The renin-angiotensin system (first of two parts)

Role of the renin-angiotensin system in the systemic vasoconstriction of chronic congestive heart failure

In 15 patients with severe chronic left ventricular failure, plasma renin activity (PRA) ranged widely, from 0.2--39 ng/ml/hr. The level of PRA was unrelated to cardiac output (CO) or pulmonary artery wedge pressure (PWP), but was slightly negatively correlated with mean arterial pressure (MAP) (r = -0.45) and systemic vascular resistance (SVR) (r = -0.40). After infusion of the angiotensin converting enzyme inhibitor teprotide (SQ 20,881) PWP fell from 26.3 +/- 1.3 (SEM) to 20.3 +/- 1.4 mm Hg (P less than 0.001), CO rose from 3.94 +/- 0.23 to 4.75 +/- 0.31 l/min (P less than 0.001), MAP fell from 87.5 +/- 3.8 to 77.9 +/- 4.1 mm Hg (P less than 0.001) and SVR from 1619 +/- 148 to 1252 +/- 137 dyne-sec-cm-5 (P less than 0.001). The fall in MAP and in SVR was significantly correlated with control PRA (r = 0.68 and r = 0.58, respectively). When subjects were divided on the basis of control PRA the hemodynamic response to teprotide was greatest in the high renin group. PRA rose after teprotide (8.7 +/- 3.4 to 37.9 +/- 7.7 ng/ml/hr, P less than 0.05) but plasma norepinephrine fell (619.1 +/- 103.6 to 449.7 +/- 75.7, P less than 0.05). The renin-angiotensin system thus appears to have an important role in the elevated SVR in some patients with heart failure. Chronic inhibition of converting enzyme should be explored as a possible therapeutic approach.

Renin-like (angiotensinogenase) activity in human eccrine sweat

The presence of renin or renin-like activity (RLA) was demonstrated in human eccrine sweat incubated with purified sheep angiotensinogen, using rat bioassay and angiotensin I radioimmunoassay. Following cholinergic stimulation, sweat RLA was found to range between 0 (unmeasurable) and 266 ng/ml.h, i.e. RLA-values of sweat can be about 10 times higher than those of plasma. Therefore, renin synthesis in sweat glands could be assumed. RLA following activation of beta-adrenergic receptors by the administration of isoprenaline (Aludrin) did not exceed the mean values obtained by cholinergic activation. After beta-adrenergic receptor blockade by propranolol (Dociton), RLA became unmeasurably low. Higher RLA-values were found after local injection of dibutyryl-c-AMP (90--210 ng/ml.h). The results indicate a beta-adrenergic regulation of RLA-release in human sweat glands. Human sweat glands appear to be useful for studying extrarenal renin release.

Renin and blood-pressure in children with renal scarring and vesicoureteric reflux

Plasma-renin-activity (P.R.A.) was raised in 9 of 15 hypertensive children with pyelonephritic scarring secondary to urinary-tract infection and vesicoureteric reflux and also in 8 of 100 normotensive children with such scars. P.R.A. was much less likely to fall with age in normotensive children with renal scarring than in normal children. The identification of hyperreninaemic normotensive children with renal scarring is important, since P.R.A. may prove to be of value in early identification of children at risk of developing hypertension. A longitudinal follow-up is proposed to establish this hypothesis.

Plasma and urinary aldosterone and their interrelations with blood pressure, plasma renin activity and urinary electrolytes in normotensive subjects

Plasma aldosterone (PA), urinary aldosterone excretion (Aldo-U), urinary sodium and potassium excretion and supine and sitting blood pressure (BP) were studied in 120 normotensive subjects. PA was determined after 1 h supine rest (basal PA), after ambulation for 3--4 h (upright PA) and after stimulation with 80 mg frusemide orally (stimulated PA). Aldo-U and urinary electrolytes were measured the day before the PA determinations. PA and Aldo-U were determined by specific radioimmunoassays. Basal PA rose approximately two-fold after upright posture and about three-fold after frusemide stimulation. However, there was a very wide scatter in PA values between individual subjects. A significant correlation existed between basal PA and Aldo-U (r = 0.42), P less than 0.001). Aldo-U decreased with increasing age. The PA values correlated fairly well with the concomitant values for plasma renin activity (r = 0.26--0.40, P less than 0.004 for basal PRA and P less than 0.001) for both upright and stimulated PRA). No relationships could be found between Aldo-U and urinary electrolyte excretions. No correlations were observed between aldosterone and BP.

