Extraction, purification, and assay of human renin free of angiotensinase

Partial purification of dog angiotensinogen

Dog angiotensinogen was purified 450-fold from the plasma of nephrectomized dogs by a simple four-step procedure involving precipitation between 1.5 and 2.3 M ammonium sulfate, gel filtration on Sephadex G-150, ion-exchange chromatography on DE-52 cellulose, and affinity chromatography on Concanavalin A-Sepharose. The purity of the final preparation was over 50%. The preparation of dog angiotensinogen had an apparent molecular weight of 80,000 determined by gel filtration on Sephadex G-100. Kinetic studies indicated that the Km of the reaction of dog renin with partially purified dog angiotensinogen (1,840 pmol/ml) was similar to that for the reaction with angiotensinogen in diluted dog plasma (1,820 pmol/ml). Thus the purification procedures employed did not alter the affinity of dog renin for the Leu10-Leu11 bond of dog angiotensinogen. Because the concentration of angiotensinogen in dog plasma is about 700 pmol/ml, a first order reaction with respect to substrate is indicated in vivo.

Effects of angiotensin II and angiotensin II antagonist saralasin on cell growth and renin in 3T3 and SV3T3 cells

Components of the renin-angiotensin system were studied in established cell culture lines of 3T3 and SV3T3 mouse fibroblasts. The renin content in 3T3 cells was significantly higher than in virus-transformed SV3T3 cells. With time after infection, renin decreased in Simian virus 40 transformed cells, while it increased steadily in mock-infected 3T3 cells. In contrast to renin, angiotensinase activity was higher in SV3T3 cells. Angiotensin II stimulated cell proliferation in 3T3 mouse fibroblasts and decreased their renin content in a dose-related manner. In contrast, saralasin, an angiotensin receptor antagonist, inhibited cell growth in 3T3 and SV3T3 cells and caused an increase of cellular renin concentration. The angiotensin fragments angiotensin (2-8) heptapeptide and angiotensin (4-8) pentapeptide had no effect on cell growth. A significant negative correlation was found between cell proliferation and renin levels in 3T3 and SV3T3 cells irrespective of the treatment. Our results indicate (1) that angiotensin II may be involved in cell growth regulation, (2) that a negative feedback exist between angiotensin II added and intracellular renin content, and (3) that virus infection causes a decrease in intracellular renin synthesis, while non-specific angiotensinase activity is increased under this condition.

Properties of the activation by pepsin of inactive renin in human amniotic fluid

1. The renin present in human amniotic fluid was found to have an apparent Mr of 58 000 by gel filtration and is thus bigger than renin in untreated kidney extracts and plasma (Mr approximately 40 000). 2. Treatment with pepsin (40 microgram/ml pH 4.8, 2 h, 22 degrees C) caused a 6-fold increase in activity of this renin species, although Mr was not very different (57 000). 3. Unlike renal renin, renin in human amniotic fluid was not a glycoprotein and behaved similarly on concanavalin A-Sepharose before and after activation by pepsin. 4. Ion-exchange chromatography demonstrated a small change in the ionization properties of human amniotic fluid renin after activation by pepsin. 5. Pepsin-mediated activation resulted in a five-fold increase in V, but only a small decrease in the Km of renin to 39% of normal, so that the increase in activity observed was not due to an increase in the affinity of the enzyme for its substrate. The kinetic data were consistent with the theory of noncompetitive inhibition. 6. The activation of human amniotic fluid renin by pepsin may be caused by a change in the tertiary structure of the molecule subsequent to a proteolytic action that does not remove detectable polypeptide components.

