clinical situations: a. Circulatory failure requiring noradrenaline infusion b. Type-1 hepato-renal syndrome requiring terlipressin treatment Overall methods and main results 1. In a sheep model in which renal blood flow could be modified pharmacologically and mechanically, we have compared CEUS-derived parameters to measurements of a an implanted flow probe. We found that CEUS derived parameters were highly heterogeneous and that they did not parallel changes in renal blood flow. Technical measurements were improved and simpler protocols designed for further studies. 2. We have performed CEUS studies before and after an elective cardiac surgery in twelve patients. This study was the first attempt to quantify renal microcirculation in critically ill patients and has demonstrated CEUS’s safety and feasibility in ICU. 3. We have compared changes in CEUS-derived parameters under two levels of blood pressure (BP) in twelve patients with circulatory shock. We have established that microcirculatory response to an increase in BP as assessed by CEUS was highly heterogeneous and unpredictable. This finding is consistent with data from large trials and suggest that a CEUS-guided strategy to determine ideal target BP could be tested. 4. We have compared changes in CEUS-derived parameters before and after the administration of terlipressin in four patients with type-1 hepato-renal syndrome. We found dramatic changes in CEUS-derived parameters after terlipressin therapy and perfusion responses appeared variable. Larger studies are necessary to establish the sensitivity and specificity of CEUS to predict terlipressin responsiveness. Conclusions CEUS is safe and feasible in the intensive care unit. CEUS-derived perfusion indices might not fully correlate with renal blood flow as they are indicative of renal microcirculation changes. Further studies are required to establish the significance of CEUS-derived indices changes in clinical practice.

The rat portal vein is a useful pharmacological model to study the contractions of smooth muscle cells through both receptor-dependent and receptor-independent mechanisms. We previously showed that sepsis decreases the spontaneous and agonist-induced contractile response to angiotensin II in this model. To determine whether acidosis and hyperthermia, which occur in sepsis, might contribute to this vascular failure, rat portal veins were isolated from control rats and exposed to norepinephrine and angiotensin II. During the pharmacological tests, the rat portal vein were incubated at 37 or 39.5 degrees C or infused with a solution at low pH with normal or high pCO(2). Mild and severe acidosis had minor effects on the vascular response of rat portal vein to norepinephrine and angiotensin II. In contrast, hyperthermia decreased the response of both drugs. Nitric oxide (NO), carbon monoxide (CO), and prostaglandins were not responsible for the decreased response. Thus, acidosis observed during sepsis is not responsible for the vascular dysfunction of rat portal vein. In contrast, hyperthermia participates to the vascular failure but the mediator responsible remains unknown.

We carried out semiquantitative immunoblotting of kidney to identify apical sodium transporter proteins whose abundances are regulated by angiotensin II. In NaCl-restricted rats (0.5 mEq Na/200 g BW/d), the type 1 angiotensin II receptor (AT 1 receptor) antagonist, candesartan, (1 mg/kg of body weight per day SC for 2 days) markedly decreased the abundance of the α subunit of the epithelial sodium channel (ENaC). This subunit has been shown to be rate-limiting for assembly of mature ENaC complexes. In addition, systemic infusion of angiotensin II increased αENaC protein abundance in rat kidney cortex. The decrease in αENaC protein abundance in response to AT 1 receptor blockade was associated with a fall in αENaC mRNA abundance (real-time RT-PCR), consistent with transcriptionally mediated regulation. The effect of AT 1 receptor blockade on αENaC expression was not blocked by spironolactone, suggesting a direct role of the AT 1 receptor in regulation of αENaC gene expression. Candesartan administration was also found to increase the abundances of the β and γ subunits. The increase in β and γENaC protein abundance was not associated with a significant increase in the renal abundances of the corresponding mRNAs, suggesting a posttranscriptional mechanism. Immunocytochemistry confirmed the increase in β and γENaC protein abundance and demonstrated candesartan-induced ENaC internalization in collecting duct cells. The results support the view that the angiotensin II receptor regulates ENaC abundance, consistent with a role for angiotensin II in regulation of collecting duct function.

