Pressure-dependent renin release during chronic blockade of nitric oxide synthase

Classical Renin-Angiotensin system in kidney physiology

The renin-angiotensin system has powerful effects in control of the blood pressure and sodium homeostasis. These actions are coordinated through integrated actions in the kidney, cardiovascular system and the central nervous system. Along with its impact on blood pressure, the renin-angiotensin system also influences a range of processes from inflammation and immune responses to longevity. Here, we review the actions of the "classical" renin-angiotensin system, whereby the substrate protein angiotensinogen is processed in a two-step reaction by renin and angiotensin converting enzyme, resulting in the sequential generation of angiotensin I and angiotensin II, the major biologically active renin-angiotensin system peptide, which exerts its actions via type 1 and type 2 angiotensin receptors. In recent years, several new enzymes, peptides, and receptors related to the renin-angiotensin system have been identified, manifesting a complexity that was previously unappreciated. While the functions of these alternative pathways will be reviewed elsewhere in this journal, our focus here is on the physiological role of components of the "classical" renin-angiotensin system, with an emphasis on new developments and modern concepts.

Effects of Chronic Nitric Oxide Inhibition on the Renal Excretory Response to Leptin

OBJECTIVE

Previous investigations have demonstrated that leptin promotes natriuresis with a renal tubular effect. However, the mechanisms involved in this response are unclear. The present study was designed to examine the hypothesis that the natriuretic response to leptin in normotensive Sprague-Dawley rats is regulated by nitric oxide (NO).

RESEARCH METHODS AND PROCEDURES

The hemodynamic and renal excretory effects of intravenous bolus administration of pharmacological doses of synthetic murine leptin were examined in groups of control Sprague-Dawley rats (n = 8), Sprague-Dawley rats treated for 4 days with the NO synthase inhibitor Nomega-nitro-L-arginine methyl ester (L-NAME) (n = 8), and Sprague-Dawley rats treated for 4 days with L-NAME followed by acute treatment with sodium nitroprusside (n = 8).

RESULTS

In the control group (n = 8), an intravenous bolus of leptin, 400 microg/kg body weight, increased urinary sodium excretion 4- to 6-fold. In the Sprague-Dawley rats chronically administered l-NAME (n = 8), an intravenous bolus of 400 microg/kg of leptin did not increase sodium excretion. Acute sodium nitroprusside infusion to Sprague-Dawley rats chronically treated with L-NAME (n = 8) was associated with partial restoration of the sodium excretory response to leptin administration.

DISCUSSION

Collectively, these results are interpreted to suggest that the natriuretic and diuretic responses to leptin observed in the Sprague-Dawley rat require a functional NO system.

Effect of Nitric Oxide Synthase Inhibition and Saline Administration on Blood Pressure and Renal Sodium Handling During Experimental Sepsis in Rats

