Renin release from isolated rat glomeruli

1. By the use of a mechanical graded sieving technique a high yield of isolated glomeruli has been obtained from rat kidny. 2. Microscopy and renin assay have shown the presence of renin-containing juxtaglomerular cells attached to these glomeruli. 3. The viability of isolated glomeruli has been confirmed by the ability of the cells to survive and divide in tissue culture and by their exclusion of vital dyes. 4. In superfusion after washout of extracellular renin, the glomeruli actively release constant amounts of renin over 3 h in direct proportion to the number of superfused. 5. Decreasing sodium concentration from 140 to 110 mol/l with constant osmolarity of 305 mosmol/l stimulated renin release by a direct effect on juxtaglomerular cells. 6. Catecholamines stimulated renin release in vitro in proportion to the potency of their action on beta-adrenoreceptors. 7. The system of superfusion of isolated glomeruli provides a technique for studying the influence of mediators leading to renin release acting directly on juxtaglomerular cells, independent of pressure change, tubular sodium, the sympathetic nervous system and circulating hormones.

Renin-angiotensin and kallikrein-kinin systems in sodium homeostasis and hypertension in rats

1. Urinary kallikrein excretion was measured in rats by an enzyme kinetic method employing radioimmunoassay of generated bradykinin. 2. Rats given a sodium load (NaCl solution, 20 g/l, to drink) for 28 days showed acute and prolonged significant falls in urinary kallikrein excretion associated with suppression of plasma renin and angiotensin. 3. Conversely sodium-depleted rats showed increases in urinary kallikrein excretion, associated with rises in plasma renin and angiotensin. 4. A close and significant direct relation between plasma renin activity and urinary kallikrein excretion was demonstrated. 5. The diuresis and natriuresis induced by frusemide in rats was associated with increased urinary kallikrein excretion and acute rises in plasma renin. 6. In chronic renal hypertensive rats urinary kallikrein excretion was increased only in the animals with two-kidney Goldblatt hypertension. This group was also the only group that demonstrated a significant rise in plasma renin activity.

Isolation of renin granules from rat kidney cortex and evidence for an inactive form of renin (prorenin) in granules and plasma

Renin was demonstrated in particles having a sedimentation velocity similar to that of mitochondria during differential centrifugation separated renin granules from the bulk of mitochondria and lyosomes, as well as from microsomes and cytoplasm. The density of renin granules was 1.202, which differed from the mean equilibrium densities of mitochondria (1.175) and lysosomes (1.170 and 1.230) in the heavy granule fraction. In studies involving gel filtration and polyacrylamide gel electrophoreis, renin granules appeared to contain an inactive form of renin that could be activated by acid treatment, had a higher apparent molecular weight than renin, and may be a more basic molecule. Inactive renin was also studied in plasma by electrophoresis and may originate from renin granules after exocytosis by the juxtaglomerular cells. Inactive renin may be a biosynthetic precursor (prorenin) and may be activated within the cell by a specific protease consequent upon the fusion of renin granules with lysosomes, thus providing a mechanism for the rapid regulation of renin activity prior to secretion.

Radioimmunoassay as an improved method for measurement of serum levels of gentamicin

A radioimmunoassay is described for the measurement of serum concentrations of gentamicin. This radioimmunoassay is more rapid, more specific and more accurate than microbiological assays. Knowledge of serum levels of gentamicin assists the clinician in regulating drug dosage to obtain an optimal therapeutic effect, and yet avoid toxic serum levels.

Renin substrate in granules from rat kidney cortex

1. Subcellular fractions of rat kidney cortex generated angiotensin I continuously over 2h when incubated at 37degreesC with rat renin, indicating the presence of renin substrate within cells in the renal cortex. 2. Renin substrate was located in highest specific concentration in particulate fractions. The particles containing renin substrate had a sedimentation velocity slightly lower than mitochondria and renin granules but greater than the microsomal fraction. 3. Isopycnic gradient centrifugation indicated a density of 1.190g/ml for the particles containing renin substrate, compared with 1.201 for renin granules, 1.177 for mitochondria, and 1.170 and 1.230 for lysosomes in the heavy-granule fraction. 4. In the liver, renin substrate was also found in particles, but these had a lower sedimentation rate than those from the kidney. 5. The molecular weights of renin substrate in kidney and liver granules and rat plasma were similar, namely 61000-62000. 6. On the basis of these biochemical findings, a mechanism for the intrarenal production of angiotensin, incorporating a subcellular reaction scheme, is proposed.

