Is the renin-angiotensin system involved in urinary concentration mechanisms?

Renin release elicited by i.v. injection of loop-diuretics was used to study the effects of angiotensin II (AII) on intrarenal hemodynamics. The vasoconstrictive action of intrarenally synthesized AII predominates in the efferent glomerular arteriole. Such a vasoconstrictive effect could affect blood flow in the vasa recta which stem from efferent arterioles of juxtamedullary glomeruli. Renin secretion and renal inner medullary blood flow (tissue clearance of 133Xe) were simultaneously measured before and after frusemide-induced renin release. The relationship between renin secretion and renal inner medullary blood flow was inverse. Changes in renal medullary blood flow may be physiological determinants of medullary osmolality and renal concentration ability. The intrarenal role of AII in urinary concentration recovery after frusemide was examined. Inhibition of renin release by propranolol or AII-blockade (by saralasin or Hoe 409) delayed recovery of urinary osmolality. In the conscious rat, propranolol slowed down recovery of the cortico-papillary gradient for sodium. Its vasoconstrictive action on the efferent glomerular arteriole might enable the renin-angiotensin system to participate in the control of renal excretion of salt and water.     

Effect on renal function and renin secretion of noradrenaline infused into the renal artery.

Effect of noradrenaline on renal function and renin secretion was studied during infusion into the renal artery of anaesthetized dogs. Experiments were performed with or without alpha or beta receptor blockade. Noradrenaline infusion resulted in a significant elevation of renin secretion associated with marked vasoconstriction. Urine flow rate, the filtered and excreted amounts of sodium were diminished due to the decreased GFR. Alpha receptor blockade suppressed renin secretion in the presence of changes in renal haemodynamics. The simultaneous infusion of noradrenaline enhanced renin release without affecting renal haemodynamics or reducing Na-excretion. Following simultaneous inhibition of alpha and beta receptors renin secretion dropped markedly; there were no further changes in either renin secretion or renal haemodynamics upon the simultaneous administration of noradrenaline. Based on the present findings it is suggested that renin secretion is controlled by both alpha and beta receptors. Beta receptor simulation exerts a direct action, whereas alpha stimulation appears to be mediated in part by indirect mechanisms such as renal haemodynamics.     

Effect of indomethacin and propranolol on the blood pressure and renin response to atriopeptin III in conscious rats

The effect of prostaglandin synthesis inhibition and of beta-adrenoceptor blockade on the blood pressure and renin response to the synthetic atrial natriuretic peptide atriopeptin III was assessed in unanesthetized normotensive rats. This peptide was infused i.v. for 30 min at a rate of 1 microgram/min in rats pretreated either with indomethacin (5 mg i.v.) or propranolol (1 mg i.v.). The blood pressure reducing effect of atriopeptin III was attenuated neither by indomethacin nor by propranolol. Atriopeptin III per se did not modify plasma renin activity. Both the administration of indomethacin and of propranolol had a suppressing effect on renin release during atriopeptin III infusion. These data suggest that the vasodilating properties of atrial natriuretic peptides do not depend in the conscious normotensive rats on the production of prostaglandins. They also provide evidence that during infusion of such peptides, both prostaglandins and beta-adrenergic mechanisms are still involved in the regulation of renin secretion.     

Beta 2-adrenergic stimulation of androgen production by cultured mouse testicular interstitial cells

The present studies characterized the beta-receptor subtype involved in androgen production by cultured mouse testicular interstitial cells and explored the possible stimulation of androgen release by alpha-adrenergic agonists. During a 3-hour incubation period, LH and a non-specific beta-adrenergic agonist, L-isoproterenol steadily increased androgen production with a similar time-course. Isoproterenol, epinephrine, norepinephrine and a specific beta 2-receptor agonist, salbutamol stimulated androgen release in a concentration-dependent manner. The concentrations of the agonists required for half-maximum stimulation (EC50) were approximately 1 nM (isoproterenol), 8 nM (epinephrine), 9 nM (salbutamol) and 2 microM (norepinephrine) giving an order of potency of isoproterenol greater than epinephrine = salbutamol much greater than norepinephrine. L- but not the D-isomer of isoproterenol induced androgen production. A non-selective beta-receptor antagonist, propranolol, abolished androgen production induced by isoproterenol. A selective beta 2-receptor antagonist ICI 118,551 inhibited the isoproterenol effect in a concentration-dependent manner with half-maximum inhibition (IC50) at approximately 23 nM. The beta 1-receptor antagonists, metoprolol and atenolol had no effect on isoproterenol-induced androgen release. The stimulatory effect of norepinephrine (an alpha- and beta-agonist) was completely (100%) abolished by propranolol, unaffected by the alpha-antagonist phentolamine and only partially (35%) inhibited by phenoxybenzamine. Phenoxybenzamine and the alpha 2-agonist, clonidine reduced basal androgen production. These studies indicate that androgen production by primary cultures of mouse testicular interstitial cells occurs exclusively via the beta 2-receptor subtype and that alpha-receptor agonists do not stimulate androgen release by these cells.     

