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An endothelium-derived relaxing factor has been identified as nitric oxide (NO). Peripheral and central administration of nitric oxide synthase inhibitors result in an increase in renal sympathetic nerve activity and an increase in blood pressure. The goal of our study was to determine if the increase in blood pressure following central NO synthase inhibition with N omega-nitro-L-arginine (L-NNA) is caused by the release of renin. Six groups of Sprague-Dawley rats were used. Group I (control) received intracerebroventricular (i.c.v.) artificial cerebrospinal fluid. Groups II & III received i.c.v. L-NNA, 5 & 15 micrograms/min. respectively. Group IV was treated with intravenous L-NNA, 15 micrograms/min. Group V, after bilateral nephrectomy, received i.c.v. L-NNA, 15 micrograms/min. Group VI received i.c.v. L-arginine, 60 micrograms/min. and i.c.v. L-NNA, 15 micrograms/min., simultaneously. Plasma renin concentration was measured in groups I, III, IV & V. Mean arterial blood pressure was significantly increased in groups II, III & V, i.e., following i.c.v. infusion of L-NNA. The increase in mean arterial blood pressure was significantly greater when the dose was increased from 5 to 15 micrograms/min. and it was eliminated when L-arginine was added to the infusion. The increase in blood pressure was attended by no change in heart rate. While the plasma renin concentration increased significantly in group III, this could not explain the increase in blood pressure since the nephrectomized group (V) showed no increase in renin concentration but an equivalent increase in blood pressure. The results show that acute central administration of a low dose of L-NNA increases blood pressure in rats and this increase can be prevented by central administration of L-arginine. However, intravenous infusion of the same dose (15 micrograms/min.) of L-NNA does not change blood pressure. We conclude that L-NNA acts directly within the central nervous system to increase blood pressure by a renin-independent mechanism. These results imply that central nitric oxide plays an important role in the regulation of blood pressure.

Renin secretion responds rapidly to a variety of stimuli; however, reported changes in renal renin messenger RNA (mRNA) levels in vivo have been observed only after prolonged stimulation. Studies were designed to test whether rapid changes in renin mRNA levels can be produced in vivo. In the first series, Sprague-Dawley rats received furosemide (10 mg/kg) intraperitoneally and a low sodium diet (0.05% sodium); renin secretion was significantly stimulated at 8 or 16 hours after treatment, but renin mRNA levels did not change. In a second series, rats were pretreated with deoxycorticosterone acetate (200 mg/kg) and saline drinking water for 3 days and then killed 0, 2, 4, 8, or 48 hours after furosemide administration. The renin mRNA level was unchanged at 2 hours but was stimulated twofold at 4 and 8 hours and threefold at 48 hours. In additional animals, the response of renin mRNA 4 hours after furosemide was found not to be potentiated by the converting enzyme inhibitor quinapril (5 mg/kg). The results demonstrate that with acute stimulation, renin mRNA levels lag 2-4 hours behind the change in plasma renin levels.

Active renin is a heterogeneous enzyme that can be separated into multiple forms with high-resolution isoelectric focusing. The isoelectric heterogeneity may result from differences in glycosylation between the different forms. In order to determine the relationship between active renin heterogeneity and differences in composition or attachment of oligosaccharides, two separate experiments were performed: (i) Tunicamycin, which interferes with normal glycosylation processing, increased the proportion of relatively basic renin forms secreted into the incubation media by rat renal cortical slices. (ii) Endoglycosidase F, which enzymatically removes carbohydrate from some classes of glycoprotein, similarly increased the proportion of relatively basic forms when incubated with active human recombinant renin. In addition, further studies with inhibitors of human renin activity revealed that the heterogeneous renin forms were similarly inhibited by two separate renin inhibitors. These results are consistent with the hypothesis that renin isoelectric heterogeneity is due in part to differences in carbohydrate moiety attachment and that the heterogeneity of renin does not influence access of direct renin inhibitors to the active site of renin.