Effect of antihypertensive drugs on the renin-angiotensin system

Renin release from the kidneys is controlled by four major mechanisms - renal baroreceptors, the macula densa, the sympathetic nervous system and other humoral and ionic influences. Recently, the importance of the sympathetic nervous system in modulating renin release for a variety of stimuli has become apparent. The sympathetic adrenergic nerves act on a specific beta-receptor to stimulate renin release from the kidney. Those antihypertensive drugs that inhibit adrenergic nerve transmission tend therefore to lower plasma renin. beta-Adrenoreceptor blocking drugs also generally lower plasma renin by specific inhibition of renal renin release both in animals and humans. Diuretics and vasodilators in contrast elevate plasma renin levels. Plasma renin levels in hypertensive patients are the net result of many diverse influences, and similarly in patients treated with antihypertensive drugs the plasma renin level often is the result of opposing influences. Plasma renin levels tend to return towards normal levels after treatment in hypertensive patients. Plasma renin levels may offer a guide to a more rational basis for antihypertensive therapy in the future. However, the primary aim in treatment of the hypertensive patient should be to lower his blood pressure, independent of the effect of plasma renin levels.

Release of renin from glomeruli isolated from rat kidney

1. Glomeruli free from renal tubules and cell debris were isolated in large numbers from rat kidney cortex by a rapid, simple process of graded sieving on stainless steel meshes. 2. Glomeruli were viable, had fragments of the arterioles attached and contained renin. 3. Glomeruli, when incubated, released renin into the medium. Using a super-fusion technique this was shown to be time dependent until a basal secretion level was achieved. 4. Release of renin was directly proportional to the number of glomeruli and could be stimulated by isoprenaline, adrenaline and noradrenaline in order of the potency of their action on beta-adrenoreceptors. 5. Isolated glomeruli were therefore established as a useful model system for studying the release of renin by direct influences on the juxtaglomerular cells where haemodynamic, tubular and extrarenal influences are removed.

Clearance from the circulation of the rat and whole-body autoradiography in the mouse of 125I-labelled neurophysins

1. The rate of clearance of 125I-labelled porcine neurophysins I and II from the circulation of the rat has an initial fast component followed by a slower component. 2. In the initial phase of clearance the half-life of neurophysin I was 1.50 min (s.e.m. = 0.03) and for neurophysin II was 1.74 min (s.e.m. = 0.05). In the slower phase of clearance the half-life of neurophysin I was 22.6 min (s.e.m. = 2.2) and for neurophysin II was 27.3 min (s.e.m. = 5.8). 3. The first component had a volume of distribution similar to the blood volume and the second component had a volume of distribution similar to the volume of extracellular fuid of the rat. 4. The metabolic clearance rates per 200 g of body weight were 1.94 ml/min (s.e.m. = 0.12) for neurophysin I and 1.29 ml/min (s.e.m. = 0.15) for neurophysin II. 5. Using whole-body autoradiography, the kidney was shown to be the major site of uptake of radioactivity in both virgin female and lactating mice.

The relationship of plasma levels of pindolol in hypertensive patients to effects on blood pressure, plasma renin and plasma noradrenaline levels

1. Fifteen, previously untreated, hypertensive patients were given 20 mg of pindolol, orally. The systolic and diastolic blood pressures fell significantly in 1 h; the effect was maximal 4 h after pindolol, and persisted for at least 8 h. 2. After oral administration of 20 mg of pindolol, its concentration in the plasma reached a peak in 2-3 h. At the end of 8 h, pindolol was not detectable in the plasma. 3. There was a significant relationship between the peak concentration of pindolol in plasma and the maximal change in blood pressure in fifteen previously untreated hypertensive patients. In a separate study of nine-nine hypertensive outpatients taking 15-80 mg of pindolol daily, the blood pressure responses corresponded generally to the concentration of pindolol in plasma 2-3 h after the morning dose. 4. There were no significant changes in plasma renin activity, plasma renin concentration or plasma noradrenaline concentration in the previously untreated patients taking 20 mg of pindolol. There was no relationship between initial plasma renin or noradrenaline levels and blood pressure responses to pindolol. Nor was there any significant relationship between the changes in plasma renin or noradrenaline levels and the changes in blood pressure.