This study approaches the question of whether angiotensin II (AngII) and transforming growth factor beta (TGF-beta) are important mediators for mesangial heparan sulfate proteoglycan (HSPG) production. This might explain the beneficial effects of angiotensin-converting enzyme inhibitors observed in several kidney diseases independent from their hemodynamic effects. Metabolic-labeling studies revealed that AngII induced a decrease of HSPG synthesis with decreases in N-sulfation of the glycosaminoglycan side chains. ELISA measurements with a heparan sulfate (HS)-specific monoclonal antibody confirmed that AngII decreased HS production. AngII increased TGF-beta production in a dose-dependent fashion. Specific mRNA for the large basement membrane HSPG (perlecan) decreased, whereas mRNA for TGF-beta increased after incubation with AngII. Blockade of the Subtype 1 Ang-II receptor (ATR1) reversed both the effects of AngII on HSPG and TGF-beta production. Coincubation of the mesangial cells with neutralizing antibodies against TGF-beta significantly reduced the production of HS as compared with control and AngII. These results indicate that the decrease in HS synthesis induced by AngII is not mediated by an increase in TGF-beta, but on the contrary, the increase in TGF-beta partially counteracts the inhibition of HS production by AngII. Considering the important role of HSPG in maintaining the glomerular charge barrier, cell proliferation, and matrix interaction, downregulation of the production of this molecule by increased local AngII concentrations could have important consequences, such as albuminuria and matrix expansion.

International audience; Pathophysiological aldosterone (aldo)/mineralocorticoid receptor (MR) signaling has significant effects on the cardiovascular system, resulting in hypertension and cardiovascular remodeling; however, the specific contribution of the vascular MR to blood pressure regulation remains to be established. To address this question, we generated a mouse model with conditional overexpression of the MR in endothelial cells (MR-EC). In basal conditions, MR-EC mice developed moderate hypertension that could be reversed by canrenoate, a pharmacological MR antagonist. MR-EC mice presented increased contractile response of resistance arteries to vasoconstrictors (phenylephrine, thromboxane A(2) analog, angiotensin II, and endothelin 1) in the absence of vascular morphological alterations. The acute blood pressure response to angiotensin II or endothelin 1 infusion was increased in MR-EC mice compared with that in littermate controls. These observations demonstrate that enhanced MR activation in the endothelium generates an increase in blood pressure, independent of stimulation of renal tubular Na(+) transport by aldo/MR or direct activation of smooth muscle MR and establish one mechanism by which endothelial MR activation per se may contribute to impaired vascular reactivity.

Hint2 belongs to the superfamily of histidine triad hydrolase enzymes. Recently, it has been shown to influence the mitochondria-dependent apoptosis occurring in hepatocytes, but its mechanism of action is still obscure. Here, we demonstrate that Hint2 is expressed in the mitochondria of H295R cells and in normal adrenals, and that this protein is involved in steroidogenesis. The presence of Hint2 in H295R cells was revealed by RT-PCR and by immunoblot analysis of subcellular fractions. The protein appeared associated with mitochondrial membranes, probably facing the interior of the organelle. Hint2 overexpression in H295R cells had no effect on pregnenolone secretion elicited by angiotensin II or K+, whereas protein silencing with specific small interfering RNA resulted in a marked reduction of the steroidogenic response. The duration of the mitochondrial calcium signal induced by angiotensin II was also reduced upon Hint2 down-regulation with small interfering RNA, but not affected after its overexpression, suggesting that under basal conditions, Hint2 is optimally expressed, and not rate limiting in steroidogenesis. Moreover, Hint2 also appeared involved in Ca2+-independent pathways leading to steroid formation. Indeed, pregnenolone formation in response to either forskolin or a hydroxyl analog of cholesterol was markedly reduced after Hint2 silencing. Calcium-dependent and calcium-independent actions of Hint2 on steroidogenesis could be related to its ability to maintain a favorable mitochondrial potential. In conclusion, these data suggest that, in H295R cells, Hint2 is required for an optimal steroidogenic response, possibly because of a particular signalling function exerted within the mitochondria and that still remains to determine at the molecular level.