Our laboratory demonstrated the existence of 6 forms of renin, (F1-F6) each with a unique isoelectric point (pI). We ascribe the heterogeneity to differences in glycosylation. This heterogeneity has been demonstrated to exist in all animals studied in our laboratory, across a wide evolutionary scale. Multiple forms have been found in fish, amphibians, birds and mammals, including humans. We have been able to demonstrate that hepatic inactivation of the renin forms in humans is different for each form. Isolation and purification of the forms allowed injection of a single form into rats. IV infusion of F4 resulted in a significant natriuresis and diuresis, while the other forms had no significant renal effects. However, if the same forms were infused into the cerebroventricles at a much lower dose, F6 caused a natriuresis. Pretreatment with converting enzyme inhibitor abolished that effect. We were able to show that Spontaneously Hypertensive Rats (SHR) exhibited a renin profile that was altered in a predictable way and was significantly correlated with their blood pressure. The hepatic clearance of each form was also different, so that the forms have different half lives. These data support the hypothesis that renin heterogeneity is dependent upon glycosylation and is functionally significant.

Renin heterogeneity has been described in rat kidney and plasma. In this study, we used the isoelectric focusing method to 1) characterize the adrenal renin forms in control rats, in rats on low- and high-Na diets, and in nephrectomized rats; and 2) examine their resemblance with plasma renin. Active renin (AR) and inactive trypsin-activatable renin (IR) were measured in adrenal homogenates and plasma. Aliquots were subjected to isoelectric focusing gels. Activation with trypsin (5 mg/ml) was performed before or after isoelectric focusing. Results showed that adrenal glands contained AR and IR. The content of adrenal AR increased significantly only in rats fed a low-Na diet. Following anesthesia, nephrectomy, or high-Na intake, the content of adrenal AR and IR was not significantly changed. In plasma, an inverse relationship between AR and IR was found. Adrenal glands contained six forms of AR focusing at the same pH as those of plasma AR but in different proportions. After activation of IR in adrenal glands, two additional renin forms focusing at pH 6.4 and 6.1 were found, whereas after activation of plasma IR, two peaks focusing at pH 5.9 and 4.8 were significantly enhanced. Adrenal AR forms were modified by alterations of salt and water balance differently than plasma AR. These results support the hypotheses of an endogenous production of renin forms by the adrenal gland.

An electron microscopic study of the renal polkissen cells revealed evidence of their participation in the renin angiotensin system. An unusual feature of the cell is the presence of polar nuclear bags (vacuolization) with attached ribosomes. Significantly, a good correlation was observed between vacuolization and plasma renin activity. The latter was created by differing experimental settings, namely restricted sodium intake, hemorrhage, or reduced renal perfusion pressure. These data, plus the finding of secretory granules in these cells, are interpreted as evidence that the polkissen cells are in some way concerned with the regulation of secretion of renin.

Six forms of renin are found in the rat kidney. We studied their secretion in renal slices from spontaneously hypertensive stroke-prone rats (SHRSP) and Wistar-Kyoto rats (WKY). Incubation media from renal slices were subjected to isoelectric focusing. Six peaks of renin activity with different isoelectric points were found. The renin concentration of each form was expressed as a percentage of the total recovered from the gel. We established that the forms secreted by renal slices of SHRSP differed from those of WKY: SHRSP slices released a higher proportion of forms focusing at the more acidic pH. The distribution of the six renin forms and of blood pressure (BP) among animals of the F1, F2, and backcross progenies resulting from the cross of SHRSP and WKY rats were studied. In the F1, BP, percentage of renin form 2, and a combination of the percentage of forms 4 + 5 + 6 were intermediate between the parental lines. The backcross rats showed BP and percentages of forms closer to their SHRSP or WKY parent. In the F2, the distribution of BP, percentage of forms 2 and 4 + 5 + 6 take the form of a unimodal distribution with a significantly larger variance than F1. The increase in the correlation between percentage of renin forms and BP, and between renin concentration of BP, in the segregating progenies over that observed in the parental lines and the F1, are support for the hypothesis that these traits are under the control of common genetic mechanisms.

