A rapid simple method for the assay of renin in rabbit plasma

Renin-angiotensin-aldosterone system in hyper- and hypothyroid rats during sodium depletion

A study was made of the responses of the renin-angiotensin-aldosterone system (RAAS) produced in hyper- and hypothyroid rats maintained in a state of sodium depletion, as part of a wider study to effect a comparison with results previously obtained for the same parameters in rats maintained on a normal sodium diet and during experimental alterations of thyroid function. In hyperthyroid rats maintained on sodium deficient and normal sodium diet, and in euthyroid animals on a sodium deficient regimen, elevations of both plasma renin concentration (PRC) and serum aldosterone concentration (AC) were observed, while the plasma renin substrate (PRS) was decreased. In hypothyroid rats with normal sodium intake, PRC and AC were observed to be decreased relative to similar sodium-deficient animals. Relationships were observed between PRC and AC, and between AC and urinary sodium excretion. These results suggest that: i) Sodium depletion is a more effective stimulus than the thyroid hormones on the RAAS. ii) Aldosterone changes in sodium depletion are mediated by the RAS. iii) Sodium depletion appeared to induce a decrease in the hepatic synthesis of angiotensinogen.

Capillaries of the adrenal cortex possess aminopeptidase A and angiotensin-converting-enzyme activities

The enzymes required to convert the prohormone angiotensin I into angiotensins II and III, secretagogues of aldosterone, are enriched in association with capillary endothelium isolated from rat adrenal cortex. Thus the secretion of aldosterone may be controlled, in part, by processing of peptides occurring within the adrenal gland itself.

Synthesis of renin substrate by rat liver

The present study attempts to determine if the isolated rat liver is capable of synthesizing renin substrate from 14C-labelled amino acids added in the perfusate. The renin substrate is characterized via reaction with renin, forming a substance that is subsequently identified as proangiotensin. Extensive evaluation of the reaction product is carried out by using molecular-sieve chromatography, countercurrent distribution, reactivity with converting enzyme, radioimmunological technique and bioassay. The results demonstrate that isolated rat liver perfused with artificial salt solution is capable of synthesizing a protein that reacts with renin to form a radioactive substance indistinguishable from proangiotensin.

A comparative study of the action of frusemide and methyclothiazide on renin release by rat kidney slices and the interaction with indomethacin

1 The effects of frusemide (a diuretic acting on the loop of Henle) and methyclothiazide (a thiazide diuretic) on renin release were studied on rat kidney slices. 2 Frusemide at concentrations of 1.5 and 7.5 mmol/l produced significant increases in renin release but had no effect at 0.15 mmol/l. 3 Methyclothiazide in a similar concentration range did not increase renin release; instead, at the highest concentration used, methyclothiazide (3.5 mmol/l) inhibited renin release. 4 Indomethacin (25 mumol/l) did not inhibit the increase of renin induced by frusemide. 5 Our limited study in vitro is consistent with the findings of other workers who have shown in vivo, in the absence of systemic electrolyte depletion, that only "loop diuretics" increase renin secretion. Under our experimental conditions, it is suggested that frusemide exerts a direct action either upon the epithelioid cells or upon the macula densa since the renal prostaglandin system does not intervene.

Characteristics and conversion of high molecular weight forms of renin in plasma and their incomplete activation by the current acid treatment

Two distinctly different high molecular weight forms of renin are present in mouse plasma in addition to the well-recognized active 40 000 dalton form. The biggest form has a molecular weight of about 800 000, and is stable in 4 M urea, but can be converted to the active 40 000 dalton form, by storage, exposure to acid and limited proteolysis. The 70 000 dalton form can be activated by acid and limited proteolysis. However, the 70 000 dalton form does not change molecular weight with activation. By measuring renin, not only by its enzymatic activity, but also by the direct radioimmunoassay for the renin molecule, which measures enzymatically active as well as inactive renin, it was found that both forms were activated but neither of them completely. The validity of the currently used term "total" renin as the enzymatic renin activity after acid activation, is, therefore, questionable. The quantitative significance of this must await methods which can ensure complete conversion or activation of the high molecular weight forms of renin in plasma.