Plasma renin substrate sensitivity to oestrogens and oestrogen metabolism in cirrhosis

Oestrogen stimulation of plasma renin substrate (PRS) was studied in men with alcoholic cirrhosis. PRS values, before and 1, 2, 4 and 6 days after a single oral administration of 100 microgram of an oestrogen derivative, 11beta-methoxy-17-ethynyl-1,3,5(10)-estratriene-3,17beta-diol (Moxestrol), were measured by radioimmunoassay of generated angiotensin I in five men with normal liver function and five men with alcoholic cirrhosis. Basal PRS was 0.93 +/- 0.22 nmol/ml (mean +/- 1 SD) in the normal men and significantly lower (P less than 0.01) in the men with cirrhosis (0.33 +/- 0.14 nmol/ml). Two days after administration of Moxestrol, PRS rose significantly but transiently (P less than 0.05) to 1.41 +/- 0.42 nmol/ml in the normal men and to 0.47 +/- 0.15 in the cirrhotic men, the relative increase (approximately 50%) being similar in both groups. A study of the plasma kinetics and urinary excretion of Moxestrol was also performed to evaluate its metabolic clearance rate and absorption. Since the intestinal absorption of [14C] Moxestrol was not depressed in cirrhotic men, the low PRS values recorded are probably the consequence of hepatocyte dysfunction.

Multiple forms of human plasma renin substrate

The objective of this investigation was to determine whether heterogeneity of plasma renin substrate could be observed in states of steroid excess and various forms of hypertensive disease. In states of stimulated renin substrate production by estrogens or glucocorticoids, multiple forms of renin substrate were apparent when stimulation was excessive. Stimulation of substrate production caused by uremia associated with hypertension showed similar results. None, or only trace quantities of the additional forms of renin substrate were evident in subjects with normal or suppressed levels of plasma renin substrate. The additional forms of renin substrate could be distinguished from the normal form on the basis of cross-reactivity with a specific antiserum to the normal form, electrophoretic mobility, and kinetic rate constants. Differences in rate constants of the various forms of plasma renin substrate may account for the altered rate of the renin reaction associated with several states of hypertension. In plasma of patients with renovascular hypertension, significant quantities of a protein which cross-reacted with the antiserum but could not generate angiotensin I were observed.

In vitro and in vivo inhibition of renin by fatty acids

Circulating neutral lipids inhibit the in vitro renin reaction. To identify the inhibitor(s), free fatty acids were added to human renin and homologous substrate. Capric, lauric, palmitoleic, linoleic, and arachidonic acids each inhibited the rate of angiotensin I production in vitro (P less than 0.01). Inhibition by polysaturated fatty acids (linoleic and arachidonic) was less (P less than 0.01) after catalytic hydrogenation of the double bonds. To evaluate an in vivo effect of renin inhibition intra-arterial blood pressure responses to infusions of renin and angiotensin II (5.0 microgram) were measured in anephric rats (n = 6) before and after infusion of linoleic acid (10 mg iv). Mean increase of blood pressure to angiotensin II before (75 mmHg +/- 9) and after (90 +/- 12) linoleic acid did not differ (P greater than 0.05). However, the pressor response to renin after linoleic acid (18 +/- 3) was less (P less than 0.00)) than that before (102 +/- 13). In summary, several fatty acids inhibit the in vitro renin reaction, and in part inhibition is dependent on unsaturation. Linoleic acid also inhibits the in vivo pressor response to renin. These results suggest that fatty acids may modify the measurement of plasma renin activity and may also affect angiotensin production in vivo.

Separation of human renal renin and pseudorenin by affinity chromatography on hemoglobin-Sepharose-2B

Human renal renin (EC 3.4.99.19) and pseudorenin were easily separated in a single step by affinity chromatography on hemoglobin-Sepharose-2B. Renin and pseudorenin were monitored by their actions on crude and partially purified hog protein renin substrates at neutral and acidic pH and on synthetic labelled polymeric renin substrate. Under the conditions employed (0.1 M sodium acetate (pH 3.5)/1 M sodium chloride at 4 degrees C) renin does not bind to the affinity adsorbent while pseudorenin is effectively bound and can be eluted only after raising the pH to 6.5. Pseudorenin-free renin prepared by this method is devoid of proteolytic activity toward hemoglobin. The chromatographic behaviour of renal pseudorenin on hemoglobin-Sepharose-2B is similar to that of cathepsin D.