Effects of Bay K 8644 on renal function and renin secretion in anesthetized rats

Our previous study on kidney cortical slices showed that Bay K 8644, a dihydropyridine calcium channel agonist, produced a dose-dependent inhibitory action on the release of renin. The present study was performed to examine the effect of Bay K 8644 on renal function and renin secretion in vivo. When Bay K 8644 was directly infused into the renal artery of anesthetized rats, 2 micrograms/kg/min had no effect on renal blood flow (RBF) and glomerular filtration rate (GFR), but decreased urine flow (UF), urinary sodium excretion (UNaV) and fractional sodium excretion (FENa) by about 30%, 55% and 35%, respectively, thereby suggesting that Bay K 8644 enhanced the tubular reabsorption of water and sodium. When 10 micrograms/kg/min were infused, RBF, GFR, UF, UNaV and FENa decreased to about 95%, 70%, 35%, 35% and 30% of each control value. The administration of Bay K 8644 at 10 micrograms/kg/min did not influence the basal levels of plasma renin activity (PRA) and renin secretion rate (RSR), but did inhibit significantly isoproterenol-induced increasing effects on PRA and RSR. These results indicate that the activation of voltage-dependent calcium channels with Bay K 8644 influences the control of renal function and renin secretion in vivo.     

Pharmacological evidence for involvement of the sympathetic nervous system in the increase in renin secretion produced by a low sodium diet in rats

To determine the degree to which increased sympathetic activity contributes to the increase in renin secretion produced by a low sodium diet, the beta-adrenergic blocking drug propranolol or saline vehicle was injected through indwelling jugular cannulas in rats fed a normal diet and rats fed a low sodium diet for 9 days. Plasma renin activity (PRA) and plasma renin concentration (PRC) were elevated by the low sodium diet, and these values were reduced 42-45% by propranolol, although they were still higher than in the normal diet controls. Plasma corticosterone was moderately elevated in cannulated rats on regular diet, compared to decapitated controls, but corticosterone did not differ between cannulated and decapitated rats on low salt diet; propranolol reduced plasma corticosterone. However, PRA and PRC were comparable in cannulated rats and decapitated controls on both the normal and the low sodium diets, and propranolol did not produce a significant reduction in PRA and PRC in rats fed the normal diet. This indicates that the effects of propranolol on PRA and PRC in the low sodium rats were not simply due to reduction of a stress-induced increase in renin secretion. The results indicate that increased sympathetic activity makes a substantial contribution to the increase in renin secretion produced by 9 days of dietary sodium restriction.     

Blockade of renin or angiotensin for understanding human hypertension: a comparison of propranolol, saralasin and converting enzyme blockade.