In this study we have examined the subcellar pathways along which angiotensin II (ANG II) causes renal vasoconstriction. Using the isolated perfused rat kidney model, we found that renal vasoconstriction produced by ANG II (100 pM) was not altered by the calmodulin antagonists calmidazolium (1 microM) and N-(6-aminohexyl)-5-chloro-1-naphthalensulfonamide (W-7, 10 microM) but was blunted by staurosporine (100 nM) and 1-(5-isoquinolinylsulfonyl)-2-methyl-piperazine (H-7, 50 microM), two structurally distinct putative protein kinase C inhibitors. The phorbol ester 4 alpha-phorbol 12,13-didecanoate (1-100 nM) did not alter renal vascular resistance, whereas phorbol 12-myristate 13-acetate (PMA, 1-100 nM) caused potent and dose-dependent vasoconstriction that was prevented by staurosporine (100 nM) and H-7 (50 microM). The vasoconstrictory effects of ANG II and PMA were attenuated by the calcium channel blockers verapamil (5 microM) and nifedipine (5 microM) and were reversibly inhibited when cobaltous chloride (2 mM) was added to the perfusate. Taken together, our findings support the concept that the renal vasoconstrictory effect of ANG II is essentially mediated by protein kinase C activation, which either requires or enhances the entrance of extracellular calcium.

We have previously demonstrated that exercise training prevents the development of Angiotensin (Ang) II-induced atherosclerosis and vulnerable plaques in Apolipoprotein E-deficient (ApoE-/-) mice. In this report, we investigated whether exercise attenuates progression and promotes stability in pre-established vulnerable lesions. To this end, ApoE-/- mice with already established Ang II-mediated advanced and vulnerable lesions (2-kidney, 1-clip [2K1C] renovascular hypertension model), were subjected to sedentary (SED) or voluntary wheel running training (EXE) regimens for 4 weeks. Mean blood pressure and plasma renin activity did not significantly differ between the two groups, while total plasma cholesterol significantly decreased in 2K1C EXE mice. Aortic plaque size was significantly reduced by 63% in 2K1C EXE compared to SED mice. Plaque stability score was significantly higher in 2K1C EXE mice than in SED ones. Aortic ICAM-1 mRNA expression was significantly down-regulated following EXE. Moreover, EXE significantly down-regulated splenic pro-inflammatory cytokines IL-18, and IL-1β mRNA expression while increasing that of anti-inflammatory cytokine IL-4. Reduction in plasma IL-18 levels was also observed in response to EXE. There was no significant difference in aortic and splenic Th1/Th2 and M1/M2 polarization markers mRNA expression between the two groups. Our results indicate that voluntary EXE is effective in slowing progression and promoting stabilization of pre-existing Ang II-dependent vulnerable lesions by ameliorating systemic inflammatory state. Our findings support a therapeutic role for voluntary EXE in patients with established atherosclerosis.

International audience; To understand the role of the superoxide-generating NADPH oxidase NOX1 in the vascular system, we have generated NOX1-deficient mice. NOX1-deficient mice had a moderately decreased basal blood pressure. In response to angiotensin II they showed an almost complete loss of the sustained blood pressure response, while the initial increase was conserved. NOX1-deficient mice showed a marked reduction in aortic media hypertrophy. Angiotensin II-induced smooth muscle cell proliferation was conserved, but there was a marked decrease in extracellular matrix accumulation. Our results establish a role for NOX1 in blood pressure regulation and vascular angiotensin II response.

