The control of renin release

The epidemiology and pathophysiology of heart failure

Heart failure (HF) remains a major growing public health problem in the United States. Despite extensive understanding of the mechanism at the molecular level and innovations in therapy, HF carries high morbidity and mortality rates, with frequent hospital admissions. In the Medicare population, HF is the leading cause for hospitalization, accounting for more than1 million admissions per year. The authors provide a review of the epidemiology and pathophysiology of HF.

Afferent mechanisms of sodium retention in cirrhosis and hepatorenal syndrome

Cirrhosis induces extra-cellular fluid volume expansion, which when the disease is advanced can be severe and poorly responsive to therapy. Prevention and/or effective therapy for cirrhotic edema requires understanding the stimulus that initiates and maintains sodium retention. Despite much study, this stimulus remains unknown. Work over the last several years has shown that signals originating in the liver can influence a variety of systemic functions, including extra-cellular fluid volume control. We review work on the afferent mechanisms triggering sodium retention in cirrhosis and suggest that the data are most consistent with the existence of a sensor in the hepatic circulation that contributes to normal extra-cellular fluid volume control (that is, a 'volume' sensor) and that in cirrhosis, the sensor is pathologically activated by the hepatic circulatory abnormalities caused by the disease. Detailed analysis of the hepatic circulation in normal conditions and cirrhosis is needed.

Bartter's syndrome without hyperplasia of the juxtaglomerular apparatus, treated with indomethacin

The present report describes a case of potassium-wasting nephropathy with the physiological and endocrinological findings that are typical for Bartter's syndrome (BS). However, the renal juxtaglomerular apparatus showed no hyperplasia at two renal biopsies two years apart. The short-term (9 days) effect of indomethacin in combination with spironolactone was a suppression of hyperreninemia and hyperaldosteronism and an increase in vascular sensitivity to angiotensin II associated with potassium and sodium retention. Subsequently, on indomethacin alone, potassium balance was obtained on a lower level with persistent hypokalemia and persistent renal potassium leakage. Hypokalemia persisted during long-term (9 months) treatment with indomethacin despite normalization of the activity of the renin-aldosterone system. The results indicate that indomethacin as long-term treatment may be ineffective in maintaining a normal potassium balance in BS.

Partial correction of hypertension by angiotensin II blockade in a patient with phaeochromocytoma

This case report describes a patient with malignant hypertension and phaeochromocytoma in whom blockade of angiotensin II receptors by the competitive antagonist 1-sar-8-ala-angiotensin II (Saralasin) resulted in a partial correction of the elevated BP. Plasma renin activity was high and rose further during the blockade. Competitive inhibition of angiotensin II by Saralasin does not abolish the pressor effect of catecholamines. It was therefore interesting to observe that in this patient with phaeochromocytoma, independently, both alpha-adrenergic receptor blockade and angiotensin II receptor blockade were effective in lowering BP.

Plasma renin activity and hypertensive organ manifestations in 50-year-old males

From a screening examination in a randomly selected third of the 50-year-old male population in Göteborg, Sweden, a 10% subsample was selected as a reference group (n=80). All untreated persons with SBP greater than 175 or DBP greater than 115 mmHg on two separate occasions made up the hypertension group (n=35). The reference group and the hypertension group were subjected to the same investigations, including BP measurement before and after rest and determination of plasma renin activity (PRA), urinary sodium and norepinephrine excretion and GFR. Plasma renin activity was approximately normally distributed in both the reference and the hypertension group. Mean values were 0.78 +/- 0.18 and 0.65 +/- 0.17 ng/ml/h respectively, the difference being almost statistically significant (0.10 greater than p greater than 0.05). There was no difference with respect to sodium excretion between the reference group and the hypertension group. In the reference group, heart rate was positively correlated to PRA and to urinary norepinephrine excretion during the day. No linear correlation between PAR and BP was found, either in the reference group, or in the hypertension group. Sodium excretion during the day was positively correlated to GFR in the hypertension group, but not in the reference group. Compared to hypertensives with normal or high sodium excretion during the day, the hypertensives with low sodium excretion during the day were characterized by a higher BP, a lower GFR and a reversed diurnal rhythm of urine excretion. Thus, low sodium excretion seemed to indicate more severe hypertension with increased renal resistance during the day. The hypertension group was also divided with regard to sodium excretion into a low, normal and high renin group. The low renin group had the lowest GFR and with rising renin group (from low via normal to high) there was a significant increase in GFR and a significant decrease in resting BP. The results indicate that low renin hypertension is not a more mild, but indeed rather a more severe form of hypertension.

Role of the kidney in congestive heart failure

The changes in renal function observed in congestive heart failure include altered pressures and flows and increased reabsorption of sodium and water leading to expanded extracellular fluid volume. These renal effects are mediated by a variety of volume and pressure sensors that stimulate various effectors which act on the kidney. The role of these sensors and effectors, the relationship between left ventricular function (LVF) and urinary sodium excretion (UNaV) and the role of angiotensin II in mediating the renal hemodynamic changes are reviewed. Rats with experimentally induced myocardial infarction (MI) were studied 3 weeks after infarction. Although UNaV decreased as LVF worsened, the decrease in UNaV was evident even in rats with MI and minimal LVF impairment. Infusion of teprotide (an inhibitor of angiotensin I converting enzyme) returned the hemodynamic parameters to or toward values seen in rats without MI, thereby documenting an important role for angiotensin II in congestive heart failure.

Effect of Lifelong High- or Low-Salt Intake on Blood Pressure, Left Ventricular Mass and Plasma Insulin in Wistar Rats

BACKGROUND

Salt restriction is recommended for hypertension treatment to reduce blood pressure, but its effect on some risk factors is still a matter of discussion. The aim of this study was to observe the effect of a long period of salt restriction or overload on blood pressure, left ventricular mass (LVM), kidney mass (KM), glucose tolerance, and plasma insulin.