Clearance and metabolism of neurophysins by rat kidney

The half-life in the circulation of 125I-labelled porcine neurophysins, injected intravenously into rats, was determined. The radioactivity in blood collected at intervals after injection was characterized as neurophysin by polyacrylamide gel electrophoresis. The half-life of neurophysin I was 1-5 plus or minus 0-1 (S.E.M.) min and that of neurophusin II was 1-7 plus or minus 0-1 min. The metabolic clearance rate of neurophysin I and neurophysin II was 1-9 plus or minus 0-1 and 1-3 plus or minus 0-2 ml/min/200 g respectively. Clearance from the circulation was due to both equilibration with the extravescular space and rapid specific accumulation by the kidney. The neurophysins were filtered at the glomerulus. Most of the neurophysin takken up by the kidney was incorporated into lysosomes, probably in the proximal tubule and degraded to low-molecular-weight metabolites which appeared in urine and which represented the principle mode of excretion of neurophysins.

Renin measurement in blood collected from the efferent arteriole of the kidney of the rat

Plasma renin could be detected in 16 nl of rat plasma by incubating at 50 degrees C, pH 6.2 with 20 mul of a rat renin substrate. In 60 nl samples it could be estimated and differences in concentration of 20% could be detected. Plasma renin concentration was measured in blood from the superficial efferent arterioles of a rat's kidney. The concentration of renin in different efferent arterioles of the same rat were similar. The renin concentration of efferent arteriolar blood was 361 plus or (-1)89 (S.D.) ng Al ml minus 1 (blood) hour (-1) which was not different from the renin concentration of simultaneously taken femoral artery blood (340 +/- 217). Plasma concentration can be measured in efferent arteriolar blood and will allow the control of renin secretion to be studied.

The renin-angiotensin system in acute renal failure in rats

1. Serial changes in plasma renin activity and plasma angiotensin levels were followed in rats during acute renal failure induced by mercuric chloride or glycerol.

2. During mercuric chloride-induced acute renal failure there were transitory large increases in plasma renin and angiotensin. In contrast, rats with acute renal failure produced by glycerol had a reduction in plasma renin and angiotensin levels at 1 h, after which the levels returned to control values.

3. There was no correlation between the systemic changes in plasma renin and angiotensin and the mortality from or severity of the renal failure.

4. Passive or active immunization of rats to angiotensin afforded no protection against renal failure associated with either glycerol or mercuric chloride.

5. It is concluded that the renin-angiotensin system plays no direct systemic vasoconstrictor role in the production of acute renal failure in these experimental models in rats.

Plasma renin and angiotensin levels in human hypertension following treatment

1. The levels of plasma renin activity or concentration and plasma angiotensin were similar in normotensive subjects and in untreated or treated essential hypertensives.

2. There was a close relationship between plasma renin activity and plasma renin concentration and between these and plasma angiotensin. This suggests that there were no abnormalities in renin substrate or renin kinetics in human essential hypertension.

3. Ganglion blockade did not change the plasma renin levels but α-adrenergic blockade caused a significant rise in plasma catecholamines and plasma renin without change in blood pressure.

4. Both acute and chronic β-adrenergic blockade were associated with a fall in blood pressure and small but significant falls in plasma renin levels.

Plasma renin levels and vascular complications in hypertension

Plasma renin levels, measured in 39 untreated patients in 1967, under conditions of sodium loading and sodium depletion have been related to the incidence of stroke and myocardial infarction. Renin levels were not significantly different in patients with or without vascular complications. Out of 13 patients with persistently low renin levels 6 had suffered either a stroke or a myocardial infarction and 7 had not. Plasma renin levels were also measured in 116 treated hypertensive patients. There was no relation between plasma renin level and vascular complications. It is concluded that levels of plasma renin are not a reliable index of the probability of hypertensive patients suffering a stroke or myocardial infarction.