Systemic hypertension after surgical treatment of a congenital arteriovenous malformation

The development of systemic hypertension, in an eight-year-old girl, after resection of a large arteriovenous malformation, is described. The hypertension was related to an elevated plasma renin activity and was controlled with propranolol. A possible mechanism for the rise in plasma renin activity is postulated.

Purification and partial characterization of rat brain acid proteinase (isorenin)

1. Isorenin was purified 2000-fold from rat brain by a simple 3-step procedure involving affinity chromatography on pepstatinyl-Sepharose, The preparation appears as a homogenous protein in analytical polyacrylamide gel electrophoresis. Sodium dodecyl sulfate gel electrophoresis indicated an apparent molecular weight of 45 000. Isoelectric focusing separated isoenzymes with isoelectric points at pH 5.45, 5.87, 6.16 and 7.05. 2. The enzyme generates antiotensin I from tetradecapeptide (pH optimum 4.7) and from sheep angiotensinogen (pH optima 3.9 and 5.5). The rate of angiotensin I formation from tetradecapeptide was 30 000 times higher than that from sheep angiotensinogen. The enzyme has acid protease activity at pH 3.2 with hemoglobin as the substrate and pepstatin is a potent inhibitor of the enzyme with a Ki of less than 10(-9) M. 3. The properties of the enzyme strongly suggest that it is identical with cathepsin D.

Arteriolar nephrosclerosis in the Syrian hamster

Syrian hamsters developed spontaneous renal lesions that resembled those of arteriolar nephrosclerosis in man, and differed from other spontaneously occurring or virus-induced renal diseases in other rodent species. Morphologic changes were mainly degenerative with little cellular exudation and were associated with histologic changes in the intrarenal vasculature. The renal lesions were progressive, often fatal and sometimes were complicated by glomerular amyloidosis with the nephrotic syndrome and uremia. Endstage kidneys often had fibrinoid necrosis of intrarenal arterioles and thus resembled lesions characteristic of the malignant phase of human essential hypertension. Fibrinoid necrosis of small arterioles was common in the uterus, ovaries or testes of affected animals; it was less frequent in mesenteric or coronary vessels. Cardiac thrombosis, often involving the left atrium or left atrioventricular valves, also was common. Changes occurred earlier and often were more severe in females than in males. This disease was a major cause of morbidity and mortality and hampered life-span studies.

Humoral and neurohormonal aspects of blood pressure regulation: focus on angiotensin

Angiotensin circulates in the blood as a hormone. Its main target organs are vascular smooth muscle, adrenal gland and the kidney. Hormonal angiotensin increases blood pressure by its vasoconstrictor action, by stimulation of aldosterone secretion and subsequent sodium and water retention, and by the stimulation of catecholamine release. Circulating plasma angiotensin also effects brain mechanisms of blood pressure regulation. In addition to this hormonal function, angiotensin is present in the brain as part of an endogenous brain renin-angiotensin system. Brain angiotensin is not secreted into the blood and can be considered a neurohormone with local function. A role of brain angiotensin in the maintenance of high blood pressure of spontaneously hypertensive rats has been demonstrated. Circulating plasma angiotensin appears to influence brain renin levels and vice versa. Stimulation of specific areas in the brain known to be involved in the regulation of the cardiovascular system, stimulate renin secretion from the kidney. The renin-angiotensin system can therefore serve as an example for the intimate interrelationship between humoral and neurohumoral mechanisms of blood pressure regulation.

Renin-like (angiotensinogenase) activity in sweat of patients with cystic fibrosis and controls

Using bioassay method (rat blood pressure technique) as well as the radioimmunoassay, renin-like activity (RLA) was measured in eccrine sweat of patients with cystic fibrosis of the pancreas (CF) and of controls. Sweat-formation was induced by pilocarpine-iontophoresis or by local injection of carbamylcholine (Doryl). RLA-values between O (not measurable) and 460 ng/ml.h were measured. With increasing sweat flow-rate a tendency to lower RLA-values was detected. No significant difference was observed between CF and controls. From the observation that RLA of sweat is up to 30 times higher than that of plasma, it is concluded that RLA is probably released not from plasma but from the sweat glands themselves, where it is stored or synthesized.