Antidiuresis induced by beta1- and beta2-adrenergic agonists in ethanol-anesthetized rats

The beta1- and beta2-components in antidiuresis and sodium retention induced by beta-adrenergic agonists were analysed in ethanol-anesthetized, water-diuretic rats. Intravenous infusions of isoprenaline, salbutamol and carbuterol did not affect insulin clearance but increased plasma renin concentration to the same same extent. Propranolol completely blocked the decreases in urine volume (V) and urinary sodium excretion (UNaV) induced by isoprenaline; practolol (beta1-blocker) inhibited only the decrease in UNaV and butaxamine (beta2-blocker) inhibited only the decrease in V. The ratios of doses of beta-agonists which decreased UNaV and by 50% (ED50 UNaV decrease/ED50 V decrease) were 0.34, 0.68, 1.56 and 2.36 for isoprenaline, tretoquinol, salbutamol and carbuterol, respectively. This increasing order of the ratios coincided with the order reported for the preponderance of the beta2- over beta1-component of these agonists. These results indicate that the decrease in UNaV induced by beta-agonists is related to beta1 stimulation, while the decrease in V is related to beta2 stimulation.

Renin and the juxtaglomerular apparatus in diabetic nephropathy

In order to study the role of the renin-angiotensin system in patients with diabetic nephropathy, renin release and the juxtaglomerular apparatus were studied in 17 diabetic patients with proteinuria and in 23 without proteinuria; 8 normal subjects were used for conctrls. Despite hypertension and marked arteriosclerosis, plasma renin activity (supine posture) was normal; however, the renin response to salt restriction and upright posture was less in the diabetic patients with proteinuria than in the controls. Renal renin content, determined at autopsy, was also normal. Examination of the juxtaglomerular apparatus in the diabetic patients with proteinuria revealed hyalinization of the afferent and efferent arterioles in most of the glomeruli and various degrees of destruction of the juxtaglomerular cells. The findings suggest that renin production is not increased in diabetic patients with proteinuria plus marked vascular damage, and that the renin-angiotensin system in patients with diabetic nephropathy apparently does not play an important role in the exacerbation of hypertension or the degree of vascular damage.

Evidence for the glycoprotein nature of kidney renin

The glycoprotein nature of renin isolated from either rabbit or human kidney has been demonstrated by affinity chromatography on concanavalin A-Sepharose. The bulk of rabbit renin activity bound to concanavalin A is released by 20 to 50 mM alpha-methyl-D-mannoside. Adsorption of renin is prevented by periodate oxidation prior to chromatography. Mild acid treatment (pH 2.5) prior to chromatography does not alter the concanavalin A binding profile although the pI values of native rabbit renin (5.1-5.6) are shifted into a broader distribution (4.7-6.4). The molecular weight values of rabbit renin obtained by gel filtration and those from zone centrifugation are identical (37000 +/- 1000), consistent with a low percent of carbohydrate in the glycoprotein. A hydrophobic contribution to the binding of renin by concanavalin A is evident since, in the presence of mM Ca2+ and Mn2+, higher concentrations of alpha-methyl-D-mannoside are required to affect the same release of renin at 23 degrees C compared to that at 4 degrees C. Furthermore, 25% ethylene glycol releases renin in the absence of alpha-methyl-D-mannoside. It is concluded that renin contains a small number of carbohydrate residues in relatively close proximity to a hydrophobic surface which enhances the interaction with concanavalin A.

On the specificity of human renin. Studies with peptide inhibitors

The amino acid sequence around the renin substrate site is known to be identical to the N-terminal tetradecapeptide: Asp-Arg-Val-Tyr-Ile-His-Pro-Phe-His-Leu-Leu-Val-Tyr-Ser. Renin (EC 3.4.99.19) from both primates and non-primates cleaves this peptide at the leucylleucine bond. Several analogs of the octapeptide segment: His-Pro-Phe-His-Leu-Leu-Val-Tyr of this tetradecapeptide act as competitive inhibitors for human renin with inhibition constants down to 1 muM. The same peptides were shown, however, to have no or only slight affinity for non-primate renin. The substrate site has been preserved throughout evolution whereas the enzyme site for human renin is different from that of non-primate renins. The findings suggest that species-specific peptides must be developed for both studies of renin inhibition and for renin purification.