To understand the role of the renin-angiotensin-aldosterone system in the pathogenesis of human hypertension, in serial studies we have blocked the system using three different pharmacologic probes: 1) reduction of renin secretion by administration of the beta receptor blocker, propranolol; 2) blockade of the action of angiotensin II by infusion of saralasin, a competitive antagonist of angiotensin II; and 3) blockade of the enzymatic conversion of angiotensin I to angiotensin II by infusing a nonapeptide competitive inhibitor. The depressor responses induced by either propranolol or the nonapeptide expose a significant to major involvement of excess renin--angiotensin in maintaining the hypertension of some 50 to 70% of common forms of hypertension including "essential" hypertension. This subgroup includes nearly all patients with high or "normal" renin--sodium profiles. The considerably lower estimates for a renin factor in essential hypertension suggested by saralasin testing now appear due to the partial agonism of this drug. Further studies are required to determine whether this relative or absolute excess of renin secretion is primarily involved in the hypertension and if not why it fails to shut itself off. Similar studies of normal subjects are also needed to determine whether renin support of blood pressure is proportionately greater or less than in hypertensive subjects. Meanwhile the validation provided by these three different pharmacologic probes portends a burgeoning clinical role for renin--sodium profiling not only in screening for renal and adrenal cortical hypertensions but also for characterizing the vasoconstrictor and volume elements involved in various individual patients and thus enabling more specific treatments of the various subtypes of essential hypertension.     

Beta-adrenoceptors and the regulation of blood pressure and plasma renin during exercise

The relative role of beta 1- and beta 2-adrenoceptors in the regulation of blood pressure and plasma renin at rest and during exercise was studied in 17 normal male volunteers. They performed, in a randomized order and according to a double-blind crossover study design, three graded and uninterrupted exercise tests until exhaustion after being pretreated during 3 consecutive days with a placebo, with a predominantly beta 1-blocker (atenolol, 50 mg once/day), or with a predominantly beta 2-blocker (ICI 118551, 20 mg 3 times/day). Both drugs caused a decrease of heart rate, but the reduction by ICI 118551 was less pronounced at rest and no additional decline occurred at exercise. ICI 118551 did not affect blood pressure at rest, but during exercise diastolic blood pressure was higher than after a placebo. Atenolol lowered systolic blood pressure at rest and suppressed the exercise-induced increase in systolic blood pressure. At rest and during exercise plasma renin activity was lowered by predominantly beta 1-blockade and unchanged during beta 2-antagonism. The exercise-induced increase in plasma renin was, however, not affected by the beta 1-blocker. After atenolol the urinary excretion of aldosterone was decreased but the plasma aldosterone concentration was not changed. ICI 118551 did not alter plasma or urinary aldosterone. Our results therefore provide further evidence that the adrenoceptors mediating the release of renin at rest and during exercise in humans are partially of the beta 1-subtype, whereas beta 2-adrenergic receptors probably play only a minor role in the control of renin secretion, especially at exercise.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of prostaglandin E1 on renin and aldosterone in hypertensive patients.

The effect of prostaglandin E1 (PGE1) on plasma renin activity (PRA) and plasma aldosterone concentration (PAC) was studied in the hypertensive subjects treated with or without 75 mg indomethacin or 60 mg propranolol for a week. Subsequent to the treatment with indomethacin for a week, PRA and PAC levels were decreased as compared to the control, without changes in the blood pressure and heart rate. During the infusion of PGE1, the blood pressure was decreased and the pulse rate was increased. PRA and PAC levels were also elevated. These changes of parameters were not different between the control and the indomethacin-treated subjects. PRA and PAC were suppressed after the treatment with propranolol. With the infusion of PGE1, the level of PRA was not significantly elevated, while, PAC was significantly increased by the infusion of 100 ng/Kg/min of PGE1. During the infusion of PGE1, the blood pressure was decreased while the pulse rate was increased in the subjects treated with propranolol. However, the elevation of the pulse rate was less remarkable than the control. These data indicate that PGE1 have important roles in the regulation of the release of renin and aldosterone. These findings also suggest that PGE1 may act to stimulate the secretion of aldosterone in man.     

β2-肾上腺素受体在新生大鼠心肌成纤维细胞中的分布及其促增殖作用

为了明确β-肾上腺素受体(AR)亚型在新生大鼠心肌成纤维细胞中的分布及其在成纤维细胞增殖反应中的作用,采用放射配体结合实验和[3H]-thymidine掺人法检测了新生大鼠心肌成纤维细胞的β-AR密度和DNA合成速率。结果显示,在培养心肌细胞和心肌成纤维细胞中β-AR密度(Bmtax)和解离常数(Kp)无显著性差异;竞争抑制曲线分析结果提示,心肌成纤维细胞对CGP 20712A和ICI ll8551单位点拟合均显著优于两位点拟合(P＜0．01),表现为对选择性β1-AR拮抗剂CGP 20712A的低亲和性(IC50值：10．1μmol/L)和对选择性β2-AR拮抗剂ICI 118551的高亲和性(IC50值：0.147μmol/L)。异丙肾上腺素(ISO)促心肌成纤维细胞增殖作用可被ICI 118551和心得安(非选择性β-AR拮抗剂)完全抑制,而CGP20812A则无此作用。上述结果提示,在培养心肌成纤维细胞中β-AR亚型占绝对优势,并且ISO引起的心肌成纤维细胞增殖反应是由β2-AR介导的。     