METHODS

Male Wistar rats were fed from weaning with a low-salt diet (LSD) or a high-salt diet (HSD) until 72 weeks of age. After 48 weeks, the diets were changed in half of the rats: HSD until 48 weeks and then LSD (LHSD) and LSD until 48 weeks and then HSD (HLSD). Body weight, blood pressure, electrolyte excretion, creatinine clearance, plasma renin activity, LVM, KM, and intravenous glucose tolerance test with insulin determinations were evaluated.

RESULTS

Blood pressure, LVM and KM were higher on the HSD than on the LSD. Blood pressure was lower on the LHSD than on the HLSD. There were no differences in LVM and KM on the LHSD compared with the HLSD. The relationship between area under the curve (AUC) of insulin and glucose during the intravenous glucose tolerance test was higher on the LSD. No differences were detected in AUC between the two groups of rats whose diet were inverted with 48 weeks of age.

CONCLUSIONS

A chronic HSD increases blood pressure, LVM, and KM and a chronic LSD increases plasma insulin in response to a glucose challenge in aging rats. The hypotensive effect of salt restriction is not modified by a previous long period on a HSD.

Opposing glucose set points hypothesis of essential hypertension

Understanding of the mechanisms involved in the development of essential hypertension is incomplete. Many studies have demonstrated that sympathetic overactivity is involved in the development of essential hypertension. In addition, hypertensive patients, as a group, are insulin resistant. The relationship of increased sympathetic activity to insulin resistance in essential hypertension has not been adequately explained. Hypertensive subjects have been reported to have rapid gastric emptying compared to control subjects. They also have increased postprandial hypotensive responses to high carbohydrate meals compared with non-hypertensive control subjects. The author hypothesizes that essential hypertension is the result of a metabolic disregulation in which the body's glucose regulatory system splits into two separate glucose control systems with two different homeostatic set points for fasting and postprandial glucose levels. It is proposed that insulin is the principle regulator of the lower glucose set point while counter-regulatory hormones, predominantly catecholamines, as well as the rate of gastric emptying, are regulators of the upper glucose set point. The tension between these two opposing control systems results in increased sympathetic activity, increased fasting and postprandial glucose and insulin levels and an increased rate of gastric emptying in hypertension. It is hypothesized that increased sympathetic activity from these opposing regulatory systems initiates a vicious cycle that eventually leads to the development of essential hypertension. This hypothesis explains the beneficial effects of agents that either slow carbohydrate absorption or delay gastric emptying on essential hypertension and postprandial hypotension. New therapeutic strategies for treatment of hypertension are suggested by this hypothesis.

Failure of angiotensin II to suppress plasma renin activity in normotensive subjects with a positive family history of hypertension

The renin-angiotensin system is implicated in the pathophysiology of hypertension. Renin release is regulated by a number of factors, including circulating Ang II (angiotensin II), the so-called short feedback loop. The aim of the present study was to investigate the responsiveness of circulating Ang II on PRA (plasma renin activity) in normotensive subjects with a PFH or NFH (positive or negative family history of hypertension respectively). PRA, renal haemodynamics and urinary sodium excretion were measured during infusion of Ang II without and with pretreatment with the AT1 (Ang II type 1) receptor blocker irbesartan. Normotensive men with a PFH (n=13) and NFH (n=10), with a mean age of 38 years, were given on different occasions intravenous Ang II infusions of 0.1, 0.5 and 1.0 ng.kg-1 of body weight.min-1 before and after pretreatment with 150 mg of irbesartan once a day for 5 consecutive days. RPF (renal plasma flow) and GFR (glomerular filtration rate) were also measured. Before Ang II infusion, the PFH and NFH groups did not differ with respect to BP (blood pressure), body mass index, PRA, RBF (renal blood flow) or urinary sodium. There was no difference in BP or renal haemodynamic response to the highest Ang II dose between the groups. PRA declined with the highest Ang II dose (P<0.01) in subjects with a NFH, but not in subjects with a PFH. After treatment with irbesartan when Ang II had no effect on BP in either group, Ang II also suppressed PRA in subjects with a PFH (P<0.01), and the difference between the groups at baseline was thus eliminated. In conclusion, these findings indicate that subjects with a PFH have a defective Ang II suppression of PRA, which is corrected by AT1 receptor blockade.

Combination therapy with ACE inhibitors/angiotensin II receptor antagonists and diuretics in hypertension

Essential hypertension is a very heterogeneous disease and different pressor mechanisms might interact to increase blood pressure. It is therefore not surprising that antihypertensive drugs, given as monotherapy, normalize blood pressure in only a fraction of hypertensive patients. This is, for instance, the case for diuretics, angiotensin converting enzyme (ACE) inhibitors and angiotensin II (AT1) receptor antagonists administered as single agents. The rationale for combining antihypertensive agents relates in part to the concept that the blood pressure-lowering effect may be enhanced when two classes are coadministered. Also, combination therapy serves to counteract counter-regulatory mechanisms that are triggered whenever pharmacologic intervention is initiated and that act to limit the efficacy of the antihypertensive medication. For example, the compensatory rise in renin secretion induced by sodium depletion may become the predominant factor sustaining high blood pressure. Simultaneous blockade of the renin-angiotensin system, with either an ACE inhibitor or an AT1-receptor blocker, makes this compensatory hyper-reninemia ineffective and allows maximum benefit from sodium depletion. The combination of a blocker of the renin-angiotensin system and a low dose of a diuretic increases the effectiveness, but not at the expense of tolerability compared with the individual components administered alone. Fixed-dose combinations containing an ACE inhibitor or an AT1-receptor blocker and a diuretic are therefore likely to become increasingly used not only as second-line therapy but also as first-line treatment.