Decrease in plasma noradrenaline levels following long-term treatment with prindolol in patients with essential hypertension

15 patients (4 females, 11 males, 21 to 55-year old) with mild to moderate essential hypertension (EH) were treated with placebo for two weeks and thereafter with increasing doses of prindolol (15 to 38 mg/day in the mean) and kept on a mean maintenance dosage of 32 mg/day for an average of 16 weeks in all. Blood pressure (BP), heart rate und plasma noradrenaline (PNA) concentrations were measured under standardized conditions (supine, standing, walking) at the end of two weeks on placebo and after the experimental treatment period. The results were compared to those of a group of 15 normotensive untreated control subjects (NS): after an average of 16 weeks on prindolol BP fell from 163/113 mm Hg to 129/91 mm Hg in the mean. PNA levels in EH before prindolol were significantly higher than in NS (supine: 272 +/- 22.0 ng/l (mean +/- SEM) vs. 135 +/- 15.1 ng/l, standing: 448 +/- 31.9 ng/l vs. 359 +/- 18.4 ng/l, walking: 388 +/- 22.5 ng/l vs. 234 +/- 22.1 ng/l). In EH chronic administration of prindolol led to a significant decrease in PNA concentrations under all the three test conditions to levels which did not differ significantly any more from those derived from NS. The adrenergic response to upright posture reflected in the percentage increase in PNA was significantly less in EH before prindolol when compared to the percentage increase in NS. On prindolol the adrenergic response was not abolidhed, yet it tended to approach the values found in NS. Before prindolol under resting conditions diastolic BP correlated closely with the corresponding PNA levels (p less than 0.01, r = 0.66, n = 15). This correlation could not be reestablished after prindolol treatment. The decrease in PNA after long-term treatment with prindolol was not correlated to the fall in blood pressure. The decrease in PNA indicates a lower activity of the sympathetic nervous system which may contribute to the antihypertensive effect of prindolol.

Methodologic problems in plasma renin activity measurements

The influence of pH and angiotensinase inhibitors on the in vitro generation of angiotensin I during PRA measurements has been investigated. PRA values obtained at pH 5.7 are higher than those obtained at pH 7.4. At pH 5.7, values obtained using diisopropylfluorophosphate (DRP 9 mM) as an angiotensinase inhibitor are higher than values obtained with a mixture of dimercaprol (BAL, 1.6 mM) and hydroxyquinoline (8-OHQ, 3 to 4 mM). Since the two methods for inhibiting angiotensinase are completely and equally efficient, it is suggested that these inhibitors might interfere with the renin angiotensinogen reaction. Significant correlations are observed between the PRA values obtained by the different methods which have been studied. Using an incubation pH of 5.7, and BAL and 8-OH quinoline as angiotensinase inhibitors, the distribution of PRA values in a population of 124 hospitalized hypertensive patients ingesting a normal sodium diet had been studied, and it has been demonstrated that the sensitivity of this method of measurement can detect small changes in PRA in patients with low renin activity.

Partial purification of human renin substrate

A two-step purification method is described for the preparation of renin substrate from human plasma. Pooled plasma from women on oral contraceptives is used for the purification. The overall yield of renin substrate is 57%, with a twenty-fold purification. The specific renin substrate content of the preparation, as determined by enzymatic degradation with an excess of human renin, is 2 mug angiotensin I per mg protein. The product has a very low endogenous renin activity and is free from angiotensinase activity. An additional purification step involving affinity chromatography is described. In pilot studies a renin substrate yield of 37% has been achieved, with a hundred-fold purification. The final product has a specific renin substrate content of 10 mug angiotensin I per mg protein. The preparation contains up to 12 different plasma proteins, nine of which have been identified and quantitated.