Volume-dependent parameters in essential hypertension

Blood pressure, renal blood flow, total blood volume (TBV), plasma renin activity, and vascular reactivities to angiotensin and norepinephrine were studied in 48 normotensive subjects and 106 essential, sustained, hypertensive patients with normal renal function, balanced sodium intake, and urinary output. A significant negative pressure-volume relationship was observed in normal subjects. Among the hypertensive patients, some were inside the 95% confidence limits of the normal curve and the others were above, indicating a disturbance in the pressure-volume relationship. A quantitative evaluation of the pressure-volume disturbance was proposed and discussed. The blood pressure of each hypertensive patient corresponded to two different blood volume values: the renal valve and the theoretical value extrapolated from the normal curve. The difference between the two values was called deltaTBV and was positive in hypertensive patients. The deltaTBV value was negatively correlated with the renal blood flow, the creatinine clearance, the plasma renin activity, and the vascular reactivities to angiotensin and norepinephrine (P less than 0.0001). The parameters were not correlated with the real blood volume. This study demonstrates quantitatively a pressure-volume disturbance in essential hypertension. This disturbance is strongly correlated with the renal function and the renin-angiotensin system changes.

Distribution of angiotensin II receptors in rat brain

Angiotensin II binding activity of rat brain particles was examined using [125I]-angiotensin II (0.1-0.3 nM) in the presence and absence of excess unlabelled angiotensin II. Certain features of the binding suggested that physiological receptors were involved. The binding activity was temperature dependent and was increased 3-fold by the addition of 0.5 M EDTA. The binding appeared specific as judged by inhibition with angiotensin II agonists and antagonists. The "specific" binding was saturable, two-thirds reversible and occurred with high affinity. The equilibrium dissociation constant (Kd) of the "specific" binding was 0.9 nM. Subcellular fractionation studies indicated that over 90% of the binding was associated with particulate matter and was concentrated in the crude microsomal fraction. Binding was localized to the midbrain, thalamus, septum, hypothalamus and medulla; Very low levels of binding were found in the cortex, hippocampus and striatum; The lateral septum had the highest binding activity of all the tissues examined. Subdivision of the medulla showed that the highest binding activity was associated with the area postrema and medullary regions ventral to this organ.

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.

Plasma renin activity following central infusion of angiotensin II and altered CSF sodium concentration in the conscious goat

To study central influences on the renal release of renin, angiotensin II was infused into the lateral cerebral ventricle of conscious hydrated goats. CSF sodium concentrations was increased or lowered by similar infusions of hypertonic NaCl or of isotonic fructose solution. Infusion of angiotensin II in doses from 0.5 to 1 mug caused a drop in plasma renin activity (PRA) and elicited a rise in blood pressure, antidiuresis, natriuresis, and thirst. Intraventricular infusion of hypertonic NaCl also supressed PRA, induced antidiuresis, natriuresis, and an inconsistent rise in blood pressure. Lowering of CSF [Na+] by infusion of isotonic fructose caused a rise in PRA and was followed by a water diuresis in the non-hydrated animal. The fructose infusions caused some decrease in renal K+ excretion but no consistent change in renal Na+ excretion. The results indicate that angiotensin II and changes in sodium balance modulate renal renin release also via the central nervous system.

Stimulation of renin secretion by various methods: optional results with hydrochlorothiazide

Serum renin concentration (SRC) was determined in 97 hypertensive patients under basal conditions and during stimulation of renin secretion. Renin secretion was stimulated by upright posture and by either of the following means: (a) diet containing 20 mEq Na/24 hours for 3 days; (b) 300 mg i.v. diazoxide injections; (c) oral ingestion of 80 mg furosemide; (d) oral hydrochlorothiazide (HCT), 25 mg twice daily for 3 days. HCT was used in 6 patients previously treated with daizoxide and in 8 patients previously treated with furosemide. Using pairs of basal and stimulated SRC determinations, the patients could be classified as high, normal, or low renin hypertensives. HCT proved to be the most convenient stimulus as far as efficacy, reliability and the patients' tolerance were concerned, and compared well with sodium restriction.