The alteration of renin release by alpha- and beta-adrenoceptors located on the juxtaglomerular cells has been shown to be temperature sensitive in nonhibernating mammals. These experiments investigate the effects of temperature on renin secretion by cortical slices of kidneys from the thirteen-lined ground squirrel Spermophilus tridecemlineatus. At 37 degrees C, beta-stimulation (isoproterenol 10(-7) M) increased the release of renin by slices taken from nonhibernating ground squirrels but had no effect on those taken from hibernating squirrels. The alpha-agonist phenylephrine (10(-5) M) had no effect on slices from nonhibernating squirrels but enhanced the release rate in those from hibernating ground squirrels, providing the first evidence of in vitro stimulation of renin release by an alpha-agonist. When incubated at 11 degrees C, kidney slices from both hibernating and nonhibernating animals were unresponsive to both alpha- and beta-agonists until incubation times were doubled. Under these prolonged conditions, phenylephrine again stimulated renin release. These results indicate that both in vitro and in vivo cooling alter the responses of alpha- and beta-adrenoceptors to renin-releasing stimuli.

Renal cortical slices from rat kidney were found to contain and secrete six forms of renin (EC 3.4.00.19). The multiple forms were demonstrated by an isoelectric focusing technique utilizing a stable, steady state pH gradient. The isoelectric points of the six secreted forms had the following pH values: 5.70, 5.55, 5.30, 5.15, 4.9, and 4.8, and represent, respectively, 1%, 62%, 17.5%, 8.5%, 8%, and 3% of the secreted renin. In the presence of isoproterenol (10(-6) M), renin secretion from the renal cortical slices was increased significantly (87%) over control (P less than 0.05). The increased renin secretion was accompanied by a significant change in the relative proportions of the six secreted forms of renin. These results indicate that multiple renin forms are stored and secreted by the rat kidney and that stimuli that increase renin secretion can preferentially increase the secretion of some of the multiple forms. It is hypothesized that isoproterenol stimulates the secretion of stored renin, which appears to be composed of a subset of the multiple renin forms.

Changes in the multiple forms of renin secreted or stored in vitro by renal cortical slices were studied in rats made hypertensive with deoxycorticosterone, adrenalectomized rats, and rats fed a high or low salt diet. Renal slices from normal rats were also incubated with angiotensin II, vasopressin, and verapamil. Aliquots of incubation media were subjected to isoelectric focusing, and the six forms of renin were quantified and expressed as a percentage of the total renin activity recovered from the gel. The results showed that chronic and acute stimulation of renin secretion produced a similar modification of the isoelectric focusing profile, consisting of an increased proportion of renin forms with the more acidic isoelectric points. The change in the proportions of the more acidic renin forms was greater with chronic stimulation than that after stimulation with verapamil. However, chronic and acute inhibition or reductions of the rate of renin secretion did not modify the renin profile. We suggest that the progression in the shift of secreted renin forms to those with the more acidic isoelectric points correlates with the intensity or duration of stimulation of renin secretion. These data support the hypothesis that different pools of renin exist and are altered differently by chronic and acute stimulation of renin secretion.

The in vivo and in vitro rates of renin secretion were measured in kidneys from five groups of dogs in which renal perfusion pressure, salt diet, and neural input were varied to cause large changes in renin secretion rates and renal renin content. It was found that both the in vivo and in vitro secretory rates were proportional to the renal renin content. However, in vitro secretion rates were dependent on content up to 100 ng angiotensin I/mg tissue per h. At higher renin contents no increment in in vitro secretion rate was seen. In vivo secretion rate did not appear to reach a maximum until renal renin content was above 250 ng AI/mg tissue per h. The data are interpreted to support the hypothesis that there exist at least two pools of renin. One releases renin at a fractional rate of about 1.5% of the total content per hour. The other releases renin at a rate dependent on the magnitude of the stimuli acting on the kidneys. It is also suggested that the rate of renin synthesis may be a determinant of the basla rate of renin secretion.