Background/Aims: The portal vein has spontaneous and agonist-induced contractile activities and whether sepsis alters these two types of contractile activities is unknown. Methods: To study the effect of sepsis on the spontaneous contractile activity and the contractile responses to norepinephrine (NE), angiotensin II (AT II ), and neurokinin B (NKB) in the rat portal vein (RPV), we performed a cecal ligature and puncture (CLP) 24 h before RPV isolation. Results: CLP decreased the spontaneous activity and induced hyporesponsiveness to AT II and NKB. The vascular failure was correlated to the severity of sepsis. In contrast, the reactivity to NE was not altered. Although inducible NO synthase was detected in RPV isolated from CLP rats, NO synthase inhibitors did not restore either the responsiveness to AT II and NKB or the spontaneous activity. Additionally, hyporesponsiveness to AT II and NKB was not modified by indomethacin. Conclusions: CLP decreases the spontaneous activity of the RPV as well as the contractile responses to AT II and NKB. The vascular failure is correlated to the severity of sepsis. The reactivity to NE is not altered in this model. Neither NO nor prostaglandins are responsible for the vascular abnormalities observed during CLP.

Cells from primary cultures of four glioblastomas (GB), three low-grade astrocytomas (A), and four low-grade oligodendrogliomas (O) were tested for the presence of neuroligand receptors linked to Ca2+ signalling by calcium imaging. Cells of days 3 to 21 in culture were incubated with 5 microM fluo-3-acetomethylester in a bath solution and stimulated with 0.1 mM ATP, 0.01 mM angiotensin II, bradykinin, histamine, norepinephrine, serotonin, and substance P for 15 s, with 0.01 mM glutamate and 50 mM K+ for 30 s. Changes in the Ca2+ concentration were measured with a confocal laser scanning microscope. In all glioma subtypes, the majority of cells showed Ca2+ responses after application of histamine (60% of cells tested in GB, 67% in A, 86% in O), bradykinin (66% in GB, 29% in A, 55% in O) and ATP (48% in GB, 70% in A, 47% in O). The other stimuli induced Ca2+ transients in a smaller proportion (between 33% and 2%) of the cells. Our study demonstrates that histamine, bradykinin and ATP are potent inducers of [Ca2+]i signals in gliomas. Neurosci Lett

As angiotensin-converting enzyme inhibition is accompanied by a marked decrease in glomerular protein loss, the hypothesis was tested that an increase of the glomerular transcapillary hydraulic pressure difference by exogenous angiotensin II would increase microalbuminuria in patients with insulin (IDDM) and non-insulin-dependent diabetes mellitus (NIDDM). Acute effects of increasing doses of angiotensin II (1, 3 and 6 ng/kg/min) were studied on mean arterial pressure (MAP), glomerular filtration rate (GFR), effective renal plasma flow (ERPF), filtration fraction (FF), total renal vascular resistance (TRVR), and urinary albumin excretion rate (UAER) in 11 IDDM and 11 NIDDM microalbuminuric patients. Angiotensin II infusion changed MAP from 100 +/- 3 mmHg at baseline to 105 +/- 3, 111 +/- 3, and 116 +/- 3 mmHg (P < 0.001), ERPF from 542 +/- 29 to 478 +/- 24, 429 +/- 23, and 382 +/- 19 ml/min (P < 0.001), FF from 20.2 +/- 0.06 to 23.1 +/- 0.7, 27.1 +/- 1.1, and 29.8 +/- 1.2% (P < 0.001), and TRVR from 9454 +/- 809 to 11,158 +/- 930, 13,310 +/- 1206, and 15,538 +/- 1362 dyne s cm-5 (P < 0.001). GFR and UAER, however, did not change significantly. Therefore, during angiotensin II infusion ERPF decreased, while FF and TRVR increased. As UAER and GFR remained unchanged, the presumed rise in intraglomerular capillary pressure by exogenous angiotensin II did not increase UAER. We suggest that during manipulation of the renin-angiotensin system, as in other renal diseases with proteinuria, factors other than glomerular transcapillary hydraulic pressure determine the degree of urinary albumin loss in microalbuminuric IDDM and NIDDM patients.