Much effort has been made in recent years to clarify metabolic and renal function changes in sepsis. A number of studies performed in different models of sepsis have been described. One such model that is frequently used is cecal ligation and puncture (CLP) in rats. This model resembles human sepsis in several important aspects, such as an early phase of hyperdynamic, hypermetabolic sepsis followed by a late hypodynamic, hypometabolic phase. The present study evaluated the blood pressure (n = 5) and renal function changes during development of CLP renal failure and to determine the effects of NOS inhibition (L-NAME) and 0.15 M NaCl administration on tail blood pressure and renal function in randomly assigned five groups (n = 10 each): (1) Sham-operated, (2) Sham-operated L-NAME-treated, (3) CLP rats, (4) CLP L-NAME-treated, and (5) CLP 0.15 M NaCl-treated rats. The basal tail blood pressure was not significantly different among the four groups. One week later, arterial pressure was significantly increased in sham-operated L-NAME-treated rats (159 +/- 12 mmHg) compare with the other groups (118 +/- 9.0 mmHg in nontreated rats, p < 0.05). Blood pressure shows a slightly and not significant decrease up to 12h in L-NAME and 0.15 M NaCl treated rats, which in turn was followed by a significant reduced arterial pressure 18h after CLP in both groups (L-NAME: 96.0 +/- 3.6 mmHg, p < 0.05) and NaCl: 82.3 +/- 2.4 mmHg, p < 0.05) compared to sham-operated groups. The glomerular filtration rate estimated by CCr decreases significantly in the CLP untreated group (p < 0.001) and did not significantly differ from the sham-operated and L-NAME-treated groups (p = 0.4) during the studies of renal tubule sodium handling. On the other hand, subcutaneous 0.15 M NaCl administration prevented CCr decreases in CLP rats (p = 0.25). CLP increased the FENa in the sham-operated from: 857.2 +/- 85.1 delta%min(-1) to CLP: 1197.8 +/- 119.0 delta%min(-1). The high FENa to CLP was blunted and significantly reduced by previous systemic treatment of animals with L-NAME from sham-operated+L-NAME: 1368.0 +/- 72.0 delta%min(-1) to CLP+L-NAME: 1148.0 +/- 60.4 delta%min(-1) (p < 0.01). The enhanced FENa in the CLP group were accompanied by a significant increase in proximal sodium reabsorption rejection. The salient findings of the present study suggest that a decrease in the blood pressure and creatinine clearance caused by CLP may benefit from L-NAM and fluid resuscitation during initial bacteremia (first 12 h) by promoting an additional increase of tubule sodium reabsorption in the post-proximal segments of nephrons, but these therapies could not prevent acute renal failure after established endotoxemia.

Regulation of renin release by local and systemic factors

The renin-angiotensin system (RAS) is critically involved in the regulation of the salt and volume status of the body and blood pressure. The activity of the RAS is controlled by the protease renin, which is released from the renal juxtaglomerular epithelioid cells into the circulation. Renin release is regulated in negative feedback-loops by blood pressure, salt intake, and angiotensin II. Moreover, sympathetic nerves and renal autacoids such as prostaglandins and nitric oxide stimulate renin secretion. Despite numerous studies there remained substantial gaps in the understanding of the control of renin release at the organ or cellular level. Some of these gaps have been closed in the last years by means of gene-targeted mice and advanced imaging and electrophysiological methods. In our review, we discuss these recent advances together with the relevant previous literature on the regulation of renin release.

Cardiovascular homeostasis in hypotension associated with initial stages of severe acute pancreatitis

OBJECTIVES

To identify the mechanisms underlying hypotension during the early phase of severe acute pancreatitis (SAP) by analyzing whether an impaired response to vasoactive substances occurs in this pathological process.

METHODS

Experimental SAP was induced by infusing 5% sodium taurocholate through the main pancreatic duct in rats. Once mean arterial pressure (MAP) in animals with pancreatitis was reduced, different vasoactive substances and inhibitors were administered.

RESULTS

Administration of the nonspecific nitric oxide synthase inhibitor N omega-nitro-L-arginine methyl ester caused a similar increase in MAP in rats with pancreatitis and control rats, whereas inducible nitric oxide synthase inhibition did not cause changes in MAP. Moreover, the hypertensive response to endothelin and angiotensin II was lower in pancreatitis. Inhibition of angiotensin II synthesis by the angiotensin-converting enzyme inhibitor perindopril in animals with pancreatitis caused severe hypotension, causing death in 40% of them. Finally, pressor hyporesponsiveness to angiotensin II in animals with pancreatitis was avoided by previous administration of perindopril and N omega-nitro-L-arginine methyl ester.

CONCLUSIONS

The SAP-induced hypotension is associated with a deficient pressor responsiveness to angiotensin II and endothelin-1. The renin-angiotensin system plays an important role in the control of MAP in animals with pancreatitis.