电刺激兔下丘脑乳头体核上区及内侧视前区对血浆肾素活性的影响

本工作观察了电刺激麻醉兔的乳头体核上区及内侧视前区对血浆肾素活性(Plasmarenin activity,PRA)的影响。电刺激乳头体核上区引起血压升高、心率减慢、呼吸变快变浅、PRA增加120％,双侧去肾神经后或静脉注射心得安后,同样的刺激使PRA增加的现象基本消失。电刺激内侧视前区导致血压下降、心率加快、呼吸加深、PRA降低30.7％,双侧去肾神经后,电刺激内侧视前区使PRA降低的作用明显减弱。上述两组实验表明,电刺激兔下丘脑乳头体核上区及内侧视前区可分别增加或减少肾素释放。     

Isoproterenol-induced desensitization of mucin release in isolated rat submandibular acini

Release of [14C]glucosamine-labelled mucins was studied in vitro using well-characterised preparations of rat submandibular acini. Mucin release was stimulated by forskolin, an activator of the catalytic subunit of adenylate cyclase, and 3-isobutyl-1-methylxanthine (IBMX), a cyclic nucleotide phosphodiesterase inhibitor. Both stimulated in a dose-dependent manner to the same maximum as that seen with isoproterenol. Neither forskolin nor IBMX added in the presence of isoproterenol increased secretion above the maximum in response to isoproterenol alone, suggesting a similar mechanism of action, mediated by cyclic AMP. Prior exposure of acini to isoproterenol (10 microM) for 45 min, followed by washout resulted in (a) persistent increase in basal secretion which was abolished by propranolol and (b) reduced stimulation of mucin secretion in response to either a second isoproterenol challenge, noradrenaline or forskolin. Thus, exposure of rat submandibular acini in vitro desensitizes the cells to subsequent stimulation. Although this mimics the decreased beta-adrenergic secretory responses seen in submandibular cells from cystic fibrosis patients, results suggest that the isoproterenol-induced desensitization is at the level of beta-receptor and adenylate cyclase, rather than distal to cyclic AMP.     

The role of beta receptors in the regulation of renin release.

The effect of the primarily beta 2 type adrenergic receptor stimulating terbutaline (10(-7)--10(-5) M) and of the beta 1 and beta 2 type adrenergic receptor stimulating isoproterenol (10(-7)--10(-5) M) was studied on renin release from incubated slices of renal cortex. Renin release and cAMP content of the slices were significantly higher in the presence of both terbutaline and isoproterenol. A logarithmic dose--response relationship was shown to be present between the beta mimetics and the renin concentration in the medium, and the cAMP content of tissue slices. In equal doses isoproterenol was about 1.5 times more potent than terbutaline. No change was seen in the renin content of the tissue slices. The results supports the view that beside the beta 1 type adrenergic receptors of the renal cortex--even if to a lesser extent--the beta 2 type adrenergic receptors, too, are involved in the regulation of renin release.     

Effect of DuP 753, a nonpeptide angiotensin II receptor antagonist, on the drinking responses to acutely administered dipsogenic agents in rats.