This study approaches the question of whether angiotensin II (AngII) and transforming growth factor beta (TGF-beta) are important mediators for mesangial heparan sulfate proteoglycan (HSPG) production. This might explain the beneficial effects of angiotensin-converting enzyme inhibitors observed in several kidney diseases independent from their hemodynamic effects. Metabolic-labeling studies revealed that AngII induced a decrease of HSPG synthesis with decreases in N-sulfation of the glycosaminoglycan side chains. ELISA measurements with a heparan sulfate (HS)-specific monoclonal antibody confirmed that AngII decreased HS production. AngII increased TGF-beta production in a dose-dependent fashion. Specific mRNA for the large basement membrane HSPG (perlecan) decreased, whereas mRNA for TGF-beta increased after incubation with AngII. Blockade of the Subtype 1 Ang-II receptor (ATR1) reversed both the effects of AngII on HSPG and TGF-beta production. Coincubation of the mesangial cells with neutralizing antibodies against TGF-beta significantly reduced the production of HS as compared with control and AngII. These results indicate that the decrease in HS synthesis induced by AngII is not mediated by an increase in TGF-beta, but on the contrary, the increase in TGF-beta partially counteracts the inhibition of HS production by AngII. Considering the important role of HSPG in maintaining the glomerular charge barrier, cell proliferation, and matrix interaction, downregulation of the production of this molecule by increased local AngII concentrations could have important consequences, such as albuminuria and matrix expansion.

In this study we examined the role of calcium ions in the control of renin release by the renal artery pressure. For this purpose renin secretion rates (RSR) were measured in isolated rat kidneys perfused at pressures of 140, 100, 80 and 40 mmHg (19, 13, 11, 5 kPa) with media containing either 1.5 mmol/l ("normal") or zero calcium concentrations (calcium-free perfusate with 0.5 mmol/l EGTA). At normal calcium the RSR was inversely related to the renal artery pressure, whereas calcium withdrawal resulted in an almost linear and proportional relationship between RSR and perfusion pressure. As a consequence, RSR at 140 mm Hg (19 kPa) with a calcium-free medium was similar to renin release at 40 mm Hg (5 kPa) with normal calcium. The nitric oxide (NO) donor sodium nitroprusside (1 mumol/l) stimulated RSR in a pressure-dependent fashion at a calcium concentration of 1.5 mmol/l. With a calcium-free perfusate, sodium nitroprusside did not restore the inverse pressure dependence of RSR seen with normal calcium but almost doubled the RSR across the whole pressure range. Whilst RSR was significantly reduced by angiotensin II (1 nmol/l) in the range between 40 mmHg and 140 mmHg (5-19 kPa) with normal calcium, withdrawal of extracellular calcium ions practically abolished the inhibitory action of angiotensin II. Since angiotensin II attenuated RSR especially at low renal perfusion pressure, our results indicate that renin release in this pressure range is still inhibitable by calcium mobilization in renal juxtaglomerular cells. Thus, the enhancement of renin secretion at lower pressures cannot be explained by a decreased sensitivity of renin release towards calcium ions.(ABSTRACT TRUNCATED AT 250 WORDS)

We investigated the relevance of anions for the regulation of renin secretion from the kidneys. For this purpose we measured renin release from isolated rat kidneys that were perfused with medium containing either 120 mmol/l (normal) chloride or 95 mmol/l of isethionate, acetate, or nitrate anions in exchange for equimolar amounts of chloride. Lowering the extracellular chloride concentration by either of these maneuvers significantly enhanced renin secretion rates (RSR) at a perfusion pressure of 100 mmHg. Increasing pressure above 100 mmHg inhibited renin release in the presence of isethionate and acetate but not with nitrate anions. The renin stimulatory effects of isethionate and acetate but not that of nitrate anions disappeared in the presence of bumetanide (100 mumol/l), an inhibitor of macula densa chloride transport. Activation of renin secretion by isethionate and acetate was blunted with 100 pmol/l angiotensin II (ANG II), whereas tenfold higher concentrations of ANG II were required to attenuate the effect of nitrate ions. The amount of renin released in the presence of nitrate was fully additive to RSR values obtained with maximally effective doses of isoproterenol. These findings are consistent with the idea that impermeant anions such as isethionate and acetate enhance renin secretion from the kidneys predominantly via the tubular macula densa mechanism. The stimulatory influence of membrane-permeable nitrate anions appears to involve additional pathways and is mediated by a decreased calcium sensitivity of the renin secretory process rather than resulting from an adenosine 3',5'-cyclic monophosphate-dependent action.