Plasma renin activity during exercise in the dog

Previous workers have suggested that a rise in plasma renin activity (PRA) may mediate some of the hemodynamic changes associated with exercise. To test this hypothesis in nine dogs chronically instrumented for measurement of aortic pressure (catheter) or cardiac output (ascending aorta electromagnetic flow probe) PRA was measured by radioimmunoassay in blood samples drawn before and during running on a level treadmill at 4-8 miles per hour. Exercise caused increases in heart rate from 96 +/- 5 (SE) to 186 +/- 7 beats/min, cardiac output from 2.8 +/- 0.3 to 6.2 +/- 0.6 liters/min, and mean aortic pressure from 115 +/- 5 to 132 +/- 5 mm Hg (P less than 0.01). Mean PRA was 6.6 +/- 0.7 (SE) ng of angiotensin 1/ml per 3 hours before and 7.6 +/- 1.2 ng Ang I during exercise, values that are not different statistically. Propranolol reduced PRA at rest from 8.6 +/- 1.1 to 5.9 +/- 1.1 ng Ang 1 (P less than 0.05), but there was no significant difference between resting and exercise levels, although the increments in heart rate, cardiac output, and mean aortic pressure were reduced. Standing on hindlimbs for 5 minutes did not cause a change in mean aortic pressure or PRA. However, administration of pentolinium reduced mean aortic pressure, and PRA rose from 6.0 +/- 1.1 to 9.8 +/- 1.5 ng Ang I. Exercise, with or without beta-adrenergic blockade, does not cause increased PRA in conscious dogs in which the renin-angiotensin system is normally responsive.

Different antihypertensive effect of beta-blocking drugs in low and normal-high renin hypertension

The treatment response to beta-adrenoceptor blocking drugs was compared in two groups of patients with primary (essential) hypertension and different renin levels. Each group consisted of 25 patients and was equally distributed regarding age, severity and stage of hypertension. In the first group (group 1), the mean upright plasma renin activity was 0.8 ng ml-1h-1 (range 0.3 to 1.5) and the patients were considered to have low renin hypertension. In the other group (group 2) the patients had a mean plasma renin activity of 2.1 ng ml-1h-1 (range 1.1 to 5.1) and were considered to have normal to high renin hypertension. In both groups the patients were initially treated with beta-blocking drugs; in group 1 with a beta-blocker corresponding to an average dose of 311 mg propranolol a day for at least eight weeks and in group 2 with propranolol 320 mg a day in a fixed dose for eight weeks. The hypotensive response differed significantly between the two groups (p less than 0.001). In group 1 the pretreatment blood pressure was 197/117 mm Hg supine and 198/120 mm Hg standing. During treatment blood pressure decreased only 5/3 mm Hg supine and 9/5 mm Hg standing. The pretreatment blood pressure in group 2 was 187/114 mm Hg supine and 186/117 mm Hg standing. Beta-blocking therapy reduced blood pressure 36/23 and 34/18 mm Hg, respectively (both p less than 0.001). Pulse rates fell significantly in the two groups, both in the lying and standing positions. In 17 patients with low renin hypertension (group 1), a volume-depleting drug was added (spironolactone, 14 patients; thiazides, 3 patients) and this achieved a marked fall in blood pressure levels of 38/16 mm Hg supine and 37/19 mm Hg standing (both p less than 0.001). These results suggest the following: (1) Most patients with normal to high plasma renin activity respond well to moderate doses of propranolol. (2) Propranolol given in the same doses is almost without antihypertensive effect in patients with low renin hypertension. (3) A volume factor may be operating in patients with low renin hypertension since a hypotensive effect is demonstrated after the addition of volume-depleting drugs. (4) Determination of plasma renin activity with adequate methods can predict the treatment response to hypotensive agents.