[Diurnal profiles of plasma aldosterone, cortisol, renin, angiotensinogen and angiotensinases in normal subjects (author's transl)]

Plasma cortisol and renin were estimated in 1 h intervals, plasma aldosterone, angiotensinogen and angiotensinases in 3 h intervals over periods of 24 h in six normal volunteers (age 20-26) under control conditions and subsequently under suppression of ACTH release by dexamethasone. Highest cortisol levels were found around 7 a.m., minimum levels between 9 p.m. and 1 a.m. Dexamethasone reduced cortisol to constantly low concentrations. Aldosterone was highest around 4 a.m. under control conditions and under dexamethasone, and showed lowest concentrations between 4 and 10 p.m. There were no significant differences between mean aldosterone concentrations at corresponding time points of the control and the dexamethasone period. Similar to aldosterone, renen showed peak values around 4 a.m. All mean values at corresponding time points between 7 a.m. and 11 p.m. and the 24 hour mean values of each subject were significantly increased under the influence of dexamethasone. No evidence could be achieved for the existence of circadian rhythms of angiotensinogen and angiotensinases. Dexamethasone did not cause significant changes of these parameters.

Purification of canine plasma renin by affinity chromatography

An affinity column for the purfication of canine plasma renin was prepared using goat anti-renin (dog kidney) gammaG gloublins. The antiserum was prepared against a purified kidney renin preparation. The anti-renin globulins were coupled to cyanogen bromide activated Sepharose. Using the anti-renin globulin-coupled Sepharose as an immuno-adsorbant, a method was devised allowing purification of plasma renin to a 1,000-fold purity.

A possible role of the kidney in activating a renin preinhibitor

In order to verify the possibility than human plasma and kidney can activate a renin preinhibitor (Phospholipid) into inhibitor (lysophospholipid), constant quantities of preinhibitor were added to plasma and kidney homogenate. Addition of preinhibitor to plasma did not modify the quantity of Angiotensin I that developed. On the other hand, addition of preinhibitor to crude kidney homogenate, followed by incubation with human angiotensinogen, caused a significant fall in the quantity of Angiotensin I generated. While plasma is deficient in the specific enzyme delegated to the transformation of preinhibitor into inhibitor, it appears that this enzyme is present in the kidney.

Renin-angiotensin system in essential hypertension

In a random sample of normotensive and hypertensive fifty-year-old men plasma-renin-activity (P.R.A.), plasma-renin-concentration (P.R.C.), and renin substrate were measured using radioimmunoassay for angiotensin I. P.R.A. in normotensives and untreated hypertensives were normally distributed with slight skewness to the right. The mean P.R.A. for untreated hypertensives (0.65 ng. per ml. per hour) was slightly, but not significantly, lower than that of the normotensive reference group (0.78 ng. per ml. per hour). Previously untreated hypertensives who had been off treatment for four weeks had either high or low P.R.A. depending on the previous treatment. No differences in the angiotensin-generation rate were noted as judged from the P.R.A./P.R.C. ratio. No differences in the renin-substrate concentration between the groups were found. The findings suggest that renin changes in essential hypertenion are secondary to pressure changes. Thus, the renin-angiotensin system may not be of primary pathogenetic importance in the development of essential hypertension.

Improvement of renin determination in human plasma using a commonly available renin standard in a radioimmunological method

A new method for the measurement of renin in human plasma is described. The method is based on the introduction of the internationally available renin standard of the Medical Research Council (MRC) London, as a calibration system. Thus, some principal disadvantages of methods expressing results in renin reaction velocity (angiotensin generation rate) only are avoided. Both renins, unknown and standard, react with a sheep substrate preparation and are handled identically throughout the whole procedure including the angiotensin I radioimmunoassay (RIA). The plasma renin concentration (PRC) is given in 10(-6) MRC-renin units (muM/ml).

RESULTS

the renin standard is free of angiotensin, angiotensinases, and angiotensinogen; it is stable on storage. Identical enzyme kinetics are shown for both renins. An interference between endogenous and exogenous substrate could be avoided. The potentially harmful influences of proteins from the enzyme incubation mixture of the RIA dose response curve are shown. The use of an angiotensin I calibration system could be omitted. Using a standard renin dilution from 250-0.9 muU/ml also the full biological range is covered. When giving an unrestricted diet the preliminary normal values of PRC are 21.9 +/- 12.6 muU/ml in recumbent and 40.1 +/- 19.8 muU/ml in upright position (n = 16,x +/- s, age 20-35 years). Earlier findings of age-dependency of PRC were confirmed.