Renin substrate in plasma of unanaesthetized pregnant ewes and their foetal lambs

1. In unanaesthetized preparations 6-14 days after catheterization, the concentration of renin substrate (AI 212 +/- 20 ng/ml. S.E. of mean) in the plasma of foetal lambs during the last third of gestation was significantly less than that of paired samples of maternal plasma (AI 350 +/- 27 ng/ml.). 2. During the first 5 days following catheterization the concentration of renin substrate in maternal plasma was lower than subsequently but was raised if the uterus contained a nephrectomized foetus. 3. The concentration of renin substrate in the plasma of intact foetal lambs without nephrectomized twins varied little in the post-catheterization period and later; the concentration of substrate in nephrectomized foetal lambs averaged threefold that of intact lambs and a similar concentration of substrate was found in intact twins of such lambs in the immediate post-catheterization period. 4. It is suggested that the ratio of foetal/maternal plasma renin activity understates their relative enzyme activity since foetal substrate concentration is so considerably less than maternal.

Treatment of Bartter's syndrome in early childhood with prostaglandin synthetase inhibitors

The diagnosis of Bartter's syndrome was made in a 9-month-old boy investigated for poor weight and height gain. Initial treatment with oral potassium supplements and later spironolactone had little or no effect on his growth, although plasma potassium rose to normal after spironolactone. At 33 months indomethacin therapy was started with dramatic results. His symptoms went and his height and weight accelerated into the normal range. In view of the toxicity of indomethacin it was replaced after 12 months by another prostaglandin synthetase inhibitor, ketoprofen, with a satisfactory result. During the change-over period from indomethacin to ketoprofen the expected deterioration in clinical well-being was observed, accompanied by a rise in urinary prostaglandins and plasma renin activity. Prostaglandin synthetase inhibitors provide the best available treatment for Bartter's syndrome.

Renin and aldosterone relationships in manic depressive psychosis

The paper describes a two-month period of study in four bipolar manic-depressive patients in a metabolic ward. Plasma renin activity, packed cell volume, plasma sodium and potassium were determined at intervals. Twenty-four-hour urinary sodium, potassium and creatinine were also estimated daily. Aldosterone production rate was measured on two occasions for each patient. Three of the patients showed at least one episode each of mania and depression during the study, while the fourth patient, who was receiving prophylactic lithium throughout, had one ten-day depressive episode but was otherwise normal. No obvious relationship between mood and plasma renin activity was observed, but the group showed a high resting renin activity, a blunted renin response to posture, and inappropriate aldosterone production rates for the renin activity found. It is postulated that a primary defect in the aldosterone-renin system may be present in bipolar manic-depressive psychosis.

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.

Simultaneous measurement of renin and renin substrate concentration in human plasma by a simple kinetic method

A simple kinetic method is described for measurement of plasma renin concentration (PRC) and plasma renin substrate concentration (PRS) in human plasma. It is based on the radioimmunological determination of angiotensin I generated when a plasma sample is incubated at 37 degrees C for 2, 4, 6 and 8 h. The use of exogenous renin and renin substrate preparations are not required. The specific velocity constant of reaction (K) was used to deduce the PRC. PRS determination was based on the stoichiometric conversion of renin substrate to angiotensin I. PRC and PRS have been determined in plasma from healthy subjects, plasma from health subjects 3 h after oral furosemide administration and in plasma from women, 12-20 weeks normally pregnant.

Effects of adrenaline, noradrenaline, isoprenaline and salbutamol on the production and release of renin by isolated renal cortical cells of the cat

1 Isolated renal cortical cells of the cat have been demonstrated to produce renin on incubation in vitro. After 2 h of incubation, without added agonist, the total amount of renin in the flask increased by a mean of 27.2 percent. The increase in renin content of the incubation flask was found to be present in the medium. 2 Noradrenaline (1.18 times 10-minus 4M) and adrenaline (1.09 times 10-minus 4M) added to the incubation medium stimulated renin production by 45 and 34% respectively, compared with the incubated controls. Most of the increase in renin production was present in the incubation medium. 3 Isoprenaline did not stimulate renin production. However, when added to the incubation medium at a concentration of 0.72 times 10-minus 4M there was a significant decrease in the cellular content and a significant increase in the medium content of renin. This increase was at least as great as that observed with adrenaline and noradrenaline. 4 Salbutamol had an effect similar to isoprenaline, i.e. it induced the release of renin into the medium without affecting production. In this respect it was about a third as potent as isoprenaline.