Big renin: identification, chemical properties and clinical implications

Big renin has a greater molecular weight (63,000 versus 43,000) than normal renin, but it shares the characteristic enzymatic and immunologic properties of normal renin. As it exists in the kidney or plasma of a patient, big renin is less active than normal renin, but its enzymatic activity is greatly enhanced by exposure to pH values of 3.0 to 3.6 or by brief incubation with pepsin or trypsin. Use of the terms prorenin and zymogen might be withheld until big renin is shown to exist in normal tissue or plasma and to be converted to normal renin in vivo. To date, big renin has been found in renal tumors and other abnormal kidney tissues as well as in the plasma of patients with renal disorders. The remarkable activation of big renin at pH levels of 3.3 can be used to detect its presence. If a method involving acidification is used to quantitate plasma renin activity of a patient with circulating big renin, the activated plasma renin activity greatly exceeds that measured in plasma maintained at neutral pH. Gel filtration of plasma is used to prove the presence of big renin. When large amounts of big renin are secreted by a renal tumor, hyperfusion may ensue and be cured by removal of the tumor. The secretion of small amounts of big renin does not necessarily result in any physiologic disorder. However, if there is a concomitant diminution or absence of normal renin a state of apparent hyporeninemia exists, as we have observed in diabetic nephropathy; this may be associated with hypoaldosteronism and hyperkalemia. Big renin does not appear to respond to physiologic changes that stimulate or suppress normal plasma renin activity. The finding of big renin may indicate the presence of certain renin-secreting renal tumors or other renal disorders, especially diabetic nephropathy.

Controlled treatment of primary hypertension with propranolol and spironolactone. A crossover study with special reference to initial plasma renin activity

Twenty-seven patients with hypertension were randomly allocated to a 10 month crossover study. Treatment consisted of spironolactone (200 mg/day for 2 months), propranolol (320 mg/day for 2 months) and combined administration of both drugs at half the dosage. Between treatment periods placebo was given for 2 months. Fourteen patients were previously untreated. The average pretreatment blood pressure for the entire group was 188/114 +/- 16/7(mean +/- standard deviation) mm Hg supine and 188/118 +/- 20/9 mm Hg standing. Both spironolactone and propranolol reduced blood pressure significantly in both the supine and standing positions. Upright plasma renin activity was determined by radioimmunoassay of angiotensin I. The average initial level was 1.9 +/- 1.2 (range 0.4 to 5.0) ng/ml/hr. There was a close correlation between plasma renin activity and the effects of the drugs: With increasing renin level the response to propranolol was better whereas the opposite was true for spironolactone. The combination of spironolactone and propranolol decreased the blood pressure still further in the supine and standing positions, irrespective of initial plasma renin activity. All patients achieved a normal supine pressure. Blood pressure and plasma renin activity returned toward pretreatment values during placebo administration. It is concluded that pretreatment levels of plasma renin activity can predict the antihypertensive response to propranolol and spironolactone. The combination of the two drugs, which have different modes of action, will effectively reduce blood pressure in hypertension. The results support the concept that the renin-angiotensin-aldo-sterone system may be involved in primary hypertension.

Hypertension in terminal renal failure

Inverse interrelations between plasma renin activity and exchangeable sodium or blood volume were found in both normotensive (N = 23) and hypertensive (N =29) hemodialysis patients (r= 0.47; P less than 0.005); however, mean plasma renin for any given sodium/volume state was at least two-fold higher in hypertensive than in normotensive hemodialysis patients or normal subjects (N =31). In the hemodialysis patients, blood pressure correlated weakly but significantly with the products of circulating renin and exchangeable sodium (r=0.37; P less than 0.005) or blood volume (r = 0.29; P less than 0.05). Multiple regression analysis including duration of previous hypertension as the second independent variable increased these correlation coefficients to 0.44 and 0.42, respectively. This suggests that hypertension in endstage kidney disease is often associated with resetting of the body sodium/fluid=renin feedback mechanism. Inappropriately increased plasma renine activity relative to the body sodium/volume state as well as high blood pressure-induced vascular changes may play important complementary roles, but it appears evident that additional mechanisms are also operative in maintaining end-stage renal hypertension.