1. We have examined whether an increase of renal vascular resistance is generally accompanied by an inhibition of renin secretion. The effects of vasoconstriction produced by angiotensin II (Ang II), arginine-vasopressin (AVP), and potassium (KCl) depolarization on vascular resistance and on renin release from isolated rat kidneys perfused at constant pressure of 100 mmHg were investigated. 2. Histological examination performed on some representative kidneys revealed that the tubular lumina of all segments within the cortex were patent and the brush borders of the proximal tubules were well preserved. The renal vasculature and the juxtaglomerular region appeared to be morphologically intact. By immunocytochemistry, renin-positive cells were found exclusively in the wall of the afferent arterioles. 3. Basal flow rate through isolated kidneys was 14.5 +/- 2.0 ml min-1 (g kidney weight (gkw))-1 (mean +/- S.E.M., n = 10). Under control conditions renin secretory rates were in the range of 30-40 (ng Ang I h-1) min-1 gkw-1. 4. Ang II (100 pM) caused a decrease of renal flow rate to 42 +/- 2% of control which was accompanied by a reduction of renin secretion rates by a factor of 4. 5. AVP (10 pM to 1 nM) reduced renal perfusate flow in a dose-dependent fashion to a minimum of 25 +/- 3% of control. The vasoconstrictor effect of AVP was paralleled by a concentration-dependent increase of renin secretory rates reaching a factor of maximally 5 when AVP was used at a concentration of 1 nM. The stimulatory effect of AVP on renin release could be mimicked by [deamino-Cys1, D-Arg8]-vasopressin (dDAVP), a vasopressin analogue with prevalent V2 receptor agonistic properties. In the presence of dDAVP (100 nM, 1 microM) renal flow rate reversibly increased by 8 and 12% of control values, respectively. 6. Depolarizing concentrations of KCl (30 mM) decreased perfusate flow to 20 +/- 4% of control. The vasoconstrictor effect of KCl was paralleled by an increase of the arterio-venous difference of perfusate renin activity to such an extent that the rate of renin release remained unaltered. 7. Our findings suggest that there exists no general inverse relationship between renal arteriolar resistance and renin secretion. Our study, moreover, does not support a functional role of potential operated calcium channels in the control of renin secretion. Finally, we conclude that V2 receptors are present on juxtaglomerular epithelioid cell membranes and mediate the stimulatory effect of AVP on renin release from isolated rat kidneys.

The influence of the fungoid undecapeptide cyclosporin A (CyA) on PGE2 release from cultured rat aortic smooth muscle cells was investigated in this study. We found that CyA time and concentration dependently (ED50:500 ng/ml) inhibited PGE2 release from the cells. CyA attenuated both basal and PGE2 release evoked by angiotensin II (10(-10)-10(-6) M), arginine vasopressin (10(-10)-10(-6) M) and ionomycin (10(-9)-10(-6) M). CyA (1 microgram/ml) did not affect the conversion of exogenous arachidonic acid (1 microM) into PGE2. The inhibitory effect of CyA was neutralized by high concentrations of the calcium ionophore ionomycin (greater than 3 X 10(-6) M). Taken together our results indicate that CyA inhibits both basal and vasoconstrictor evoked PGE2 release from vascular smooth muscle by impairing the availability of free arachidonic acid rather than by inhibiting the conversion of arachidonic acid into PGE2.