Renal hemodynamic and hormonal responses to the angiotensin II antagonist candesartan

The development of very specific blockers for the angiotensin II type 1 (AT(1)) receptor made it possible to examine the contribution of angiotensin II to normal control mechanisms and disease with a specificity beyond what ACE inhibitors could provide. In the present study, we explored the contribution of angiotensin II to 2 renal mechanisms: renal hemodynamics and the short feedback loop, in which angiotensin II acts as a determinant of renin release. To make that comparison, we studied healthy volunteers in balance on a 10-mmol sodium intake to activate the renin system. Our goal was to compare the relation between the dose of candesartan, an AT(1) receptor blocker, and the renal hemodynamic and hormonal responses. A second goal was to ascertain the relation between time after candesartan administration and the peak response. Twelve healthy subjects (mean age 33+/-2.3 years) in low-sodium balance were administered candesartan in 4-, 8-, 16-, and 32-mg doses. Candesartan produced a dose-related increase in renal plasma flow, with the maximum vasodilator response at 16 mg (142+/-13 mL. min(-1). 1.73 m(-2)) occurring during the first 4 hours after the dose. Likewise, candesartan caused a dose-related rise in plasma renin activity, with 32 mg as the dose producing the greatest response at 4 and 24 hours after administration. The peak plasma renin activity achieved in this study (15.3+/-1.6 ng. L(-1). s(-1); 55.0+/-5.6 ng angiotensin I. mL(-1). h(-1)) was found at the 4- to 8-hour interval after dosing in a subset of subjects (n=5) who received the 16-mg dose 4 hours earlier than the other subjects. On the basis of the difference in the relation between dose and response and the relationship between time after drug administration and response, the determinants of the renal hemodynamic and hormonal response can be said to differ. The remarkable rise in plasma renin activity after candesartan is substantially larger than that in earlier studies with ACE inhibition, providing additional evidence for non-ACE-dependent angiotensin II generation in the kidney.

Treatment of edematous disorders with diuretics

Generalized edema results from alterations in renal sodium homeostasis that ultimately result in an expansion of extracellular fluid volume and accumulation of interstitial fluid. The common edematous disorders include congestive heart failure, cirrhosis, nephrotic syndrome, and renal insufficiency. The abnormalities of sodium homeostasis contributing to edema formation in each condition are discussed. Management of volume homeostasis, with an emphasis on the role of diuretic therapy, is reviewed.

Predicting short-term outcome in severely ill heart failure patients: implications regarding listing for urgent cardiac transplantation and patient selection for temporary ventricular assist device support

BACKGROUND

The purpose of this study was to determine which patients on a cardiac transplantation list required a ventricular assist device.

METHODS AND RESULTS

In a preliminary study, 26 patients with decompensated severe New York Heart Association class IV chronic heart failure were studied. Blood levels for sodium, hemoglobin, cytokines, neurohormones, and hemodynamics were obtained. During short-term follow-up of 40 days, 12 patients had undergone emergent implantation of a ventricular assist device (range 1-27 days, mean 5 days), 4 died (range 14-38 days, mean 26 days), and 5 were alive and receiving only medical therapy while waiting for a transplantation. In addition, five patients had undergone transplantation (range 5-29 days, mean 18 days, excluded from further analysis). Survival curves were constructed by comparing the incidence of death and the implantation of an emergent ventricular assist device in patients with values of a variable above or below the mean value (or median for nonnormally distributed data). There was a significantly greater incidence of death or need for a ventricular assist device in patients with higher levels of tumor necrosis factor-alpha (P = .008), lower levels of serum sodium and hemoglobin (P = .02 and P = .03, respectively), higher heart rates (P = .03), and higher plasma norepinephrine levels (P = .01). The Cox proportional hazards model demonstrated that only serum sodium (P = .03) independently predicted those patients who died or who required emergent left ventricular assist device.

CONCLUSION

Numerous variables, particularly serum sodium, need to be considered when evaluating which patients on the transplant list require early assist device implantation or urgent transplantation. These preliminary observations merit confirmation in a larger patient population.

Role of angiotensin in the congenital anomalies of the kidney and urinary tract in the mouse and the human

The role of angiotensin in fluid and electrolyte and blood pressure homeostasis is well known. Recent developments indicate that angiotensin has a profound role not only in the developing urinary tract but also in the response of the urinary tract to specific noxious stimuli. Furthermore, the role of angiotensin II and its receptor has been understood quite poorly with respect to the developing renal unit. Knockout mice for the ATR2 gene show a significant incidence of congenital urinary tract anomalies. The congenital anomalies of the kidney and urinary tract (CAKUT) seen in these mice are very similar to the anomalies observed in humans. This has been supported further by the finding of an abnormality in the genetic sequence in patients with CAKUT. This article reviews experimental laboratory data as well as the potential implications for humans.

Current concepts in renovascular hypertension

Renovascular disease represents an important dimension of hypertension. Although estimates vary regarding the exact prevalence of renovascular hypertension, it is being diagnosed with increasing frequency because of refined criteria for the workup and the availability of sensitive diagnostic tests. Two major pathologic entities--atherosclerosis and fibromuscular dysplasia--account for most cases of renovascular hypertension. Once the diagnosis and clinical significance of renal artery stenosis in a hypertensive patient are established, appropriate and specific therapy should be considered. The goal is not only to treat hypertension, but to preserve and restore renal function. Although antihypertensive drug therapy may lower the blood pressure, reperfusion of the kidney (surgical, angioplasty) is a desirable long-term objective in the management of patients with renovascular hypertension. With careful selection of therapeutic choices, we are now able to render optimal care to patients with renovascular hypertension.