The present studies examine the effect of the nonpeptide angiotensin II (AII) type 1 receptor antagonist, DuP 753, on water intake in rats treated with dipsogenic stimuli, which are thought to induce drinking via release of renin and subsequent formation of AII. Subcutaneous administration of DuP 753 in doses that are known to inhibit drinking induced by AII failed to inhibit the water intake of rats following subcutaneous administration of the beta-adrenoceptor agonist isoproterenol. The peptide antagonist1 Sar, 8Ileu-AII, which blocks both AII type 1 and AII type 2 receptors, also failed to inhibit isoproterenol-induced drinking, suggesting that neither subtype is involved in this drinking response. Additional studies verified previous reports that acute subcutaneous administration of both the beta-adrenoceptor antagonist propranolol and the angiotensin I-converting enzyme inhibitor captopril could block the drinking response to subcutaneous administration of isoproterenol. Subcutaneous administration of DuP 753 also failed to inhibit the drinking responses to subcutaneous administration of serotonin, 5-hydroxytryptophan, hypertonic saline, and polyethylene glycol. However, central intraventricular administration of DuP 753 inhibited the drinking response to subcutaneous administration of isoproterenol. The results are discussed in terms of the importance of AII in mediating isoproterenol-, serotonin-, and 5-hydroxytryptophan-induced water intake and suggest a need to readdress this mechanism.     

Mechanisms of leptin secretion from white adipocytes

The mechanisms regulating leptin secretion were investigated in isolated rat white adipocytes. Insulin (1-100 nM) linearly stimulated leptin secretion from incubated adipocytes for at least 2 h. The adrenergic agonists norepinephrine, isoproterenol (two nonselective beta-agonists), or CL-316243 (potent beta3) all inhibited insulin (10 nM)-stimulated leptin release. The inhibitory effects of norepinephrine and isoproterenol could be reversed not only by the nonselective antagonist propranolol but also by the selective antagonists ICI-89406 (beta1) or ICI-118551 (beta2), the beta2-antagonist being less effective than the beta1. Insulin-stimulated leptin secretion could also be inhibited by a series of agents increasing intracellular cAMP levels, such as lipolytic hormones (ACTH and thyrotropin-stimulating hormone), various nonhydrolyzable cAMP analogs, pertussis toxin, forskolin, methylxanthines (caffeine, theophylline, IBMX), and specific inhibitors of phosphodiesterase III (imazodan, milrinone, and amrinone). Significantly, antilipolytic agents other than insulin (adenosine, nicotinic acid, acipimox, and orthovanadate) did not mimic the acute stimulatory effects of insulin on leptin secretion under these conditions. We conclude that norepinephrine specifically inhibits insulin-stimulated leptin secretion not only via the low-affinity beta3-adrenoceptors but also via the high-affinity beta1/beta2-adrenoceptors. Moreover, it is suggested that 1) activation of phosphodiesterase III by insulin represents an important metabolic step in stimulation of leptin secretion, and 2) lipolytic hormones competitively counterregulate the stimulatory effects of insulin by activating the adenylate cyclase system.     

Multiple defects in the renin-angiotensin system in alloxan-diabetic kidney

A defect in the renin-angiotensin system has been shown in diabetic patients and experimental animals, in particular with nephropathy or autonomic neuropathy. The mechanism for this low plasma renin activity (PRA) is poorly understood. In order to clarify this defect, the renin-angiotensin system was studied in alloxan-induced diabetic and age-match control mice. In diabetic animals, kidney renin activity (KRA) was significantly lower than that of the controls, while plasma renin substrate (PRS) concentration was slightly higher and PRA was normal. The amount of injected radiolabeled renin extracted by the kidney was normal, but the amount extracted by the liver was significantly decreased in diabetic animals. On the other hand, the degradation of the extracted renin by both the kidney and the liver was elevated as compared to the controls. This high degradation rate was accompanied by a slight increase in lysosomal protease activity in the kidneys. In in vivo studies, isoproterenol-induced PRA was 20-fold in control animals. In diabetics, isoproterenol-induced PRA was attenuated and rose only four- to fivefold over basal level. The angiotensin converting enzyme (ACE) activity in the kidney was significantly decreased in the diabetic state. It is concluded that there were multiple defects in the renin-angiotensin system in this diabetic model, namely, a depletion of renin storage with subsequent loss of maximal responsiveness to the adrenergic agonist in renin release, an elevation of intrarenal renin degradation together with a deficiency in ACE which would possibly lead to a decrease in intrarenal formation of angiotensin II.     

Decreased renin release and constant kallikrein secretion after injection of L-NAME in isolated perfused rat kidney.