NO and cGMP mediate angiotensin AT2 receptor-induced renal renin inhibition in young rats

We hypothesized that angiotensin subtype-2 receptor (AT(2)R) inhibits renal renin biosynthesis in young rats via nitric oxide (NO). We monitored changes in renal NO, cGMP, renal renin content (RRC), and ANG II in 4-wk-old rats in response to low sodium (LNa(+)) intake alone and combined with 8-h direct renal cortical administration of AT(1) receptor blocker valsartan (VAL), AT(2)R blocker PD123319 (PD), NO synthase inhibitor N(G)-nitro-l-arginine methyl ester (l-NAME), NO donor S-nitroso-N-acetyl penicillamine (SNAP), or guanylyl cyclase inhibitor 1H-[1,2,4] oxadiazolo[4,2-alpha] quinoxaline-1-one (ODQ). In addition, we monitored renal endothelial nitric oxide synthase (eNOS) and neuronal nitric oxide synthase (nNOS) in response to VAL or PD. LNa(+), VAL, PD, l-NAME, and ODQ increased RRC, ANG II, and renin mRNA. PD and l-NAME decreased NO and cGMP, while SNAP reduced RRC, ANG II, renin mRNA, and reversed the effects of PD. PD also reduced eNOS and nNOS protein and mRNA. Combined treatment with PD, l-NAME, or ODQ and VAL reversed the effects of VAL and caused further increase in RRC, ANG II, renin mRNA, and protein. ODQ reversed the effects of SNAP. These data demonstrate that the renal AT(2) receptor decreases renal renin biosynthesis and ANG II production in young rats. Reversal of the PD effects by SNAP and SNAP effects by ODQ confirms that NO and cGMP mediate the AT(2) receptor inhibition of renal renin production.

DISSOCIATION OF BLOOD PRESSURE AND SYMPATHETIC ACTIVATION OF RENIN RELEASE IN SINOAORTIC-DENERVATED RATS

1. Blood pressure (BP) and heart rate (HR) increase 6 and 24 h after sinoaortic baroreceptor denervation (SAD), whereas plasma renin activity (PRA) and renal renin mRNA levels remain unchanged. We postulated that a simultaneous rise in BP could offset the expected activation of renin associated with an increased renal sympathetic discharge secondary to SAD. 2. To test this hypothesis, the increase in BP associated with the onset of SAD was prevented by a continuous infusion of sodium nitroprusside (SNP; 30 microg/kg per h). Changes were measured in five groups of conscious adult male Wistar rats: (i) sham; (ii) SAD; (iii) SAD rats in which the BP was prevented from increasing by infusion of SNP; (iv) sham rats in which the BP was increased by 30% by infusion of phenylephrine (PE; 1.5-2.0 mL/h); and (v) SNP + PE for 3 h by infusion as above. 3. As expected, BP and heart rate (HR) increased significantly following SAD compared with sham rats (152 +/- 4 vs 116 +/- 3 mmHg, respectively, for BP and 503 +/- 6 vs 345 +/- 13 b.p.m., respectively for HR; n = 5; P < 0.05) but remained unchanged when SNP was infused for 3 h (106 +/- 1 mmHg and 455 +/- 9 b.p.m., respectively; n = 5; P < 0.05). 4. Similarly, BP and HR increased with PE infusion compared with PE + SNP (138 +/- 9.9 vs 113 +/- 2.3 mmHg for BP, respectively, and 325 +/- 9 vs 423 +/- 18 b.p.m. for HR, respectively; n = 5; P < 0.05). 5. Plasma renin activity remained unchanged in SAD compared with sham rats (1.67 +/- 0.35 vs 1.05 +/- 0.17 ng angiotensin (Ang) I/mL per h), but increased significantly when hypertension was prevented (5.86 +/- 0.77 ng AngI/mL per h; n = 5; P < 0.05). Renin mRNA levels in the kidneys were unchanged in all groups. 6. These results show that an elevation in BP appears to offset increased renal sympathetic discharge with no change in PRA.