Cellophane perinephritis hypertension and its reversal in rabbits. Effect on plasma renin, renin substrate, and renal mass

Plasma renin activity and renin substrate levels were measured during the development of cellophane perinephritis hypertension induced by either a bilateral renal wrap procedure or a wrap-nephrectomy procedure in 28 rabbits. Unoperated and unilaterally nephrectomized controls were also studied. Plasma renin concentration was derived from plasma renin activity and plasma renin substrate levels using a measured K m of 2.3 x 10 -6 M. All surgical operations were followed by a transient increase in plasma renin substrate levels and a fall in plasma renin concentration. Unilateral nephrectomy in normotensive controls suppressed plasma renin activity and concentration for a 20-day period. Similar suppression occurred during the onset of hypertension in rabbits subjected to the wrap-nephrectomy procedure. Decapsulation accompanied by a fall in blood pressure again suppressed plasma renin activity and concentration. With bilateral wrapping, hypertension developed gradually without a change in renin levels. Decreased renin secretion during the evolution of perinephritis hypertension probably reflects a decreased renal excretory capacity for salt and water that overrides the renin-releasing effect of renal compression.

Effect of renal nerve stimulation, renal blood flow and adrenergic blockade on plasma renin activity in the cat

1. The effect of electrical stimulation of the distal cut ends of the renal nerves of unilaterally nephrectomized, anaesthetized cats was studied. Using stimulation parameters of 15 pulses per second (pps), 15 V and 0.2 msec duration, there was an immediate sharp drop in renal blood flow, as determined by an electromagnetic flowmeter, which was maintained for about 2 min. Flow gradually returned to control values over approximately the next 10 min in spite of continued stimulation for up to 30 min.2. Plasma renin activity (PRA) increased markedly after 10 min of stimulation but 20 min later fell towards pre-stimulation values whether stimulation was maintained or not.3. Phentolamine, an alpha-adrenergic-receptor antagonist, abolished both the blood flow and PRA responses to a 10 min period of renal nerve stimulation.4. When the renal artery was constricted in order to produce blood flow changes similar to those found with renal nerve stimulation, the rise in PRA was similar to that observed with renal stimulation.5. In phentolamine-blocked animals, renal artery constriction, as described, produced the same effect on PRA as was observed with renal nerve stimulation.6. Propranolol, a beta-adrenergic-receptor antagonist, did not block the blood flow response to renal nerve stimulation, but did block the rise in PRA normally associated with renal nerve stimulation.7. It is suggested that the effect of renal nerve stimulation on PRA is mediated, primarily, by changes in renal blood flow and that one of the steps leading to renin release following stimulation is sensitive to propranolol. This step must be distal to the effect on vascular smooth muscle.

Gaboon viper venom and its effects

Images

Plasma renin activity in the rabbit with renal hypertension

A method is described for the measurement of plasma renin activity (PRA) in the rabbit by radio-immunoassay of angiotensin I. PRA was measured in rabbits made hypertensive by the production of cellophane perinephritis and there was a significant increase in the activity of the enzyme after operation. It is argued that if renin had played no part in the genesis and maintenance of the elevated arterial pressure, then homeostasis would have depressed PRA below normal levels.

Renin excretion in patients with renal disease

The renal handling of renin was studied in normal subjects and in patients with predominant tubular and glomerular damage.

The renin in plasma and urine was assayed in the blood pressure preparation of the rat.

Excessive renin excretion occurred only in patients with proximal tubular dysfunction and was not related to creatinine clearance, proteinuria or plasma renin levels. However, a significant correlation was found between renin clearance and clearances of other low molecular weight proteins which pass freely through the glomerular membrane and are normally reabsorbed by the tubules. All the evidence points to the important role played by tubular reabsorption in the control of renin urinary excretion.

Properties of renin substrate in rabbit plasma with a note on its assay

1. Rabbit plasma enzymes that degrade angiotensin I are inhibited completely by the combination of 2,3-dimercaptopropan-1-ol (10mm), EDTA (10mm) and chlorhexidine gluconate (0.005%, w/v). These compounds do not modify the reaction of renin with renin substrate and are termed the selective inhibitors. 2. The renin substrate concentration of plasma can be measured as angiotensin I content by incubating plasma plus the selective inhibitors with renin for a time sufficient to allow complete utilization of renin substrate. 3. This reaction obeys first-order kinetics to substrate concentrations of at least 1000ng. of angiotensin I content/ml. In general, the renin substrate concentrations of normal rabbit plasmas are less than 1000ng. of angiotensin I content/ml. Thus the time required for the complete release of angiotensin I from normal plasma is inversely related to renin activity and is independent of renin substrate concentration. 4. A method for the assay of renin substrate, taking these reaction kinetics into account, is presented.