Reaction constants of renin in juxtaglomerular apparatus and plasma renin activity after renal ischemia and hemorrhage

Reaction constants of renin in juxtaglomerular apparatus and plasma renin activity after renal ischemia and hemorrhage. During and after total renal ischemia and acute hemorrhage, renin activity in plasma (PRA) and microdissected juxtaglomerular apparatus (JGA) of rabbits were investigated. In controls, the apparent Michaelis-Mentoen constant (MMC) of semipurified standard renin of rabbits was 1025 plus or minus 223 SD ng/ml. Plasma renin of normal rabbits showed similar values: 1062 plus or minus 138 SD ng/ml. Intrarenal JGA renin, however, showed a great scatter of MMC (920 to 4760 ng/ml) and a significantly higher mean value of 2572 plus or minus 1156 SD ng/ml (pis less than 0.001). After complete renal ischemia by clamping both renal arteries for a 90-min period, the following results wereobtained: 1) Sixty min after the beginning of ischemia, PRA decreased from 20.9 plus or minus 9.8 SD to 7.6 plus or minus 5.2 SD ng/ml-hr (P is less than 0.05) and increased to 103, 68 and 42 ng/ml-hr 10, 30 and 90 min after removal of the clamps, respectively (P is less than 0.05).

Effect of acute and chronic calcium administration on plasma renin

To evaluate the effect of Ca(++) on renin release, plasma renin activity (PRA) was measured after acute and chronic Ca(++) administration. 1% CaCl(2) was infused into one renal artery of 10 anesthetized dogs (0.3 mg/kg/min). The excreted fraction of filtered calcium (EF(ca++)) and EF(Na+) from the infused kidney were elevated (P < 0.04) during three successive 15-min infusion periods. Serum calcium concentration was significantly elevated (P < 0.001). Creatinine clearance, systemic arterial pressure, and renal blood flow did not change (P > 0.10). Compared to control (45 ng/ml/h+/-5.2 SE), renal venous PRA was suppressed (P < 0.0001) after infusion of Ca(++) for 15, 30, and 45 min (20 ng/ml/h+/-4.6, 16 ng/ml/h+/-4.0, and 13 ng/ml/h+/-2.7, respectively). 15 and 30-min after infusion, PRA did not differ from control (P > 0.20). Chronic Ca(++) loading was achieved in Sprague-Dawley rats by replacing drinking water with 1% CaCl(2) for 17 days. At sacrifice, serum Ca(++), Na(+), and K(+) of controls (n = 12) did not differ (P > 0.60) from Ca(++)-loaded rats (n = 12). Ca(++) excretion (467 mueq/24 h+/-51) was elevated (P < 0.001) compared to controls (85 mueq/24 h+/-12). PRA (8.6 ng/ml/h+/-1.4) and renal renin content of Ca(++)-loaded rats did not differ from controls (P > 0.80). However, after 8 days of sodium deprivation, both PRA and renal renin content of calcium-loaded animals were significantly lower than the respective values in pair-fed controls (P < 0.005). During the period of sodium deprivation, calcium-drinking animals were in greater negative sodium balance than controls (P < 0.005). The data are consistent with the hypothesis that acute and chronic calcium administration inhibit renin secretion.

Renin-like activity of the rat submaxillary gland: characterization and the effect of several drugs and stimuli

1. Renin-like activity was found in rat submaxillary glands.2. This activity was destroyed by boiling, was non-dialyzable and showed an optimum at approximately 50 degrees C.3. Renin-like activity in the submaxillary gland was not diminished 24 h after nephrectomy but was considerably reduced after ligature of the submaxillary duct.4. Renin-like activity in the submaxillary gland was reduced following food-deprivation, water-deprivation or hypovolemia.5. Renin-like activity in the rat submaxillary gland was increased after isoproterenol administration but not following pilocarpine.6. Renin-like activity in the rat submaxillary gland was increased considerably by administration of NaCl or KCl, as well as following adrenalectomy.7. Chlorothiazide and ouabain increased submaxillary renin-like activity but diazoxide did not affect this activity.