Renin release: relation to renal sodium load and dissociation from hemodynamic changes

Tubular control of renin synthesis and secretion

The intratubular composition of fluid at the tubulovascular contact site of the juxtaglomerular apparatus serves as regulatory input for secretion and synthesis of renin. Experimental evidence, mostly from in vitro perfused preparations, indicates an inverse relation between luminal NaCl concentration and renin secretion. The cellular transduction mechanism is initiated by concentration-dependent NaCl uptake through the Na-K-2Cl cotransporter (NKCC2) with activation of NKCC2 causing inhibition and deactivation of NKCC2 causing stimulation of renin release. Changes in NKCC2 activity are coupled to alterations in the generation of paracrine factors that interact with granular cells. Among these factors, generation of PGE2 in a COX-2-dependent fashion appears to play a dominant role in the stimulatory arm of tubular control of renin release. [NaCl] is a determinant of local PG release over an appropriate concentration range, and blockade of COX-2 activity interferes with the NaCl dependency of renin secretion. The complex array of local paracrine controls also includes nNOS-mediated synthesis of nitric oxide, with NO playing the role of a modifier of the intracellular signaling pathway. A role of adenosine may be particularly important when [NaCl] is increased, and at least some of the available evidence is consistent with an important suppressive effect of adenosine at higher salt concentrations.

Cerebral osmoregulatory reduction of plasma renin concentration in sheep

A centrally mediated inhibitory influence of plasma hypertonicity on renin secretion was investigated in conscious, Na-depleted sheep. Infusions of hypertonic solutions were made into the carotid artery or jugular vein, and the effects on plasma renin concentration (PRC) compared. Intracarotid infusion of 1.65 M NaCl significantly reduced PRC (to 74% of the pre-infusion value) within 15 min of the commencement of the infusion whereas corresponding intrajugular infusion did not. Intracarotid infusion of 3 M sorbitol for 45 min also reduced PRC (to 64% of the pre-infusion level) significantly after 15 min of infusion. By contrast, neither intrajugular infusion of 3 M sorbitol, nor intracarotid infusion of isotonic 0.15 M NaCl for 45 min significantly reduced PRC. Intracarotid infusion of hypertonic sorbitol for 45 min did not inhibit PRC in sheep with cerebral lesions of the lamina terminalis. These results show that plasma hypertonicity may have an inhibitory influence on renin secretion. The inhibition is probably mediated by an effect of hypertonicity on the CNS, rather than a direct effect on the kidney.

Stimulation of renin secretion by non-diuretic sulfhydryl reagents

Organomercurial diuretics stimulate renin secretion although the underlying cellular mechanisms remain undefined. Since organomercurials are also known to react with sulfhydryl groups, the present studies determined the effects of sulfhydryl reagents on renin secretion. The effects of the non-diuretic mercurial agent, parachloromercuriphenyl-sulfonate (PCMPS), as well as that of other sulfhydryl reagents, N-ethylmaleimide (NEM), N-phenylmaleimide (NPM) and monobromotrimethylammoniobimane (qBBR), on renin secretion were determined in rabbit renal cortical slices. All four reagents stimulated renin secretion. NEM, which has a high membrane permeability, stimulated secretion to a relatively small extent and its effects were not apparent for at least one hour. Conversely, PCMPS, which is much less permanent than NEM, produced the largest stimulation and these effects were apparent within one hour. The stimulation of secretion by sulfhydryl reagents was independent of the concentration of Ca2+, Na+, and K+ in the incubation media, suggesting that the stimulation is not secondary to alterations of intracellular ion concentrations. These results raise the possibility of direct involvement of sulfhydryl groups of particular membrane protein(s) of the juxtaglomerular (JG) cells in some steps leading to renin secretion, and raise the possibility that sulfhydryl reactivity might in part account for the stimulatory effects of organomercurial and other diuretics.

Acute effect of Russell's viper (Vipera russelli siamensis) venom on renal hemodynamics and autoregulation of blood flow in dogs

Renal hemodynamics and autoregulation of blood flow were investigated following intravenous injection of Russell's viper venom (0.1 mg/kg) in dogs anesthetized with sodium pentobarbital. After venom injection, the glomerular filtration rate fell significantly throughout the experimental period of three hr. Urine flow rate and renal blood flow also decreased and the filtered load of electrolytes declined significantly. The fractional excretion of sodium, potassium and phosphorus increased following venom administration. These data suggest that the venom may depress both glomerular and tubular functions. The renal autoregulation of blood flow was maintained during the experimental reduction of renal arterial pressure. We conclude that the ability of renal vasculature to autoregulate renal blood flow is not inhibited by Russell's viper venom, even though renal function is depressed.