Prazosin's effect in high renin hypertension complicating pheochromocytoma

During three consecutive days of prazosin treatment in a patient with pheochromocytoma, urinary catecholamine metabolite levels were correlated with plasma renin activity. Suppression of renin plasma activity resulted in sustained hemodynamic and clinical improvement, while no remarkable changes were observed in urinary catecholamine metabolite levels. This suggests that prazosin may interrupt the vicious cycle of worsening hypertension provoked by further activation of the renin-angiotensin system mediated by excessive circulating catecholamines.

Plasma renin activity and urinary kallikrein excretion in response to intravenous furosemide in diabetic patients

The responsiveness of renin-angiotensin and kallikrein-kinin systems to furosemide challenge has been investigated in forty-six diabetic patients (34 NIDDM/12 IDDM), subdivided into Group I (uncomplicated DM), Group II (DM with hypertension), Group III (DM with nephropathy), Group IV (DM with hypertension and nephropathy) and a control group of 10 healthy volunteers. Plasma renin activity (PRA) was estimated by radioimmunoassay in blood samples drawn before and 10 min after furosemide administration (0.5 mg/kg i.v.). Urinary kallikrein levels were measured by bioassay using estrogenized rat uterus preparation in 4h urine samples collected before and after the diuretic. Urinary Na+ and K+ were also measured. The basal PRA in diabetics was not significantly different from controls, whereas, urinary kallikrein levels were markedly low in all patients. Both PRA and kallikrein levels increased after furosemide in controls while in diabetics this response was severely blunted. In a subset of Group I, a paradoxical fall in PRA and kallikrein levels was noted after furosemide, an effect similar to that observed in patients with nephropathy (Group III). This response in absence of clinical and biochemical parameters of nephropathy indicates early derangement of renal hemodynamic mechanisms heralding the onset of nephropathy.

Role of macula densa in diuretics-induced renin release

Diuretic therapy may enhance renin release by various mechanisms, principally contraction of extracellular fluid volume and its effects, including a fall in arterial pressure. Awake hydropenic or volume-expanded rats received diuretics (amiloride and hydrochlorothiazide) that are known inhibitors of NaCl transport beyond the macula densa; also the well-known Na(+)-K(+)-2 Cl- transport system inhibitor furosemide was administered. We also evaluated the effect of a dose of ethacrynic acid (a drug that shares the same mechanism of action as furosemide but is not diuretic in the rat). The direct action of the diuretics on renin-producing cells was examined in isolated glomeruli; a rise in renin release was observed with the calmodulin inhibitor trifluoperazine (10(-5) M). Renin release in intact hydropenic rats was not altered by diuretic therapy, but furosemide increased plasma renin activity in hydropenic as well as in volume-expanded rats. This demonstrates the importance of furosemide inhibition of transport in the macula densa for its renin secretory action. None of the diuretics (amiloride, hydrochlorothiazide, ethacrynic acid, or furosemide) elicited changes in renin release from glomeruli (10(-6) to 10(-3) M); amiloride and hydrochlorothiazide (10(-4) to 10(-3) M) did not change renin release from slices, but 10(-3) M ethacrynic acid and furosemide increased renin secretion in this preparation. This suggests that an effect on the macula densa is essential in loop diuretic-mediated renin release.(ABSTRACT TRUNCATED AT 250 WORDS)

Body composition, normal electrolyte concentrations, and the maintenance of normal volume, tonicity, and acid-base metabolism

Because the internal environment of the body is largely a fluid medium, the preservation of the volume and composition of the body fluids is absolutely vital to circulatory status and the extraordinarily complicated functions of the human body. The fluid compartments do not exist as fixed spaces with identical compositions but rather are in constant interchange with each other and have strikingly different compositions. Methods of movement of solutes and water include diffusion along electrochemical gradients, by hydrostatic pressure, osmotic forces, bulk flow, primary and secondary active transport, capillary blood flow, and oncotic pressure. Complex feedback control mechanisms exist to ensure homeostasis or equilibrium and include participation by the kidneys, lungs, gastrointestinal tract, the circulatory system, the endocrine system, and the CNS. The maintenance of extracellular volume is centered around the control of balance of the sodium salts. Multiple afferent (or sensing) and efferent (or effector) mechanisms exist to accomplish this homeostasis. The most important determinants of the osmolality or tonicity of the body fluids is the excretion or retention of water by the kidney, thirst mechanisms, and the intake of water. The serum sodium concentration is the laboratory test most often used clinically to assess tonicity. The pH of the body fluids and the major acid-base buffer systems are also carefully regulated. The lungs are responsible for the elimination of the carbon dioxide produced by cellular metabolism, and the kidneys excrete hydrogen ions and regulate the concentration of bicarbonate in the body fluids. Urinary net acid excretion, the hydrogen ions excreted as titratable acid and ammonium ions minus any bicarbonate, equals the acid added to the ECF from the diet and metabolism plus any fecal losses of alkali.