The effect of Ca concentrations in the incubation medium and of estimated intracellular Ca concentrations on renin release was examined with use of pig renal cortical slices. In addition, the Ca requirement for the epinephrine stimulatory effect and for the ouabain inhibitory action on renin release was also tested. In mediums containing 5.9 mM K, variations in Ca concentration had no effect on renin release. In contrast, when the K concentration was 59 mM, a significant inhibition of renin release was attained with all concentrations of calcium. The inhibition of renin release in high K mediums by Ca was attributed to an increase in the intracellular Ca concentration. In addition, both the stimulatory effect of epinephrine and the inhibitory effect of ouabain on renin release required Ca in the medium. These results support the hypothesis that the control of renin secretion is mediated, in part, by changes in the intracellular concentration of Ca, most likely in the juxtaglomerular cells.

This study was designed to evaluate the physiological importance of cardiopulmonary receptors with vagal afferents in controlling renin release during perturbations in blood volume. Intravascular volume of chloralose-anesthetized dogs was expanded by 7.5 ml/kg body wt, with an isotonic isoncotic solution containing 3% dextran for colloid. Volume expansion resulted in a 50% decline in renin secretion. However, volume expansion after bilateral cervical vagotomy, the proposed afferent limb of the reflex, also suppressed renin release. In another group of animals, the left kidney was surgically denervated and the right kidney extirpated, and again infusion suppressed resin release. In all groups, the infusion significantly suppressed renin release when compared to each dog's own control period, as well as when compared to the corresponding time controls. Our data indicate that the renin response to intravascular volume expansion was not mediated solely by the vagi or renal nerves. A combination of intrarenal factors may, however, have been responsible for the suppression of renin release observed. Our results do not support the hypothesis that the renin-angiotensin system is an efferent limb of the cardiopulmonary reflex during adjustments to alterations in blood volume.

Six distinct forms of renin were found to be released from rat renal cortical slices incubated in vitro. The multiple renin forms were demonstrated using shallow gradient isoelectric focusing, and focused at pH 5.7, 5.55, 5.3, 5.15, 4.9 and 4.8. Before renal cortical slices were prepared, rats were given free access to both high- and low-salt diets containing, respectively, 0.2 or 0.005 mEq Na+/g food. Renal cortical slices prepared from rats maintained on the high-salt diet for 8 days (group I) released significantly different proportions of the six renin forms as well as less total renin when compared to rats first maintained on the high-salt diet for 8 days followed by the low-salt diet for 8 additional days (group II). In a second series of experiments, renal cortical slices prepared from rats maintained on the low-salt diet for 19 days (group III) secreted significantly different proportions of the six renin forms, as well as more total renin when compared to rats first maintained on the low-salt diet for 10 days, followed by the high-salt diet for 4 additional days (group IV). These studies demonstrate that the relative proportions of released multiple renin forms change when the kidney alters its renin secretory rate in response to changes in Na+ intake.

Six dogs were implanted with chronic arterial and venous catheters and were trained to lie quietly on a padded table. The effect of pentobarbital anesthesia and of graded hemorrhage on plasma renin activity (PRA) was then examined in the absence of surgical stress. Pentobarbital anesthesia resulted in a fivefold increase in PRA within 15 min, followed by a slow decline to a level 3 times control at 1.5 h. Mean arterial pressure (MAP) fell transiently but returned to control values. In the unanesthetized dog, graded hemorrhage to 12 ml/kg resulted in a twofold increase in PRA with no change in MAP or heart rate. The same hemorrhage in pentobarbital-anesthetized dogs resulted in a similar increase in PRA, accompanied by a substantial increase in heart rate. It is concluded that 1) pentobarbital anesthesia in the dog results in a rapid and sustained increase in PRA, and 2) in the conscious dog, increased PRA in response to graded hemorrage appears to be independent of an arterial baroreceptor mechanism and of generalized increased sympathetic nervous system activity.