A possible role of the endothelial L-arginine/NO pathway in the control of renal hemodynamics, renin release and kallikrein secretion was studied in an isolated rat kidney model perfused in a closed-circuit. NG-nitro-L-arginine methyl ester (L-NAME, 1-50 microM), an inhibitor of nitric oxide biosynthesis, caused a dose-dependent increase in perfusion pressure (PP) and a dose-dependent decrease in renal perfusate flow. Renin release was inhibited independently of a rise in PP. L-NAME did not change the urinary kallikrein secretion. These results confirm the intervention of the L-arginine/NO pathway in the vasodilation of this isolated perfused kidney model and demonstrate the inhibitory effect of L-NAME on renin release. They suggest that nitric oxide synthesis plays a role in stimulating renin release and is not involved in the regulation of urinary kallikrein secretion.     

Cyclosporine A inhibits prostaglandin E2 release, and has no effect on renin secretion, from rat renal cortical slices

These experiments were designed to test the hypothesis that cyclosporine A (CSA) inhibits renin secretion and stimulates renal prostaglandin E2 (PGE2) release in vitro. In rat renal cortical slices incubated at 37 degrees C in a buffered and oxygenated physiological saline solution containing 4 mM KCl, CSA concentrations ranging from 1 to 30 microM had no significant effect on renin secretion. Furthermore, partial depolarization of the cells, produced by increasing extracellular KCl concentration to 20 mM, failed to reveal any latent inhibitory or stimulatory effects of CSA on renin secretion. On the other hand, PGE2 release was significantly inhibited by CSA over the same range of concentrations. This inhibitory effect might be explained by the previous findings of others, that CSA inhibits phospholipase A2 activity, thereby decreasing arachidonic acid production, the rate-limiting step in PG synthesis. In conclusion, CSA inhibits PGE2 release but fails to affect renin secretion in vitro. These results suggest that the occasional effects of CSA on renin secretion in intact animals must be attributable to indirect and/or chronic effects.     

A targeting sequence for dense secretory granules resides in the active renin protein moiety of human preprorenin

Human renin plays an important role in blood pressure homeostasis and is secreted in a regulated manner from the juxtaglomerular apparatus of the kidney in response to various physiological stimuli. Many aspects of the regulated release of renin (including accurate processing of prorenin to renin, subcellular targeting of renin to dense secretory granules, and regulated release of active renin) can be reproduced in mouse pituitary AtT-20 cells transfected with a human preprorenin expression vector. Using protein engineering, we have attempted to define the roles of various structures in prorenin that affect its production and trafficking to dense core secretory granules, resulting in its activation and regulated secretion. Replacement of the native signal peptide of human preprorenin with that of a constitutively secreted protein (immunoglobulin M) had no apparent effect on either the constitutive secretion of prorenin or the regulated secretion of active renin in transfected AtT-20 cells. Removal of the pro segment resulted in a marked reduction in total renin secretion, but did not prevent renin from entering the regulated secretory pathway. Single or combined mutations in the two glycosylation sites of human renin did not prevent its regulated secretion; however, the complete elimination of glycosylation resulted in a significant increase in the ratio of renin/prorenin secreted by the transfected cells. Thus, these results suggest that 1) at least one of the sequences that target human renin to dense secretory granules lies within the protein moiety of active renin; 2) the presence of the pro segment is important for efficient prorenin and renin production; and 3) glycosylation can quantitatively affect the proportion of active renin secreted.     

Renin release in anesthetized rats is enhanced by the calmodulin antagonist W-7

In foregoing work, we found that the release of renin from rat kidney cortical slices was stimulated by the calmodulin antagonist W-7. The present work was done to determine whether W-7 would stimulate renin release in vivo. W-7 and its control agent, W-5 were directly infused into the renal artery of anesthetized rats. W-7 and W-5, at 50 micrograms/kg/min, produced no significant effects on renin release. Infusion of W-7 at 100 micrograms/kg/min resulted in a marked stimulation of renin release, but there was no significant alteration in the release when the same dose of W-5 was infused. Both compounds elicited a slight decrease in renal blood flow. The alterations in renin release and renal blood flow seen with W-7 were not affected by pretreatment with phentolamine or propranolol. As W-7 stimulates renin release in vivo, the hypothesis that Ca2+-calmodulin plays an inhibitory role in renin release from the kidney is given added support.