Pathologic hypofunction of the renin-angiotensin-aldosterone system

The literature now contains reports of many cases of aldosterone deficiency. Usually, the presenting features are persistent hyperkalemia and tendencies to serious urinary sodium loss and hypotension. A classification of defects leading to pathologic hypofunction of the renin-angiotensin-aldosterone system (RAAS hypofunction) is presented, with emphasis on idiopathic hyporeninemia (probably the most common). Criteria for diagnosis are (1) normal adrenal glucocorticoid function, (2) low aldosterone excretion under basal and stimulated conditions, and (3) renal tubular responsiveness to exogenous mineralocorticoid. The condition is effectively managed with mineralocorticoid replacement therapy and should be considered in the presence of unexplained persistent hyperkalemia, hyponatremia, or postural hypotension.

Renin concentrations and effects of propranolol and spironolactone in patients with hypertension

In a crossover study 32 patients with hypertension were randomly allocated to treatment with spironolactone 200 mg/day for two months, propranolol 320 mg/day for two months, and a combination of both drugs at half the dose. Between the treatments placebo was given for two months. Both spironolactone and propranolol lowered the blood pressure significantly in both positions. The initial plasma renin activity (PRA) levels ranged from 0-4 to 5-0 mug angiotensin I l-1 h-1, and there was a close correlation between these levels and the effects of the drugs: with increasing PRA the response to propranolol was better while the opposite was true for spironolactone. Spironolactone reduced the blood pressure more at eight than at four weeks, while no such difference could be shown for propranolol. Spironolactone and propranolol together decreased the blood pressure still further irrespective of the initial PRA. All patients achieved a normal supine blood pressure.

Unimpeded plasma renin increase after intravenous furosemide during saline replacement

The effect on plasma renin activity of intravenous furosemide combined with saline replacement of the volume depletion was studied in twelve patients with insignificant heart disease. In ten of the patients the investigation was repeated without saline replacement. It was found that saline infusion, reducing or eliminating hemoconcentration, had no significant influence on the marked plasma renin increase. In eight of the patients the combined furosemide-saline study was performed during right-hear catheterization. Decrease in atrial pressures, known to occur within 15 min after furosemide intravenously, was virtually absent with the saline replacement. It is concluded that plasma volume reduction after intravenous furosemide is responsible for decreased filling pressures of the ventricles but not for plasma renin increase.

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.

Renal blood flow and its response to angiotensin II. An interaction between oral contraceptive agents, sodium intake, and the renin-angiotensin system in healthy young women

A variety of estrogen- and progestin-containing oral contraceptive agents reduced renal blood flow (RBF) significantly in 23 healthy, nonhypertensive young women, to a mean of 75 +/- 3.3% of the value expected for their age and dietary sodium intake (P less than 0.001). There was also significant activation of the renin-angiotensin system: renin substrate was increased approximately 3-fold in association with a striking increase in the circulating renin activity and angiotensin II levels in relation to sodium intake and excretion. Two observations suggest that the RBF reduction was directly mediated by angiotensin II. A correlation was demonstrable between circulating angiotensin II and RBF (P less than 0.01), and renal vascular responsiveness to angiotensin II infused into the renal artery was reduced significantly (P less than 0.001). Moreover, the oral contraceptive agents modified the basic relationship between sodium balance and vascular responsiveness to angiotensin II, suggesting that the agents acted through some mechanism other than alteration in the state of sodium balance. These observations provide further evidence for an important role of angiotensin II as a determinant of RBF. Renal vasoconstriction may contribute to the genesis of a number of complications, such as sodium retention and hypertension, associated with oral contraceptive use.

Hemodynamic lesions in hypertension

Essential hypertension is increasingly recognized as a nonhomogenous disorder by various methods of study. The hemodynamic approach, coupled with clinical determination of the range and lability of blood pressure, has resulted in the description of several subgroups: labile hypertension with normal or elevated cardiac output, fixed or established hypertension with varying cardiac output and advanced hypertension with normal or low cardiac output. There is a tendency to postulate that these categories are stages of one disorder, but this remains to be proved. Still other patients have been described who may be further set off by exceptionally labile or hyperkinetic features. In some hypertensive patients, the peripheral resistance is normal; however, regardless of its numerical value, it is now considered to be increased if it fails to decrease normally in the presence of elevated cardiac output. Because an elevated cardiac output is the hemodynamic function that differentiates these groups, and renovascular hypertension as well, it is the focus of much current work. New interest in the central blood volume, the peripheral veins, and the portal veins and splanchnic circulation is focused on their connection with cardiac out-put. Newly appreciated, too, is the existence of parasympathetic inhibition in hypertension, which not only contributes to elevations of heart rate, cardiac output and possibly renin secretion, but also depresses baroreflex responses. Thus far, hemodynamic and endocrine mechanisms of hypertension have not been studied together, except possibly through the blood volume, which remains a highly controversial topic. In this paper, some recent work in the above areas is reviewed and emphasis is given to studies in man.