Six forms of renin, distinguishable by their isoelectric focusing characteristics, are found in rat kidney and plasma (forms 1-6, form 1 having the most basic pI). To test the hypothesis that high blood pressure in stroke-prone spontaneously hypertensive rats (SHRSP) is associated with a particular fraction of the renin forms, systolic blood pressure (SBP) and renin profile were measured in SHRSP, normotensive Wistar-Kyoto rats (WKY), and their genetic crosses (F1). Adult SHRSP showed an increase in the proportion of forms 4, 5, and 6 compared with WKY. F1 showed values between SHRSP and WKY. A strong positive correlation was noted between the fraction of the acidic forms of renin and SBP. The mean blood pressure and the fraction of the acidic renin forms in SHRSP and WKY pups also fitted the same regression line. However, no correlation existed between renal renin content (RRC) and SBP. SHRSP pups had a higher RRC than age-matched WKY or F1. RRC in normal adult SHRSP was lower than that in WKY or F1 of the same age. In old animals, SHRSP again showed the highest RRC, and microangiography of the kidney of old SHRSP revealed a loss of fine vascularity with few visible glomeruli. These results indicate that the established phase of hypertension in SHRSP is associated with an increased proportion of the acidic forms of renin, which may have a unique role in the establishment or maintenance of hypertension. It is also suggested that high RRC in the early developmental stage plays a role in the developing phase of hypertension.

Experiments were designed to clarify the factors affecting renin released during in vitro experiments. Kidneys from rat, dog, and pig were used. Experiments were done in which the gas phase was either bubbled through the incubation medium or layered above it. Renin released into the incubation medium disappeared very rapidly when gas was bubbled through the medium. The decline was similar in mediums bubbled with oxygen-CO2 (95%--5%) or nitrogen-CO2 (95%--5%). The half-life of renin activity in the bubbled medium was approximately 15 min in both cases. However, in experiments in which nonbubbled medium was used throughout, renin released into the incubation medium did not disappear after removal of slices. These data are interpreted to mean that the renin released into the incubation medium is inactivated at the air-water interface.

Hepatic clearance of renin in anesthetized dogs was measured during aortic constriction and after nephrectomy. Aortic constriction caused a transient increase in the hepatic extraction ratio for renin (ER) from 0.34 +/- 0.05 to 0.52 +/- 0.05, whereas nephrectomy caused the ER to decrease with time. Isoelectric focusing of plasma samples over an average pH gradient of 4.0-6.2 yielded several peaks of renin activity. Peaks focusing above pH 5.0 were combined and arbitrarily classified as basic renin, whereas peaks below pH 5.0 were classified as acidic renin. In each period the ER for basic renin was significantly greater than that for acidic renin. The proportion of basic renin was transiently increased at 10 min (59 +/- 4%) compared with control (41 +/- 4%). This contributed to the increased ER after constriction. The decreased ER after nephrectomy, however, was not solely due to differential removal of these forms. We conclude that hepatic clearance of renin is partly a function of the type of renin secreted by the kidney, which in turn may change with the duration of the secretory stimulus.

Rat renal slices were incubated in two different media. One was a normal K, physiological saline solution and the other a high K medium. Renin release was measured every 15 min in the presence and absence of 10(-6) M isoproterenol and also in the presence and absence of aspirin, 0.8 or 1.6 X 10(-5) M. In all experiments renin release was linear during the 75 min of incubation. Isoproterenol increased renin release by approximately 100%. This was the case even in the presence of aspirin which significantly inhibited prostaglandin release (PGE2, PGF2 alpha and 6-keto-PGF1 alpha). Nor was there any reduction in the basal secretory rate by aspirin alone. These data are taken to indicate that aspirin in pharmacological doses does not interfere with either in vitro basal release rates of renin, nor the response to B agonists. It is also suggested that B agonists do not exert their effect by stimulating prostaglandin secretion.