Renal baroreceptor-stimulated renin in the eNOS knockout mouse

The role of endothelium-derived nitric oxide (NO) in renal baroreceptor stimulation of renin was tested comparing endothelial nitric oxide synthase (eNOS)-deficient mice with C57BL/6J (C57) controls. We measured blood pressure, renal blood flow (RBF), and plasma renin concentration (PRC) in Inactin-anesthetized mice. Blood pressure in eNOS knockout mice was higher than in controls (100 +/- 3 vs. 86 +/- 1 mmHg, respectively; P < 0.001), but RBF was similar (1.71 +/- 0.06 vs. 1.66 +/- 0.09 ml. min(-1). 100 mg kidney wt(-1), respectively), so that renal vascular resistance was also higher in the knockouts (59.81 +/- 2.07 vs. 51.81 +/- 2.66 resistance units, respectively; P < 0.025). PRC was similar (8.24 +/- 1.57 in eNOS knockouts vs. 7.10 +/- 1.19 ng ANG I. ml(-1). h(-1) in C57). NOS inhibition with nitro-L-arginine methyl ester (L-NAME) in C57 controls increased blood pressure (from 85 +/- 2 to 106 +/- 1 mmHg, P < 0.001) and decreased RBF (from 1.66 +/- 0.09 to 1.08 +/- 0.02; P < 0.005), but L-NAME had no effect in eNOS knockout mice. When renal perfusion pressure was reduced in C57 controls to 55 mmHg, PRC increased from 6.6 +/- 0.9 to 14.5 +/- 1.9 microg. ml(-1). h(-1) (P < 0.025), but this response was blocked by L-NAME. However, in eNOS knockouts, reduced renal perfusion pressure increased PRC from 7.6 +/- 1.4 to 15.0 +/- 2.8 microg. ml(-1). h(-1) (P < 0.001). Thus in the chronic absence of eNOS, blood pressure was elevated, but RBF was normal. Additionally, the absence of eNOS did not modify baroreceptor-stimulated renin, suggesting that eNOS-derived NO does not directly mediate this renin-regulating pathway.

Effect of inhibition of nitric oxide synthase on blood pressure and renal sodium handling in renal denervated rats

The role of sympathetic nerve activity in the changes in arterial blood pressure and renal function caused by the chronic administration of N G-nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide (NO) synthesis, was examined in sham and bilaterally renal denervated rats. Several studies have demonstrated that sympathetic nerve activity is elevated acutely after L-NAME administration. To evaluate the role of renal nerve activity in L-NAME-induced hypertension, we compared the blood pressure response in four groups (N = 10 each) of male Wistar-Hannover rats weighing 200 to 250 g: 1) sham-operated vehicle-treated, 2) sham-operated L-NAME-treated, 3) denervated vehicle-treated, and 4) denervated L-NAME-treated rats. After renal denervation or sham surgery, one control week was followed by three weeks of oral administration of L-NAME by gavage. Arterial pressure was measured weekly in conscious rats by a tail-cuff method and renal function tests were performed in individual metabolic cages 0, 7, 14 and 21 days after the beginning of L-NAME administration. L-NAME (60 mg kg-1 day-1) progressively increased arterial pressure from 108 +/- 6.0 to 149 +/- 12 mmHg (P<0.05) in the sham-operated group by the third week of treatment which was accompanied by a fall in creatinine clearance from 336 +/- 18 to 222 +/- 59 microl min-1 100 g body weight-1 (P<0. 05) and a rise in fractional urinary sodium excretion from 0.2 +/- 0. 04 to 1.62 +/- 0.35% (P<0.05) and in sodium post-proximal fractional excretion from 0.54 +/- 0.09 to 4.7 +/- 0.86% (P<0.05). The development of hypertension was significantly delayed and attenuated in denervated L-NAME-treated rats. This was accompanied by a striking additional increase in fractional renal sodium and potassium excretion from 0.2 +/- 0.04 to 4.5 +/- 1.6% and from 0.1 +/- 0.015 to 1.21 +/- 0.37%, respectively, and an enhanced post-proximal sodium excretion compared to the sham-operated group. These differences occurred despite an unchanged creatinine clearance and Na+ filtered load. These results suggest that bilateral renal denervation delayed and attenuated the L-NAME-induced hypertension by promoting an additional decrease in tubule sodium reabsorption in the post-proximal segments of nephrons. Much of the hypertension caused by chronic NO synthesis inhibition is thus dependent on renal nerve activity.