Renal mesangium is a target for calcitonin gene-related peptide. Rat calcitonin gene-related peptide (CGRPα; EC50, 1 nM) was shown to stimulate cAMP formation in cultured rat renal mesangial cells. CGRP concentration dependently (EC50, 1 nM) also inhibited contraction of mesangial cells by angiotensin II (10 nivi). Angiotensin II (10nM) caused a transient increase of the intracellular calcium concentration from 140nM to 480nM in the mesangial cells, but these calcium transients were not altered by CGRP. CGRP (10 nM) decreased vascular resistance in the isolated rat kidney perfused at constant pressure (100mm Hg; P < 0.01). The decreased vascular resistance was accompanied by a rise of the glomerular filtration fraction. CGRP, moreover, attenuated the effects of angiotensin II on renal vascular resistance and glomerular filtration (P < 0.01). In conclusion, CGRP causes relaxation of renal mesangial cells and decreases renal vascular resistance. As a result CGRP raises glomerular filtration and the filtration fraction. The effect may be linked to cyclic AMP formation. Thus, regulation of renal vascular and glomerular function may represent a novel action of CGRP apart from its cardiovascular effects.

It was the aim of the present study to get insight into some of the intracellular mechanisms by which the vasoconstrictor hormones angiotensin II (ANG II), arginine vasopressin (AVP), and norepinephrine (NE) inhibit renin release from renal juxtaglomerular cells. To this end a primary cell culture from rat renal cortex was established that consisted of 50% juxtaglomerular cells. The cultured juxtaglomerular cells contained prominent renin granules closely resembling those in the intact kidney and responded to a number of stimuli of renin release. By using these cultures, we found that ANG II (10(-7) M), AVP (10(-6) M), and NE (10(-5) M) inhibited renin release and increased the calcium permeability of the plasma membrane of the cultured cells. Both the effects on renin release and on calcium permeability could be diminished or even be abolished by the calcium channel blocker verapamil (Vp) (10(-5) M). ANG II, AVP, and NE led to an increased formation of diacylglycerol (DAG), a well-known stimulator of protein kinase C (PKC). Moreover, a direct stimulation of PKC by 12-O-tetradecanoylphorbol-13-acetate (TPA) (10(-8)-10(-6) M) also inhibited renin release and increased the calcium permeability of the cell membrane. Similar to ANG II, AVP, and NE, the effects of TPA on calcium permeability and renin release could be diminished by Vp. In conclusion, these results point toward a common mechanism by which vasoconstrictors inhibit renin release from renal juxtaglomerular cells: ANG II, AVP, and NE activate a phospholipase C, which generates DAG.(ABSTRACT TRUNCATED AT 250 WORDS)

The cardiovascular and endocrine profile of cromakalim has been studied in 8 healthy men (age 25 +/- 2 years: means SEM) and its influence on renin release from cultured rat juxtaglomerular cells in vitro has also been examined. According to a double-blind, randomized sequence the subjects received placebo or cromakalim 1 mg as a single daily oral dose for 5 days. Compared to placebo, cromakalim significantly increased plasma renin activity (+ 122%; from 1.73 to 3.87 ng AI.ml-1.h-1), angiotensin II (+ 105%; from 5.1 to 10.5 pg.ml-1), and norepinephrine (+ 61%) levels, and heart rate (+ 8%). Plasma aldosterone, blood pressure and indices of the electrolyte-fluid volume state were unchanged. Cromakalim in vitro stimulated renin release, from 9.9 to 36.5 ng AI.h-1.30 min.mg cell protein, from juxtaglomerular cells. It appears that the presumed K+-channel activator cromakalim increases renin release in vivo at least in part by direct stimulation of renal juxtaglomerular cells.

Strips of granulation tissue from three different experimental models contract in vitro when treated with substances that induce contraction of smooth muscle. Because the fibroblasts in such tissues have some ultrastructural features typical of smooth muscle, our findings indicate that fibroblasts are able to modulate toward a cell type that is morphologically and functionally close to smooth muscle.