The release of newly synthesized renin by dog renal cortical slices was investigated. A radioactive protein believed to be renin was secreted from cortical slices into an incubation medium containing radioactive leucine. The nature of the radioactive protein was established by dialyzing the incubation medium after the cortical slices were removed, and subsequently applying the dialysate to 15% discontinuous polyacrylamide gels. Renin activity in the gels comigrated with the labeled protein. The labeled protein, as evidenced by a peak in 3H or 14C disintegrations per min, also comigrated with renin activity in isoelectric focusing gels. The molecular weight of the labeled protein was found to be the same as renin, approximately 40,000. Cortical or medullary slices possessing little or no renin activity did not secrete the labeled protein into the incubation medium. Isoproterenol significantly increased total renin secretion from the slices, but not the secretion of newly synthesized renin. The data support the hypothesis that two or more pools of renin are available for release. One pool releases newly synthesized renin, while another pool releases older, possibly stored renin, dependent in part on the stimuli available for renin release.

Six forms of renin with different isoelectric points (pIs) have been described in rats. This study was designed to determine if any of the renin forms have different biological activities. Each form of rat renin was semipurified and injected intravenously or intraventricularly in Sprague-Dawley rats anesthetized with pentobarbital sodium or Inactin. Changes in blood pressure (BP), renal function, sodium, and water excretion were observed, before and following equipressor doses; the peak response of BP was similar for all forms. However, the half-lives were significantly different. Form 4 (pI = 5.2) caused a significant increase in urine flow, Na, and K excretion, and urinary osmolality when given intravenously. The other forms were without significant effect. Infusion of converting enzyme inhibitor not only completely blocked the BP response, but also prevented the natriuresis and diuresis. This was observed in rats anesthetized with pentobarbital sodium or Inactin. Intraventricular infusions resulted in a diuresis and natriuresis when form 6 (pI = 4.8) was infused, but not with other forms. BP remained unchanged throughout. This study presents evidence that functional differences exist between renin forms.

The release of renin from dog cortical kidney slice preparations incubated in a physiological salt solution can be modulated by alpha- and beta-adrenergic drugs. When given to slices maintained at 37 degrees C, the beta-agonists isoproterenol (ISP) and norepinephrine stimulated renin release from the slices. When the slices were maintained at 20 degrees C, the beta-agonists had no effect on renin release. However, the alpha-agonist phenylephrine inhibited renin release from the slices incubated at 20 degrees C in a dose-dependent manner, whereas its effect on slices incubated at 37 degrees C was less pronounced. The change in response of the slices from beta dominant at 37 degrees C to alpha dominant at 20 degrees C appeared to be a receptor phenomenon. When the cortical slices were incubated with the irreversible alpha-antagonist phenoxybenzamine (POB) at 20 degrees C for 1 h, they were unable to respond to ISP when returned to 37 degrees C. However, POB had no effect on the response of slices to ISP when given at 37 degrees C. It appears that with a decrease in temperature the renal beta-receptors demonstrate properties normally associated with alpha-receptors, namely the potential to be blocked by POB. This may be due to an interconversion of the renal alpha- and beta-adrenoceptors.

Rat kidney contains six forms of renin, which are in different proportion from those found in plasma. We tested the hypothesis that differential removal and production of the forms might explain the differences between stored and circulating renins. In one group of rats, the six forms of renin were measured in plasma, 10 min after hemorrhage, or after aortic constriction. Plasma was run on an isoelectric focusing gel, and the six peaks of renin activity were expressed either as angiotensin I per hour per milliliter or as a percentage of the total plasma renin concentration. After hemorrhage or aortic constriction, the concentration of each form was significantly increased; the profile of circulating renin was significantly modified, showing an increase in proportion of form 2 and a decrease of forms 4, 5, and 6. In a second group, the disappearance of each form was measured 0 to 100 min after nephrectomy and fitted a two-exponential decay curve. Interpreted as a two-pool system with degradation from pool 1, the degradation rate decreased progressively, going from form 1 to 6. In a third group, arterial and renal venous blood were collected. The profile of secreted renin was calculated from the arterial venous difference. This profile fitted the prediction of the two-compartment model. Our data support the hypothesis that the proportion of each circulating renin form is the result of a balance between the rate of production of renin of constant composition and the degradation of the six forms at different rates.