Renal vascular and biochemical responses to systemic renin inhibition in dogs at low renal perfusion pressure

Renin is produced by the kidney and secreted into the systemic circulation. However, its biochemical and physiological role of regulating renal blood flow with changing renal perfusion pressure (RPP) is not fully understood. In this study, the function of the intrarenal renin for production of angiotensin (Ang) I and maintenance of vascular tone was evaluated in dogs under normal conditions and when the kidney was perfused at low RPP. The dog left kidney was perfused first at normal (100 mm Hg) and then at low (30 mm Hg) RPP in the presence or absence of the renin inhibitor ciprokiren (3 mg/kg, i.v.). Both hemodynamic and biochemical parameters were measured. Lowering RPP markedly reduced left renal blood flow and elevated left renal vascular resistance. These effects were prevented by ciprokiren, which blocked the intrarenal production of Ang I. Lowering RPP increased the renal venous/ arterial ratio from 1.4+/-0.1 to 3.6+/-0.3 for plasma renin activity and from 2.4+/-0.2 to 9.8+/-1.1 for Ang I, but did not change the venous/arterial ratio for Ang II. The net renal venous conversion rate of Ang I to Ang II decreased from 0.22 to 0.09 after RPP was lowered, whereas the conversion rate in arterial blood was 1.35 and did not decrease significantly. Our results demonstrated the importance of intrarenal renin-angiotensin system for Ang I production and for the maintenance of the vascular tone, especially at low RPP. Our study also shows the limited capacity for Ang I conversion in the renal vasculature in vivo.

Losartan-sensitive renal damage caused by chronic NOS inhibition does not involve increased renal angiotensin II concentrations

BACKGROUND

Chronic nitric oxide synthase (NOS) inhibition results in hypertension, proteinuria, and renal morphological changes. Continuous angiotensin II (Ang II) blockade prevents these effects, suggesting an essential role of Ang II. However, it is not known whether renal Ang II concentrations are primarily increased or whether the scarcity of NO allows normal concentrations of Ang II to cause these detrimental effects. Therefore, we measured renal Ang II concentrations before and during the development of renal damage.

METHODS

Group 1 served as controls. Groups 2 through 5 received the NOS inhibitor Nomega-nitro-L-arginine (L-NNA; 40 mg/kg/day) for 4, 7, 14, and 21 days, respectively. Systolic blood pressure (SBP), proteinuria, glomerular filtration rate (GFR), and renal and blood Ang II were measured. In a separate experiment, rats were treated with L-NNA + the Ang II AT1 receptor blocker losartan to determine the functional effects of endogenous Ang II during chronic NOS inhibition.

RESULTS

L-NNA treatment resulted in an increase in SBP from day 4 (161 +/- 4 vs. 135 +/- 4 mm Hg in control, P < 0.05) to day 21 (230 +/- 9 mm Hg). GFR was decreased from day 4 (1.9 +/- 0.2 vs. 2.5 +/- 0.2 ml/min in control, P < 0.05) to day 21 (1.2 +/- 0.2 ml/min). Proteinuria was increased from day 14 (85 +/- 14 vs. 6 +/- 1 mg/day in control, P < 0.05) to day 21 (226 +/- 30 mg/day). L-NNA treatment during four days resulted in a significant decrease in renal Ang II (183 +/- 32 vs. 454 +/- 40 fmol/g in control, P < 0.05). On day 7, 14, and 21, renal Ang II was not significantly different from the control. Blood Ang II was not significantly different from the control on days 4, 7, and 14 but was significantly increased after 21 days of L-NNA treatment (215 +/- 35 vs. 78 +/- 13 fmol/ml in control, P < 0.05). Ang II type-1 (AT1) receptor blockade prevented the severe renal injury and hypertension induced by chronic NOS inhibition.