Dissociation of the responses of the renin-angiotensin system and sympathetic nervous system to a vasodilator stimulus in congestive heart failure

The ability of neurohumoral reflex control mechanisms to respond to a vasodilator mediated alteration in hemodynamic status was studied. A sodium nitroprusside infusion was administered to 5 normal subjects and 47 patients with severe congestive heart failure resulting in significant decreases in mean arterial pressure and in systemic vascular resistance. As expected in normals the vasodilator stimulus caused a reflex activation in both the renin-angiotensin system and sympathetic nervous system as measured by increased plasma renin activity and plasma norepinephrine, respectively. In the patients with heart failure, plasma renin activity rose similarly in response to nitroprusside (+63% in heart failure, 100% in normals, P = NS) while plasma norepinephrine remained essentially unchanged (+11% in heart failure, 98% in normals, P less than 0.01). These data demonstrate that the neurohumoral dysfunction seen in patients with heart failure is not uniform. In patients with severe congestive heart failure the renin-angiotensin system apparently is activated by mechanisms other than sympathetic nervous stimulation. This intact reflex humoral response may still function in opposition to the beneficial hemodynamic effects produced by direct vasodilators such as nitroprusside.

Effects of adenosine on renin release from isolated rat glomeruli and kidney slices

Adenosine produced by the macula densa cells in response to changes in the tubular NaCl-concentration has been suggested to inhibit renin release in vivo. In order to test this suggestion we studied: incubated kidney cortical slices (KS) which contain both the macula densa and the entire afferent arteriole; superfused single microdissected glomeruli (LAG) without macula densa but with the afferent arteriole preserved; and superfused batches of selected glomeruli (SAG) containing only the juxtaglomerular cells closest to the glomerulus. For superfusion and incubation a bicarbonate Ringer solution was used. The specificity of the renin release process was validated by measuring adenylate kinase as a marker for cytoplasmatic leak. Adenosine (10 micrograms/ml) halved basal renin release from incubated KS as compared to controls (P less than 0.001, n = 8, 8). Renin release from LAG stimulated by calcium depletion was also inhibited (P less than 0.05, n = 8, 9) whereas basal release was not affected (n = 6, 12). No effect was detected neither on basal nor on calcium stimulated renin release from SAG. We conclude that adenosine inhibits renin release in vitro by a mechanism independent of a functioning nephron, and which involves only the JG-cells located in the afferent arteriole at some distance from the glomerulus.

Renal function impairment induced by change in posture in patients with cirrhosis and ascites

The assumption of upright posture by patients with liver cirrhosis leads to striking activation of adrenergic and renin-angiotensin systems. The tilting-induced modifications in renal function of eight healthy controls and 14 untreated patients with liver cirrhosis and ascites were related to plasma concentrations of noradrenaline, renin activity and aldosterone. All patients had preserved renal blood perfusion. All parameters were evaluated during bed rest for two hours and in the sitting posture for one hour. Basal plasma renin activity (0.1 greater than p greater than 0.05), aldosterone and noradrenaline concentrations (p less than or equal to 0.01) were raised in cirrhotics. The renal function tests (creatinine clearance, filtered sodium, tubular rejection fraction, urinary sodium excretion) were significantly reduced in cirrhosis. Under basal conditions, in cirrhotic patients tubular rejection fraction and urinary sodium excretion were inversely related to both noradrenaline and aldosterone concentrations. After tilting, the noradrenaline and aldosterone integrated outputs (sigma delta) were significantly greater in cirrhosis. All renal function tests significantly decreased in cirrhotics, whereas creatinine clearance only significantly decreased in controls. Patient's tubular rejection fraction of sodium and sodium excretion were related to sigma delta aldosteronaemia (r = -0.72; p less than 0.01), but no longer to sigma delta plasma noradrenaline.