We previously demonstrated the presence of six active forms of renin in rats, based on their isoelectric points (pI). Intravenous or intraventricular injections yielded different renal effects with the different forms. Additional work is presented supporting the hypothesis that these forms are functionally different. Renin form 2 (pI = 5.7), form 4 (pI = 5.2) or form 6 (pI = 4.8) was infused intravenously (IV) in Spague-Dawley rats. The total renin infused over 30 minutes was the amount that could generate 1000 ng angiotensin I (Ang I)/h/100g body weight. Arterial blood pressure, urine volume, sodium, and potassium excretion were determined at 15-minute intervals. Plasma renin activity (PRA) and plasma aldosterone concentrations were measured 45 minutes after the start of infusion of renin forms. Infusion of renin form 4 increased urine volume and sodium excretion significantly. Renin forms 2 and 6 were without effect on renal excretion in spite of the fact that the same activity was infused. Both PRA and aldosterone concentrations after renin infusions were similar for all groups. Nonrenin renal protein with the same pI as form 4 was used as a control. This preparation was inactive and implies that our data with renin form 4 were not the result of contamination with a nonrenin protein having a pI of 5.2. In addition, the urinary responses could not be attributable to change in renal perfusion pressure as arterial blood pressure was not altered. These data support the hypothesis that there are functional differences among the different renin forms.

Rat renal cortical slices incubated in vitro released 7.0 +/- 0.5% (mean +/- SE, n=30) of their total renin content into the incubation medium in 1 h. Isoproterenol (10-6 M), a beta-adrenergic agonist, caused a 75 +/- 17% (n=7) increase in renin release from the cortical slices. Treatment of the cortical slices with either cycloheximide or puromycin caused a significant 96.2 +/- 0.34 (n=8) or 98.5 +/- 0.3% (n=5), respectively, inhibition of protein synthesis. After protein synthesis and presumably renin synthesis was blocked with either cycloheximide or puromycin, isoproterenol was still able to increase significantly renin release from the cortical slices despite almost total blockade of protein synthesis. We conclude that a storage pool of renin content is released may exist, since 1) only 7.0 +/- 0.5% of the cortical slice renin content is released each hour, and 2) isoproterenol stimulation of renin release is not acutely dependent on renin synthesis. It is hypothesized that beta-adrenergic stimulation of renin release is elicited from a storage pool of previously synthesized renin.

Six forms of renin have been described in rat kidney. Different stimuli resulted in secretion of unique profiles of those forms. We studied their storage and secretion in the two-kidney, one-clip Goldblatt hypertensive rat (GHR). Renal venous blood, kidney homogenates, and incubation media from cortical slices were subjected to isoelectric focusing. In all samples tested, six peaks of renin activity were found with isoelectric points at pH 5.90, 5.70, 5.40, 5.20, 5.00, and 4.80. The quantity of renin activity for each form was expressed as a percentage of the total recovered from the gel. In control kidneys the profile of renin stored and that released by in vitro slices were similar. However, in plasma, the percentage of renin focusing at the more basic pH was decreased. This is in agreement with other work showing that the liver removes the more basic forms more rapidly than the acidic forms. The clipped kidney of GHR secreted, both in vivo and in vitro, a profile of renin forms that was significantly different from the control kidney. The difference was expressed by an increase in the secretion of the more acidic forms by the clipped kidney. It is hypothesized that changes in the secretory profile of renin may reflect changes in storage and synthesis of those forms.