Influence of crying on plasma renin activity and aldosterone concentration

Infants and toddlers often start crying at venopuncture and the stress of crying has been known to increase the levels of plasma renin activity (PRA) and plasma aldosterone concentration (PAC), but no precise information is available. We measured the levels of PRA and PAC in blood samples taken from 30 infants and toddlers within 1 min after the onset of crying, as induced by venopuncture, and 3 and 5 min after continuation of crying (PRA1.0, PRA3.0, PRA5.0, and PAC1.0, PAC3.0, PAC5.0). The age of these subjects ranged from 1 to 30 months (median 16 months). PRA1.0, PRA3.0 and PRA5.0 were 4.0 +/- 1.8 ng/ml per hour, 5.5 +/- 2.7 ng/ml per hour, and 7.8 +/- 4.2 ng/ml per hour, respectively. PAC1.0, PAC3.0 and PAC5.0 were 210 +/- 110 pg/ml, 231 +/- 118 pg/ml and 269 +/- 145 pg/ml, respectively. Both PRA and PAC increased with elapsing time. The increase in PRA was marked after a short episode of crying, but that in PAC was of a mild degree.

Angiotensin-converting enzyme inhibitors in heart failure

Recognition of the importance of the renin-angiotension-aldosterone system in heart failure, along with an appreciation of the hemodynamic benefits of vasodilator therapy has led to the widespread use of angiotensin-converting enzyme (ACE) inhibitors in the treatment of heart failure. The ACE inhibitors are the only class of vasodilator agents shown to have a significant protective effect against mortality in patients with heart failure.

Renin regulation in type II diabetes mellitus: influence of dietary sodium

Numerous abnormalities in the renin-angiotensin system have been described in diabetes mellitus. Plasma renin activity (PRA) has been noted to be low, normal, and high in diabetic patients; these variable results may be explained by differences in patient selection and standardization of study conditions. We evaluated PRA and inactive renin responses in Type II normotensive (n = 7) and hypertensive (n = 12) diabetic patients specifically selected for no or minimal evidence (background retinopathy) for microvascular complications. Patients were studied in a metabolic ward after 7 days on a constant low sodium (20 meq/day) and 7 days on a high sodium (250 meq/day) diet. Nondiabetic control subjects (n = 7) were evaluated under similar conditions. On low sodium intake, mean PRA levels were significantly reduced in the hypertensive diabetic group, but were not different between the control and normotensive diabetic groups. Hypertensive diabetic patients on high sodium intake also had greater reductions in PRA responses compared with the other study groups. In general, diabetic subjects on high sodium intake excreted less sodium and had more cumulative sodium retention than control subjects. Levels of inactive renin were not significantly different between the normotensive and hypertensive diabetic patients and were comparable with the levels in control subjects. Inactive renin levels changed in a similar direction and magnitude as PRA in response to sodium intake and posture in the three study groups. Infusion of angiotensin II led to comparable reductions in PRA in both diabetic groups and in the control group, suggesting an intact short feedback loop control.(ABSTRACT TRUNCATED AT 250 WORDS)

Prostaglandins in congestive heart failure and the effects of nonsteroidal anti-inflammatory drugs

With the failure of the heart as a pump, there ensues a series of neurohumoral compensations that defend organ perfusion at the expense of alterations in cardiac filling pressures and the distribution of blood flow to various regional circulations. Activation of the sympathetic nervous system and the renin-angiotensin II-aldosterone system and increases in circulating arginine vasopressin maintain arterial blood pressure by producing systemic arteriolar vasoconstriction and the renal retention of salt and water. Constriction of the efferent arterioles in the kidney by angiotensin II and norepinephrine promotes reabsorption of glomerular filtrate in the peritubular capillaries and maintains glomerular filtration in the face of declines in glomerular plasma flow and the glomerular permeability-surface area ultrafiltration coefficient. In resting, sodium-replete, conscious animals and humans, pharmacologic inhibition of renal cyclo-oxygenase by nonsteroidal anti-inflammatory drugs has little or no effect on renal hemodynamics. However, electrical or reflex stimulation of the renal nerves, intrarenal infusion of angiotensin II, or infusion of arginine vasopressin stimulates the release of vasodilator prostaglandins from the kidneys. In sodium-depleted animals or humans, and when cardiac output decreases, there is an increase in total peripheral vascular resistance but little change in renal vascular resistance. Increased renal synthesis of vasodilator prostaglandins (presumably by the blood vessels) maintains renal blood flow despite increased release of renin and norepinephrine from the kidneys. In these situations, pharmacologic inhibition of renal cyclo-oxygenase is accompanied by marked reductions in renal blood flow and glomerular filtration rate. When this occurs in patients with advanced heart failure, reversible oliguric renal failure may result. In this setting, cyclo-oxygenase inhibition may also increase arterial pressure and induce additional depression of cardiac function. Recent data indicate that blood vessels have the capacity to synthesize the sulfidopeptide leukotrienes C4, D4, and E4, which can constrict peripheral and renal blood vessels and alter vascular permeability. The vascular cell types responsible for leukotriene C4 synthesis and the potential roles of these vasoactive eicosanoids in kidney and other regional circulations are currently under study.

Humoral effects of long-term oral enalapril therapy

Twenty-seven subjects with essential hypertension were prospectively followed for a minimum of 100 weeks, receiving either enalapril monotherapy or enalapril and hydrochlorothiazide combination therapy. Blood pressure and the renin-angiotensin-aldosterone system were assessed following 4 weeks of placebo therapy, and 56 and 96 weeks of maintenance drug therapy. Blood pressure was well controlled with either form of therapy. Plasma renin activity remained stimulated following both long-term monotherapy and combination therapy. However, immunoreactive plasma angiotensin II concentration was not suppressed following either long-term monotherapy or combination therapy. Similarly, plasma aldosterone concentration was not suppressed following either form of therapy; indeed, combination therapy was associated with stimulation of plasma aldosterone concentration. We conclude that enalapril monotherapy or enalapril/hydrochlorothiazide therapy was effective in controlling blood pressure, but that long-term blood pressure control must be related to an angiotensin II independent antihypertensive mechanism.