Direct effect of beta-adrenergic stimulation on renin release by the rat kidney slice in vitro

Controversy exists regarding the mechanism by which catecholamines stimulate renin secretion in vivo. A sensitive rat kidney slice system was utilized to study the direct effects of adrenergic agonists and antagonists on renin release in vitro. Catecholamines were protected from degradation by the addition of ascorbic acid to the incubation medium. Significant dose-related stimulation of renin release was observed with epinephrine and norepinephrine in concentrations from 1.5 times 10(-9) to 1.5 times 10(-7)M and with isoproterenol in concentrations from 2 times 10(-9) to 2 times 10(-7)M. No significant stimulation was seen with 10(-10)M concentrations of the three agents. Methoxamine (10(-6)M) stimulated renin release significantly (P less than 0.01). The stimulation observed with epinephrine, norepinephrine, or isoproterenol was blocked by d,l- and l-propranolol (2 times 10(-4)M) but not by d-ropranolol (2 times 10(-4)M) or phentolamine (9 times 10(-4)M). Methoxamine-induced stimulation was abolished by d,l-propranolol but not by phentolamine. These data that the in vitro kidney slice system is responsive to physiological concentrations of catecholamines when they are protected from degradation. The results further demonstrate a direct stimulatory role for beta-adrenergic agents on renin release and suggest that alpha-adrenergic effects seen in vivo are mediated indirectly by hemodynamic, vascular, or functional changes 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.

The reliability of the measurement of plasma renin activity by radioimmunoassay

A radioimmunoassay of angiotensin I has been applied to the measurement of plasma renin activity. Angiotensin I was generated in plasma samples by 3 h incubation at 37 degrees C and pH 5.6 after addition of EDTA and Dowex. The generated amount of angiotensin I was measured by radioimmunoassay in the eluate of the Dowex column. With this method a negligible amount of angiotensin I was measured after incubation at 4 degrees C (0.8 ng/ml per 3 h). Eluate of blank plasma had no measurable effect on the standard curve. The mean recovery of angiotensin I was 87%. The limit of detection of the assay was 0.5 ng/ml per 3 h. The results obtained using different antisera were equal. A marked variation was found in immunological properties of different standard preparations of angiotensin I tested. The mean value of angiotensin I generation per Goldblatt Unit (G.U.) renin was 3.9 with 10-4 ng/h. In normotensive control subjects, the plasma renin concentration, whileon unrestricted diet and after 3 h of ambulation, was on average 0.39 with 10-minus 4 G.U./ml, range 0.12 with 10-minus 4-0.91 with 10-minus 4. With the use of the same plasma extracts for radioimmunoassay and bioassay, a perfect correlation was found between the plasma renin activities measured with both assays. The differences found between the results of both assays could be fully explained by the different biological activities of the standards used (Angiotensin I, Schwarz Mann, and Angiotensin II, Ciba-Geigy). With a direct radioimmunoassay, angiotensin I was generated in plasma by 3 h incubation at 37 degrees C and pH 5.6 after addition of phenylmethanesulfonyl fluoride, 8-hydroxyquinoline and 2,3-dimercaptopropanol (dimercaprol). The generated amount of angiotensin I was measured by the above mentioned radioimmunoassay. A fairish correlation was found between the generated amounts of angiotensin I measured in the Dowex eluate and those found in the incubated plasma. Especially in the lowest range, lower values were obtained by the latter assay. However, the generated amounts of angiotensin I measured in non-incubated plasma samples (3 h at 4 degrees C) was on average 6.4 ng/ml per 3 h and accounted for 748% of the amounts found after incubation at 37 degrees C.