Effect of sustained hypernatraemia on the renin-aldosterone system in the dog

1. To determine if increases in plasma sodium concentration P[Na] have any sustained effects of the renin-aldosterone system, P[Na] was increased in a group of six dogs over a period of 6 days by increasing sodium intake from 10 to 200 mmol per day while a fixed 700 ml per day water intake was maintained along with a continuous i.v. infusion of antidiuretic hormone (ADH) at a rate of 2.4 units per day. 2. P[Na] rose from 137.3 +/- 2.0 to 153.6 +/- 6.5 mmol/l during the high intake period. Plasma potassium concentration, 22Na space, and mean arterial pressure all remained near control levels in response to Na loading. 3. Plasma renin activity (PRA) averaged 1.0 +/- 0.1 ngAI/ml per hour on the final low Na day and fell transiently to 0.6 +/- 0.2 ngAI/ml per hour on the first day of sodium loading. For the duration of the study it remained at the control level. Plasma aldosterone concentration fell from the low Na level of 15.4 +/- 2.4 ng/100 ml to 10.5 +/- 1.5 ng/100 ml on the final day of high Na intake. 4. We conclude that increases in P[Na] in the absence of concomitant changes in P[K], 22Na space and MAP do not have a sustained effect on control of renin release but may exert a negative effect on aldosterone secretion.

Control of canine renin release: macula densa requires prostaglandin synthesis

1. The macula densa mechanism of renin release was functionally isolated in uninephrectomized, anaesthetized dogs by producing renal denervation, beta-adrenoceptor blockade, and maximum renal vasodilation with an infusion of papaverine into the renal artery. 2. A suprarenal aortic clamp was adjusted to reduce renal perfusion pressure by 50% which resulted in a 90% reduction in urinary sodium excretion and a two to threefold increase in plasma renin activity within 10 min. 3. Indomethacin (8 mg/kg) or meclofenamic acid (10 mg/kg) inhibited the rise plasma renin activity produced by the decrease in renal perfusion pressure in this model, although a comparable decrease in urinary sodium excretion was achieved. 4. We conclude that the macula densa mechanism of renin release is blocked by inhibition of prostaglandin synthesis.

[Cyclic AMP and plasma renin activity in renal vein blood after amitryptiline, theophylline, furosemide and beta adrenergic blocking substances (author's transl)]

The influence of amitryptiline, theophylline and furosemide on the concentration of cyclic-AMP and plasma renin activity (PRA) was investigated in renal vein plasma. Additionally, the stimulating effect of furosemide on the PRA after application of the beta-adrenergic receptor antagonists propranolol and practolol and the cyclic AMP concentration in the plasma were measured. All drugs were given intravenously. After amitryptiline cyclic-AMP concentration increased about 1.5-fold compared with the basal value,PRA was not altered. After theophylline cyclic-AMP concentration increased about 1.2-fold, PRA 2.0-fold compared with the basal value, PRA was not altered. After theophylline cyclic-AMP concentration increased about 1.2-fold, PRA 2.0-fold coa increased within 7 min and no further increase was observed till the 15th min. After practolol cyclic-AMP concentration and PRA decreased about 20% compared with the basal value within 10 min. The stimulating effect of subsequently applied furosemide on PRA was not altered, but the cyclic-AMP concentration was not changed in this time by furosemide. After propranolol cyclic-AMP concentration and PRA decreased about 20% compared with the basal value. The cyclic-AMP concentration was not influenced by the following furosemide application, in agreement with the findings after practolol, however, PRA could be stimulated only in 36% of these patients under beta-receptor blockade. Our results show that changes of the concentrations of cyclic-AMP and of PRA are independent of each other. An elevated intracellular cyclic-AMP level due to the inhibition of phosphodiesterase is as a single factor unable to stimulate renin release. Our results give no evidence of a direct involvement of the adenylcyclase-system in the mechanism of renin release. The effect of propranolol and practolol on the basal value of PRA and cyclic-AMP is equal. The different influence of 10 mg propranolol and 20 mg practolol on the stimulating effect of 40 mg furosemide on the PRA can be interpreted as a dosage problem.

Sensitive osmometer function of juxtaglomerular cells in vitro

The rate of renin release from viable juxtaglomerular cells was studied during prolonged superfusion of isolated rat renal glomeruli with Ringer solutions of differing osmolarities. 2. Reduction in osmolarity from 305 to 285 m-osmole/l. by lowering sucrose concentration caused renin release rate to double. A rise in osmolarity of 30 m-osmole/l. by raising sucrose concentration halved release rate. 3. The response to osmolarity was graded. During the first 30 min following a 20 m-osmole/l. decrease in osmolarity, 1-57 +/- 0-22% (S.E. of mean) of cellular renin content was released; three times this amount was released with a decrease of 50 m-osmole/l. The effect persisted at lower release rates for 60-90 min. 4. The juxtaglomerular cells were four to five times more sensitive to changes in osmolarity through sucrose than sodium chloride concentration. Changes in potassium chloride concentration (7-57 mM) had little effect. 5. Sodium chloride had no direct ionic effect on renin release outside its osmotic properties. 6. The findings support a previous proposal that the rate of renin release in vitro relates directly to the volume of the juxtaglomerular cell. The hypothesis is developed that a similar mechanism may underlie renin secretion in vivo.