Mechanism of intestinal adaptation in rats with acute renal failure

Acute renal failure (ARF) was experimentally induced in rats and the specific activity of mucosal Na-K-ATPase activity in segments of the small intestine and colon was measured. Bilateral nephrectomy (BN) resulted in a significant evaluation of the enzyme activity in all segments examined. With an additional procedure of adrenalectomy (BN + Ax), the enzyme activity failed to show any increase in ARF rats produced by BN. However, a supplementation of a maintenance dose of dexamethasone to adrenalectomized ARF rats (BN + Ax + DM 10) resulted in a significant resumption of the activity in all intestinal segments, although its increase was insignificant in the duodenum. Addition of a high dose of DOCA (BN + Ax + DOCA 500) was effective in increasing the enzyme activity only in the colon but not in the small intestine. With a high dose of DM or a maintenance dose of DM plus a high dose of DOCA (BN + Ax + DM 30 or BN + Ax + DM 10 + DOCA 500), there was an increase in the enzyme activity of all intestinal segments. In ARF rats induced by bilateral lower ureteral ligation (BLUL), the enzyme activity did not show any increase at all. Addition of a high dose of DOCA to this animal model (BLUL + DOCA 500) brought about the increase of the enzyme activity in the intestinal segments but for the jejunum.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute effects of cold on blood pressure, renin-angiotensin-aldosterone system, catecholamines and adrenal steroids in man

In an attempt to study effects of cold on blood pressure and the renin-angiotensin-aldosterone system, 34 healthy young subjects with or without a family history of essential hypertension were exposed to moderate cold (4 degrees C for 1 h) or severe cold (immersion of the hands to 0 degrees C for 10 min). Moderate cold elevated blood pressure, aldosterone, cortisol and noradrenaline when the subjects wore summer clothing but not when the subjects wore winter clothing. Regardless of the clothing worn, skin blood flow and plasma renin activity decreased significantly in response to moderate cold but angiotensin II decreased insignificantly. Severe cold elevated blood pressure, cortisol, aldosterone and noradrenaline. Administration of dexamethasone significantly depressed an increase of aldosterone and cortisol in response to cold but failed to effect an elevation of blood pressure and noradrenaline. Plasma renin activity and angiotensin II concentration were not affected at all during and after cold exposure. It is suggested that, among the various hormones studied, noradrenaline is the only hormone responsible for an elevation of blood pressure in response to cold.

Pathophysiology of essential hypertension. Role of the autonomic nervous system

The participation of the autonomic nervous system in hypertension is not restricted to increased cardiac action and peripheral vasoconstriction during periods of stress. The three major systems that are particularly involved in hypertension, the heart, brain, and kidneys, are interrelated in a multifaceted way by which all of them inform, interfere, and influence one another. The autonomic nervous system will play an important role in most types of hypertension whether these are volume-dependent, cardiogenically mediated, or related to stimulation of the renin-angiotensin system.

Cardiovascular, humoral, and renal effects of phenoxybenzamine in hypertension

We examined the effects of alpha adrenergic receptor blockade with phenoxybenzamine on various parameters related to blood pressure regulation in 10 normotensive and 12 essential hypertensive subjects. The responses were observed before and after phenoxybenzamine treatment during standardized maneuvers of volume expansion with saline infusion and volume contraction with a diuretic. Alpha adrenergic blockade produced a significantly greater (P less than 0.02) reduction in blood pressure in the hypertensive group than in the normotensive subjects. The baroreceptor response, evaluated by comparing the change in plasma norepinephrine concentration in relation to the change in blood pressure, was significantly reduced (P less than 0.05) in hypertensives compared to normal subjects. Plasma and urinary norepinephrine concentration, which were similar in the two groups, increased in both during phenoxybenzamine treatment. There was no significant change in the mean levels of plasma renin activity or plasma aldosterone concentration in either group after phenoxybenzamine treatment. However, the relationship between plasma renin activity and plasma aldosterone levels, as judged by linear regression analysis, was significantly altered (P less than 0.05) by phenoxybenzamine therapy in both groups. The latter may reflect an effect of phenoxybenzamine on the metabolism or secretion of aldosterone. These results, utilizing an alpha adrenergic antagonist, confirm the enhanced vascular reactivity and diminished baroreceptor function in essential hypertension; no evidence for an alpha adrenergic effect on plasma renin activity could be demonstrated in normotensive or hypertensive subjects.

Antihypertensive mechanism of diuretic treatment with chlorthalidone. Complementary roles of sympathetic axis and sodium

Twenty-three patients with untreated mild to moderate essential hypertension had on the average an abnormally increased cardiovascular pressor responsiveness to exogenous norepinephrine (NE), while plasma and urinary NE, exchangeable body sodium and blood volume were normal. An increased pressor responsiveness to angiotensin II in these patients was associated with a tendency for low plasma renin activity (PRA). Compared to placebo conditions, treatment with chlorthalidone, 100 mg/day, for 6 weeks significantly decreased blood pressure and exchangeable sodium in these hypertensive patients but not in ten normal subjects; blood volume and heart rate were unchanged in both groups. Chlorthalidone induced a marked increase in PRA, but only a mild increase in angiotensin II pressor dose. In contrast, the diuretic caused a greater increase in NE pressor dose than in plasma NE in the hypertensive group, thus improving the disturbed relationship between plasma NE and NE responsiveness in these patients. No significant modification of plasma NE and NE responsiveness occurred in diuretic-treated normal subjects. In addition to sodium and the renin-angiotensin system, the sympathetic regulatory axis seems to be involved in the antihypertensive mechanism of chlorthalidone. Thiazide-like diuretics may decrease blood pressure in essential hypertension in part by lowering an abnormally high cardiovascular NE responsiveness without causing an equivalent increase in circulating NE.