Subcellular organization of neurophysins, oxytocin, (8-lysine)-vasopressin and adenosine triphosphatase in porcine posterior pituitary lobes

Posterior pituitary lobes from young pigs were fractionated by differential and sucrose-density-gradient centrifugation. The distributions of oxytocin and [8-lysine]-vasopressin were measured by bioassay and the distributions of neurophysin-I and -II by radioimmunoassays specific for each of these two proteins. Most of the hormone and neurophysin applied to the density gradient was localized in particles with the density expected of neurosecretory granules. However, the neurosecretory granules were separated into two bands (D and E). A close statistical correlation between the distributions of [8-lysine]-vasopressin and neurophysin-I, and of oxytocin and neurophysin-II on the gradients, suggested that in vivo porcine neurophysin-I binds [8-lysine]-vasopressin within one population of granules and porcine neurophysin-II binds oxytocin within another type of granule. However, there was no significant separation of oxytocin and vasopressin in fractions D and E. The molar ratios of hormones and neurophysins indicated that there was insufficient of either neurophysin to bind the [8-lysine]-vasopressin in the granule fractions or in the whole gland. Polyacrylamide-gel electrophoresis showed that only bands corresponding in mobility to porcine neurophysins-I, -II and -III were present in large amounts in the whole gland and in the granule fractions. The component with the mobility of neurophysin-III was, however, relatively enriched in whole young glands and granule fractions compared with adult gland extracts. It is suggested that the vasopressin that cannot be assigned to neurophysin-I may occur in (a) vesicles containing vasopressin but no neurophysin, (b) vesicles containing vasopressin and a protein that cannot be quantified by the radioimmunoassays used, such as porcine neurophysin-III, or (c) normal vasopressin-neurophysin granules which have accumulated extra vasopressin. Band E of the gradient was rich in adenosine triphosphatase activity, whereas band D possessed very little of this enzyme.

Renin, angiotensin II, and adrenal corticosteroid relationships during sodium deprivation and angiotensin infusion in normotensive and hypertensive man

The responses of plasma renin activity, plasma angiotensin II, plasma aldosterone, cortisol, and corticosterone to sodium deprivation and to angiotensin II infusion (100 ng/min) were measured in 8 normotensive patients and in 17 patients with essential hypertension. Following sodium deprivations, plasma renin activity rose from 0.513 ± 0.100 to 1.029 ± 0.124 ng/ml hour -1 in normotensive patients and from 0.406 ± 0.077 to 0.629 ± 0.059 ng/ml hour -1 in hypertensive patients. Plasma angiotensin II did not parallel changes in plasma renin activity: in normotensive patients plasma angiotensin II was unchanged by sodium deprivation (31.8 ± 6.0 compared with 30.1 ± 4.6 pg/ml), but in hypertensive patients it rose from 22.2 ± 3.4 to 36.4 ± 5.1 pg/ml. Plasma aldosterone rose equally in both groups following sodium deprivation (5.8 ± 1.3 to 15.3 ± 2.4 ng/100 ml for normotensive patients and 5.9 ± 1.4 to 14.4 ± 1.6 ng/100 ml for hypertensive patients) and angiotensin infusion (5.8 ± 1.3 to 10.4 ± 2.1 ng/100 ml in sodium-loaded normotensive patients, 15.3 ± 2.4 to 19.6 ± 3.6 ng/100 ml in sodium-deprived normotensive patients, 5.9 ± 1.4 to 11.4 ± 2.7 ng/100 ml in sodium-loaded hypertensive patients, and 14.4 ± 1.6 to 22.2 ± 2.6 ng/100 ml in sodium-deprived hypertensive patients). However, changes in endogenous plasma angiotensin II did not correlate with the rise in plasma aldosterone caused by sodium deprivation, and, despite much larger increases in plasma angiotensin II during angiotensin II infusion, plasma aldosterone showed smaller rises than those accompanying sodium deprivation. Plasma renin activity fell during angiotensin II infusion, in both groups of patients during both sodium loading and sodium deprivation, and, hence, the infusion constitutes a potent feedback inhibition of renin release in normotensive and hypertensive man. Plasma cortisol and corticosterone were unaltered by sodium deprivation but fell significantly with the angiotensin II infusion.

Radioimmunoassay for plasma antidiuretic hormone

Antibodies to [8-lysine]-vasopressin (LVP) were produced in rabbits by a macrophage harvesting technique. Using these antibodies a radioimmunoassay for vasopressin was established using LVP as standard and for labelling with 125I. The antibody demonstrated complete cross-reactivity to [8-arginine]- and [8-ornithine]-vasopressin but concentrations of oxytocin 1000 times greater caused no displacement. A simple extraction procedure for antidiuretic hormone (ADH) in plasma is described. Employing this extraction procedure followed by radioimmunoassay, plasma levels of ADH were measured in sheep. The mean level of plasma ADH in nine sheep was found to be 5·28 ± 1·18 in arterial blood and this rose to 21·04 ± 7·29 μu./ml after haemorrhage of 10 to 20% of their blood volume.