Influence of ethacrynic acid on intrarenal renin release mechanisms

Ethacrynic acid infused i.v. in anesthetized dogs after inhibiting sympathetic mechanisms of renin release increased renal blood flow rate (RBF) by 54% and practically abolished autoregulation of RBF; renin release increased from 0.8 +/- 0.9 (mean +/- SEM) to 16.4 +/- 3.7 mug/min (P less than 0.05). Without infusion of ethacrynic acid; constriction of the renal artery to a pressure below the range of autoregulation reduced renovascular resistance markedly and renin release rose to 27.2 +/- 5.5 mug/min (P less than 0.05). During arterial constriction, ethacrynic acid had no additional effect on renovascular resistance or renin release averaging 28.4 +/- 6.7 mug/min. Infusion of ethacrynic acid and saline at control pressure increased sodium excretion to about one-half of the filtrate and reduced rein release which did not, however, return to control. Infusion of hypertonic saline during autoregulated vasodilatation induced by arterial constriction had a similar effect, but again renin release continued to exceed control. We propose that ethacrynic acid increases renin release through a hemodynamic mechanism triggered by afferent arteriolar dilation and inhibits renin release by greatly increasing the delivery of sodium to the distal convoluted tubules.

A specific role for saline or the sodium ion in the regulation of renin and aldosterone secretion

It is well established that in normal man the renin-angiotensin-aldosterone system is responsive to changes in volume. The present study was performed to determine whether sodium has an action apart from volume in the regulation of the secretion of renin and aldosterone. Acute volume expansion was induced either by saline, dextran, or glucose infusion in supine, normal subjects in balance on a 10 meq sodium/100 meq potassium diet. Plasma renin activity (PRA), angiotensin II (A II), aldosterone (PA), cortisol, serum sodium, and potassium were measured every 10 min for the first 30 min and then at 1, 2, 4, 6, and 8 h. During saline infusion (500 cm(3)/h for 6 h) mean PRA and A II levels declined very rapidly, falling significantly below control at 10 min (P < 0.01) and by 50% at 60 min. Thereafter, the rate of fall was more gradual, reaching a nadir at 360 min (70-80% below control). PA declined in a parallel pattern except that a significant fall did not occur until 30 min. In contrast to saline, dextran infusion (250 cm(3)/h for 4 h) did not produce a significant fall in PRA, A II, or PA until 4 h after the start of the infusion despite equivalent volume expansion. On the other hand, the infusion of 5% glucose and water (500 cm(3)/h for 6 h) did not produce a significant decline in PRA, A II, or PA over the first 6 h of the study. Although the response rate of PRA, A II, and PA was different in each of the three infusion studies, these parameters were significantly correlated within each study. Serum sodium and potassium levels did not change during any study except dextran infusion, where a significant fall in both occurred at 120 min. In all the infusion studies, plasma cortisol levels gradually declined during the 8-h study period consistent with its expected rhythm of diurnal secretion. These results demonstrate that rate of response of the renin-angiotensin-aldosterone system to acute volume expansion with saline differed from that with dextran and glucose infusion in sodium-depleted man. The data support a specific role for volume expansion with saline or the sodium ion per se in the regulation of renin and aldosterone.

Renin responses to water restriction and rehydration

1. The effect of restricted water intake and rapid rehydration was studied in three conscious sheep with respect to plasma renin concentration (PRC), blood corticosteroid levels, plasma protein and electrolyte concentrations, and the renal and faecal excretion of sodium and potassium.2. During water restriction the plasma concentrations of renin, protein and sodium rose while aldosterone levels were low or undetectable. Plasma potassium levels were unchanged. External sodium and potassium balance appeared to be unaffected.3. During rehydration the sheep drank more than their estimated water deficit in 3-4 min with the following effects: PRC rose three- to fourfold during the ensuing 12 hr. Aldosterone levels too rose, while plasma protein, sodium and potassium concentrations fell. Urinary sodium excretion virtually ceased for 24 hr, and urine flow rate increased only little during this period.4. If there was a single stimulus to renin release during water restriction and rehydration, it was not an alteration in vascular or extravascular volume, total body sodium, systemic B.P. or plasma sodium concentration.5. It is concluded that the rise in PRC in these experiments is compatible with the theory that altered sodium transport at the macula densa was the stimulus for renin release.