The clinical application of converting enzyme inhibitors

Chronic blockade of the renin angiotensin system became possible when orally active inhibitors of angiotensin converting enzyme, the enzyme which catalyzes the transformation of angiotensin I into angiotensin II, were synthetized. Two compounds, captopril and enalapril, have been investigated in clinical studies. The decrease of the pressor response to exogenous angiotensin I and of the circulating levels of angiotensin II following administration of these inhibitors has been demonstrated to be directly related to the degree of suppression of plasma angiotensin converting enzyme activity. These inhibitors have been shown to normalize blood pressure alone in some hypertensive patients whereas in many others, satisfactory blood pressure control can be achieved only after the addition of a diuretic. Captopril and enalapril also markedly improve cardiac function of patients with chronic congestive heart failure. Chronic blockade of the renin angiotensin system has therefore provided an interesting new approach to the treatment of clinical hypertension and heart failure.

Acute effects of prizidilol on blood pressure, heart rate, catecholamines, renin and aldosterone in essential hypertension

Prizidilol is a new antihypertensive agent reported to possess combined precapillary vasodilator and betareceptor-blocking properties. To clarify the profile of the acute effects of prizidilol in man, a variable dose study was performed in 8 patients with benign essential hypertension. Blood pressure, heart rate, plasma renin activity, aldosterone, plasma and urinary catecholamines and electrolytes were determined at short intervals before and up to 23 h after oral administration of placebo and prizidilol 150, 300 and 600 mg. The 4 studies were performed at weekly intervals according to a Latin square design. Prizidilol produced dose-dependent decreases in supine and upright blood pressure, with an initial change after about 2 h and maximal effects from 4 to 8 h after drug ingestion. Following a high dose of prizidilol, supine mean blood pressure (average 128 mmHg prior to treatment) was normalised (less than 107 mmHg) from 3 to 7 h and was still below predose level 23 h after ingestion. The only reported side effects were postural dizziness in 2 cases (corresponding to a fall in systolic upright blood pressure to less than 95 mmHg) and headache in one case. A biphasic variation in heart rate and plasma renin activity, with an early drop and a subsequent tendency to a slight rise, was observed after an intermediate or high dose of prizidilol. Plasma norepinephrine levels were increased by a high dose of prizidilol, while plasma epinephrine, aldosterone and plasma and urinary electrolytes were not consistently changed. Prizidilol in a a single oral dose appeared to be a potent antihypertensive agent. The profile of heart rate and plasma renin point to early dominance of beta-blockade followed by appearance of the concomitant vasodilator properties of prizidiol.

Long-term control of congestive heart failure with captopril

The long-term effects of captopril therapy were assessed by sequential hemodynamic studies over a 6 month period in 19 patients with resistant congestive heart failure. Initial improvement during the first week of therapy was noted only in 11 and was marked by significant (p less than 0.005) increases in cardiac output and stroke volume, slowing of heart rate, and reduction of total peripheral resistance. Of the remaining eight patients, seven improved subsequently with maintained therapy so that by the end of 3 months of treatment only one patient failed to respond significantly. The hemodynamic index that reflected response most consistently was the shortening in pulmonary mean transit time. Simultaneously with clinical improvement there was a reduction in cardiopulmonary volume that reflected a reduction in pulmonary congestion and probably systemic vasodilation. Associated with these hemodynamic changes there was an increase in plasma renin activity and a significant reduction in plasma aldosterone, but these changes did not differ significantly between patients who responded markedly and those who responded moderately to converting enzyme inhibition. These results suggest that the response of congestive heart failure to captopril can occur gradually. Improvement was related to peripheral hemodynamic changes which led to a reduction in both total peripheral resistance and cardiopulmonary volume. The reduction in the plasma aldosterone/renin activity ratio was an effective marker of compliance.

Response of the renin-angiotensin-aldosterone system to upright tilting and to intravenous frusemide: effect of prior metoprolol and propranolol

1 Upright tilting in normal volunteers caused increases in plasma active and total renin, angiotensin II and aldosterone; a slight but significant fall in inactive renin accompanied these changes. 2 The alterations in the renin-angiotensin-aldosterone system on tilting took up to 1 h upright to become fully established. 3 Large intravenous doses of propranolol or metoprolol attenuated, without abolishing, the rises in active renin, angiotensin II, and aldosterone; the attenuation was most evident soon after tilting and was largely overcome by 1 h upright. Inactive renin did not fall significantly after beta-adrenoceptor blockade. 4 Intravenous frusemide caused immediate rises in plasma active, total and inactive renin, angiotensin II, and aldosterone, which then declined over 2 h despite increasing cumulative sodium losses. 5 Intravenous propranolol or metoprolol attenuated, without abolishing, these early increases in the components of the renin-angiotensin-aldosterone system after frusemide. 6 Prior oral metoprolol or propranolol, while significantly slowing the heart, did not limit the early rise in plasma angiotensin II following intravenous frusemide. 7 Thus in contrast to previous workers, we did not find that propranolol eliminated the response of the renin-angiotensin system to upright tilting; in part this difference appeared to be due to the longer tilt we employed. 8 Also in contrast to earlier work, we found attenuation by both intravenous propranolol and metoprolol of the immediate rise in renin after intravenous frusemide.