Clonidine in the treatment of hypertension

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A radiochemical renin assay

1. A synthetic 3-([(14)C]valine)-labelled tetradecapeptide renin substrate was used to measure renin concentration. Renin liberated (14)C-labelled angiotensin I, which was separated from the labelled substrate by paper chromatography. The conversion of substrate into angiotensin I was quantitated by liquid-scintillation counting of radioactivity. 2. The rate of conversion of the substrate into angiotensin I was shown to be linearly related to renin concentration and time under suitable conditions. Angiotensin generation measured in this system agrees well with that measured by bioassay. 3. It is suggested that the use of a pure substrate offers advantages that include the standardization of current units of renin measurement.

Plasma renin in chronic experimental heart failure and during renal sodium "escape" from mineralocorticoids

A striking increase in the plasma renin level occurred in dogs with low output right heart failure secondary to tricuspid insufficiency and pulmonic stenosis and in three of five animals with high output failure produced by a large arteriovenous fistula. When dogs with a small arteriovenous fistula were given daily injections of DOCA, the renal sodium "escape" phenomenon occurred. In these animals, the level of plasma renin was suppressed during DOCA administration both during the initial period of sodium retention and also later when sodium balance was normal or negative. In contrast, when dogs with a larger arteriovenous fistula but without evidence of cardiac failure were given DOCA, they retained sodium and developed signs of congestive heart failure. However, in these animals with congestion and ascites, in contrast to the dogs that developed spontaneous high output failure, the plasma renin was low. Renin-substrate was unaltered in all of the experimental situations studied except for the decrease observed in dogs with low output right heart failure. In these animals, it seems likely that decreased renin-substrate was secondary to hepatic congestion and liver damage. The renin-angiotensin system does not seem to be related to the "escape" phenomenon, and renin does not appear to be the factor that makes the kidney unusually responsive to mineralocorticoids. Thus, in experimental heart failure the renin-angiotensin system was activated, but in the congestive syndrome produced by DOCA the plasma renin level was suppressed.

Cross-circulation experiments on the mechanism of the natriuresis during saline loading in the dog

Cross-circulation through normal recipient dogs of blood from saline-loaded donor dogs that had escaped from desoxycorticosterone acetate (DCA) resulted in a sixfold rise in renal sodium excretion in the recipients. The change occurred without a detectable alteration in filtered sodium (F Na ). To investigate the locus of secretion of a humoral factor responsible for the natriuresis, a series of ablational procedures was performed in DCA-escaped, saline-loaded donors. Nephrectomy, hepatectomy, or decapitation before saline loading and cross-circulation failed to block the increase in renal sodium excretion in the recipients. Analysis of periods during cross-circulation with a decrease in F Na lower than the lowest control value showed that sodium excretion was elevated significantly above control levels in experiments with normal, hepatectomized, and decapitated donors. In contrast, with nephrectomized donors the increase in sodium excretion in the recipients was negligible. This finding points to the need for further study of the kidney as a possible source of a humoral factor in the control of renal salt excretion.

Relation of plasma renin to sodium balance and arterial pressure in experimental renal hypertension

Measurements of plasma renin were made in unilaterally nephrectomized dogs with renal artery stenosis and hypertension. Plasma renin was elevated throughout the course of the malignant renal hypertensive disease, and during the first three days only in chronic hypertension. Hypertension was produced by renal artery constriction in unilaterally nephrectomized dogs with prior thoracic caval constriction and in sodium-depleted, left nephrectomized animals. Plasma renin was high in both dogs with caval constriction and sodium depletion before hypertension was added. When the renal artery was constricted, two of the dogs with thoracic caval constriction developed malignant hypertension and a further striking increase in plasma renin occurred. In two other dogs with caval constriction, chronic hypertension developed but plasma renin increased further in only one of the two animals; this occurred during the first four days of hypertension after which plasma renin returned to the high control level. The sodium-depleted dogs developed chronic hypertension following renal artery constriction but no further elevation in plasma renin occurred. Sodium repletion and sodium depletion of chronic hypertensive dogs produced marked changes in plasma renin without alterations in arterial pressure. The present findings revealed a striking correlation between plasma renin and sodium balance but neither bore any relation to the level of arterial pressure.