CONCLUSIONS

Losartan-sensitive renal damage caused by chronic NOS inhibition does not involve increased renal Ang II concentrations. This suggests that the detrimental effects of endogenous Ang II are increased during chronic NOS inhibition. Thus, when NO levels are low, normal Ang II concentrations can cause renal injury and hypertension.

Transmural pressure inhibits prorenin processing in juxtaglomerular cell

Pressure control of renin secretion involves a complex integration of shear stress, stretch, and transmural pressure (TP). This study was designed to delineate TP control of renin secretion with minimal influence of shear stress or stretch and to determine its mechanism. Rat juxtaglomerular (JG) cells were applied to a TP-loading apparatus for 12 h. In cells conditioned with atmospheric pressure or atmospheric pressure + 40 mmHg, renin secretion rate (RSR) averaged 29.6 +/- 3.7 and 14.5 +/- 3.3% (P < 0.05, n = 8 cultures), respectively, and active renin content (ARC) averaged 47.3 +/- 4.6 and 38.4 +/- 3.4 ng of ANG I. h(-1). million cells(-1) (P < 0.05, n = 10 cultures), respectively. Total renin content and renin mRNA levels were unaffected by TP. The TP-induced decrease in RSR was prevented by Ca(2+)-free medium and the Ca(2+) channel blocker verapamil and was attenuated by thapsigargin and caffeine, which deplete intracellular Ca(2+) stores. Thapsigargin and caffeine, but not Ca(2+)-free medium or verapamil, prevented TP-induced decreases in ARC. The adenylate cyclase activator forskolin did not modulate TP-induced decreases in RSR or ARC. These findings suggest that TP not only stimulates Ca(2+) influx but also inhibits prorenin processing through an intracellular Ca(2+) store-dependent mechanism and thus inhibits active renin secretion by JG cells.

Role of nitric oxide in the control of renin secretion

Because of the significant constitutive expression of NO synthases in the juxtaglomerular apparatus, nitric oxide (NO) is considered as a likely modulator of renin secretion. In most instances, NO appears as a tonic enhancer of renin secretion, acting via inhibition of cAMP degradation through the action of cGMP. Depending on as yet unknown factors, the stimulatory effect of NO on renin secretion may also switch to an inhibitory one that is compatible with the inhibition of renin secretion by cGMP-dependent protein kinase activity. Whether NO plays a direct regulatory role or a more permissive role in the control of renin secretion remains to be answered.

Control of the renal renin system by local factors

Local factors, such as prostaglandins (PGs), nitric oxide (NO), and endothelins (ETs), produced in the immediate vicinity of juxtaglomerular (JG) cells can exert significant effects on renin secretion and renin gene expression. PGE2, as the main renotubular PG, and PGI2, as the main endothelial prostanoid, both stimulate renin secretion and renin gene expression by activating cAMP formation in JG cells. Although the direct effect of NO on JG cells is less clear, its overall effect in vivo seems to be to stimulate the renin system. Evidence is emerging that stimulation by NO is related to the cAMP pathway, and cGMP-induced inhibition of cAMP-phosphodiesterase III (PDE-III) may mediate this effect. ETs, on the other hand, appear to inhibit the renin system, in particular in those pathways activated by cAMP, acting via Ca2+- and protein kinase C-related mechanisms. There is increasing evidence that both NO and PGs could be involved in the physiological regulatory mechanisms by which salt intake affects the renin system.