Body fluid homeostasis in congestive heart failure and cirrhosis with ascites

The urinary excretion of salt and water in man is regulated by a variety of renal and extrarenal mechanisms that respond to changes in dietary sodium intake as well as to alterations in the holding capacity of the vascular and interstitial compartments. Changes in extracellular fluid volume are detected by volume sensors located in the intrathoracic vascular bed, the kidney and other organs. These sensing mechanisms gauge the adequacy of intravascular volume relative to capacitance at various sites within the circulation. Congestive heart failure and cirrhosis with ascites are two disease states of man in which a hemodynamic disturbance within a given circulatory subcompartment is perceived by these sensing mechanisms and results in renal sodium retention. While the primary disturbance in both of these conditions originates outside the kidney, a variety of renal effector mechanisms respond to the perceived circulatory disturbance and result in enhanced tubule reabsorption of salt and water. These effector mechanisms involve physical adjustments in renal microvascular hemodynamics, tubule fluid composition and flow rate and transtubular ion gradients. These in turn are partially regulated by a variety of neural and humoral pathways including the renin-angiotensin-aldosterone axis, prostaglandins, and kinins.

Sustained haemodynamic and clinical effects of captopril in long-term treatment of severe chronic congestive heart failure

1 The angiotensin-converting-enzyme inhibitor captopril is known to produce beneficial haemodynamic effects in patients with chronic congestive heart failure. 2 Twelve patients with chronic congestive heart failure were conventionally treated with digitalis and diuretic therapy plus oral captopril (75-150 mg/day), and 14 patients were used as a control group. 3 There was no improvement in functional and haemodynamic values in the controls, but the patients treated with captopril showed a significant functional improvement (increase of exercise time and improvement in New York Heart Association functional class), a definitive decrease in systemic vascular resistance (20%), and a significant increase in the cardiac index and ejection fraction (18% and 28% respectively).

Hormonal pattern during development of hypertension in spontaneously hypertensive rats (SHR)

Urinary excretion of sodium, noradrenaline, dopamine, aldosterone, prostaglandin E2 and plasma renin activity were determined in 7 and 16 weeks old spontaneously hypertensive rats (SHR) and in two normotensive control strains, ordinary Wistar control rats (NCR) and Wistar-Kyoto normotensive rats (WKR). Each group consisted of 10-11 rats. The animals were kept in metabolic cages. Experiments were performed on standard diet (5-8 mmol Na+/100 g food) and with an increased (15.6 and 56.0 mmol Na+/100 g food) salt intake. At 7 weeks of age, when SHR are in a borderline phase of hypertension, they exhibited a decreased urinary sodium excretion, and an increased urinary noradrenaline excretion compared to controls. The latter might reflect an increased overall activity of the sympathetic nervous system. Urinary dopamine excretion was also increased probably mirroring a higher activity in a renal natriuretic dopamine system. Plasma renin activity and urinary aldosterone excretion were depressed. At 16 weeks of age, when SHR are in an early establishment phase of hypertension, urinary sodium excretion was still lower in SHR, while urinary noradrenaline and dopamine excretions had become normal compared to controls. Plasma renin activity and urinary aldosterone excretion remained depressed. Urinary PGE2 excretion, only determined in this age group, was significantly higher in SHR.

Exaggerated pressor responsiveness to norepinephrine in nonazotemic diabetes mellitus

Pressor responses to norepinephrine (NE) or angiotensin II (AII) were studied in 27 diabetic patients without heart or renal failure and in 27 normal subjects. Mean plasma or 24-hour urinary sodium, blood volume and preinfusion plasma NE levels were similar in diabetic and normal subjects; exchangeable sodium was higher (p less than 0.02) and preinfusion plasma renin activity (PRA) was slightly lower in diabetic patients. The NE pressor and threshold doses were lower in diabetic patients than in normal subjects (76 versus 141 and 16 versus 41 ng/kg/min, respectively; p less than 0.05). The AII pressor dose also tended to be lower in diabetic patients (7.2 versus 11.9 ng/kg/min; p less than 0.05), but the AII threshold dose did not differ between the two groups (1.1 versus 1.6 ng/kg/min). These findings were similar in the diabetic subgroup without or with retinopathy (N = 13 and 14, respectively) and in those with normal or high blood pressure (N = 17 and 10, respectively). These observations suggest that in nonazotemic diabetes mellitus increases in AII pressor responsiveness are associated with a concomitant reduction in PRA. However, cardiovascular pressor responsiveness to NE tends to be exaggerated despite normal plasma NE levels and this alteration may occur already in the normotensive stage of diabetes mellitus. Cardiovascular hyperresponsiveness in diabetic subjects may be related to excess body sodium or structural alterations in the vasculature, or both.

Conditions for stimulation of renin release by cyclic AMP in anaesthetized dogs

Cyclic AMP (cAMP) is the intracellular mediator of beta-adrenergic stimulation in most tissues. Stimulation of beta-adrenoceptors increases renin release much more at low than at control arterial perfusion pressure. If beta-adrenergic stimulation is mediated by cAMP, this nucleotide should also potentiate renin release at low perfusion pressure. In anaesthetized, propranolol treated dogs, the dibutyryl derivative of cAMP (DB-cAMP), which penetrates cell membranes more readily than cAMP, increased renin release significantly during renal arterial constriction at a perfusion pressure below the range of autoregulation, but no significant effect was observed at control blood pressure. A dose-response relationship could be demonstrated in propranolol treated dogs by administering DB-cAMP at 10, 100 and 1000 micrograms/min at low but not at control blood pressure. Since sodium excretion increased, stimulation of a macula densa mechanism is unlikely, whereas arteriolar dilation, caused by autoregulation at low blood pressure, may condition the juxtaglomerular apparatus for renin release. Infusion of cAMP had no effect on renin release either at control or low blood pressure, whereas 5'AMP exerted a marked inhibitory effect at low blood pressure. We conclude that infusion of DB-cAMP rather than cAMP stimulates renin release at low but not at control blood pressure and that this effect is not mediated by beta-adrenergic receptors; cAMP may be an intracellular mediator of renin release.