Regulation of renal renin release

Renal renin release is affected by several systemic and intrarenal factors. Systemic factors include sympathetic nerves, circulating angiotensin II, blood pressure and salt balance of the organism. Intrarenal factors involved are nitric oxide and the prostaglandins, which stimulate renin secretion.

Stimulation of renin secretion by nitric oxide is mediated by phosphodiesterase 3

This study aimed to characterize the cellular pathways along which nitric oxide (NO) stimulates renin secretion from the kidney. Using the isolated perfused rat kidney model we found that renin secretion stimulated 4- to 8-fold by low perfusion pressure (40 mmHg), by macula densa inhibition (100 micromol/liter of bumetanide), and by adenylate cyclase activation (3 nmol/liter of isoproterenol) was markedly attenuated by the NO synthase inhibitor nitro-L-arginine methyl ester (L-Name) (1 mM) and that the inhibition by L-Name was compensated by the NO-donor sodium nitroprusside (SNP) (10 micromol/liter). Similarly, inhibition of cAMP degradation by blockade of phosphodiesterase 1 (PDE-1) (20 micromol/liter of 8-methoxymethyl-1-methyl-3-(2-methylpropyl)xanthine) or of PDE-4 (20 micromol/liter of rolipram) caused a 3- to 4-fold stimulation of renin secretion that was attenuated by L-Name and that was even overcompensated by sodium nitroprusside. Inhibition of PDE-3 by 20 micromol/liter of milrinone or by 200 nmol/liter of trequinsin caused a 5- to 6-fold stimulation of renin secretion that was slightly enhanced by NO synthase inhibition and moderately attenuated by NO donation. Because PDE-3 is a cGMP-inhibited cAMP-PDE the role of endogenous cGMP for the effects of NO was examined by the use of the specific guanylate cyclase inhibitor 1-H-(1,2,4)oxodiazolo(4,3a)quinoxalin-1-one (20 micromol). In the presence of 1H-[1,2,4]oxodiazolo[4,3-a]quinoxalin-1-one the effect of NO on renin secretion was abolished, whereas PDE-3 inhibitors exerted their normal effects. These findings suggest that PDE-3 plays a major role for the cAMP control of renin secretion. Our findings are compatible with the idea that the stimulatory effects of endogenous and exogenous NO on renin secretion are mediated by a cGMP-induced inhibition of cAMP degradation.

Stimulation of renin secretion by NO donors is related to the cAMP pathway

This study aimed to characterize the cellular pathways along which nitric oxide (NO) influences the secretion of renin from the kidney. Using the isolated perfused rat kidney model, we found that the NO donor sodium nitroprusside (SNP) (1-30 mumol/l) induced a prompt, concentration-dependent fourfold increase of basal renin secretion. The membrane-permeable cGMP analogs 8-bromo-cGMP and 8-(4-chlorophenylthio)-cGMP (8-pCPT-cGMP; each 5-50 mumol/l) inhibited basal renin secretion and attenuated the stimulation of renin secretion by SNP. Conversely, the renin stimulatory effect of SNP was enhanced in the presence of the G kinase inhibitor Rp-8-CPT-cGMPS (10 mumol/l). The renin stimulatory effect of SNP was amplified in nominally calcium-free perfusate and was abolished in the presence of angiotensin II (1 nmol/l). Renin secretion stimulated by SNP was clearly attenuated by the A kinase inhibitor Rp-8-CPT-cAMPS (25 mumol/l). These findings indicate that the renin stimulatory effect of NO donors in renal juxtaglomerular cells cannot be explained by activation of G kinase and is also less likely to be causally related to the regulation of renin secretion by calcium. Because A kinase activity is required for the stimulation of renin secretion by SNP, it appears as if the renin stimulatory effect is causally related to the cAMP pathway controlling renin secretion.