Humoral and cellular effects of the K+-channel activator cromakalim in man

Summary The effect of cromakalim, a K⁺-channel activator, on the plasma renin-angiotensin-aldosterone system, catecholamines and -atrial natriuretic peptide, and on the intraerythrocyte concentration and transmembrane fluxes of Na⁺ and K⁺ has been investigated in 18 normal male subjects, in a double-blind parallel study. After a run-in period on placebo for 1 week, the subjects were treated either with placebo (n=6) or cromakalim (n=12) for 1 week.Plasma renin activity was significantly increased during cromakalim. No effect of cromakalim on plasma angiotensin II, aldosterone, adrenaline, noradrenaline and -atrial natriuretic peptide was demonstrated. The intra-erythrocyte K⁺ concentration was decreased during cromakalim administration and Ca²⁺-dependent K⁺-channels in red blood cells were increased.     

Effect of cimetidine on the pharmacokinetics and pharmacodynamics of enalapril in normal volunteers

The possible effects of cimetidine on the pharmacokinetics and pharmacodynamics of enalapril, a pro-drug requiring hepatic de-esterification to an active angiotensin-converting enzyme (ACE) inhibitor enalaprilat, were assessed in a randomized, crossover study. Cimetidine (400 mg) or placebo was administered orally every 12 h for 3 days and on the day of a single oral administration of enalapril maleate (10 mg) to seven healthy male subjects. Serum ACE, plasma renin activity (PRA), plasma aldosterone concentration (PAC), and alpha-human atrial natriuretic peptide (alpha-hANP) were measured before and 4 h after the enalapril dosing. There were no significant differences in any serum- and urine-derived kinetic parameters of enalapril and enalaprilat, nor in hemodynamics, PAC, or alpha-hANP between the two treatment trials. ACE decreased and PRA increased to a similar extent in the two trials. Serum enalaprilat concentration correlated significantly (p less than 0.001) with percentage of inhibition of ACE activity. The results suggest that the pharmacokinetics and pharmacodynamics of enalapril are unaffected by preadministration of cimetidine. Thus, cimetidine does not appear to alter hepatic esterase activity toward enalapril.     

Diagnostic evaluation of plasma aldosterone concentration to plasma renin activity ratio in primary aldosteronism

Using the plasma aldosterone concentration to plasma renin activity ratio (PAC/PRA ratio) as the screening test of choice for primary aldosteronism in hypertensive patients, we studied the clinical characteristics and the diagnostic value of PAC/PRA ratio in primary aldosteronism. The plasma aldosterone concentration (PAC) and plasma renin activity (PRA) levels were measured by radioimmunoassay in 902 hypertensive patients from out-patient clinics or hospitals. One hundred and twenty-six suspected primary aldosteronism patients whose PAC/PRA ratio was > 25 ng/dL/ng/mL/hr had a lamellar computed tomography (CT) scan in the adrenal gland and follow-up visits. The proportion of primary aldosteronism in hypertensive patients was 14% (126/902). There were 54 patients with unilateral or bilateral hyperplasia and 25 patients with adenoma according to the CT scan. 39% (49/126) of the patients with primary aldosteronism had hypokalemia. Twenty-five patients received surgical treatment. The efficacy and cure rates were 100% (25/25) and 48% (12/25), respectively. The effective rate of aldactone and the single-drug cure rate were 89% (48/54) and 24% (13/54), respectively. Primary aldosteronism affects over 10% of hypertensive patients in China. The PAC/PRA ratio can be considered as a routine screening test in hypertensives, especially resistant hypertensive patients and a high PAC/PRA ratio is an invaluable index in primary aldosteronism diagnosis. __________ Translated from Chinese Journal of Cardiology, 2006, 34(10): 873–876 [译自: 中华心血맜病杂志]     

Evidence that endogenous somatostatin (SRIF) exerts a tonic inhibitory effect on the rat renin--angiotensin--aldosterone system.

The bolus ip. administration of a SRIF antagonist (SRIF-A) (60 nM/rat) significantly increased renin activity (PRA) and plasma aldosterone concentration (PAC) in rats, without affecting natremia, kalaemia and the blood levels of ACTH or corticosterone. SRIF-A also raised PAC in rats whose renin-angiotensin system had been pharmacologically interrupted by combined captopril/angiotensin-II infusion and in which PRA was very low. The ip. injection of an equimolar dose of SRIF completely reversed these effects of SRIF-A, but the administration of SRIF alone did not affect either PRA or PAC. Taken together, these data would suggest that, in the rat, endogenous SRIF exerts, under basal conditions, a two-fold maximum tonic inhibitory effect on both renin release by kidneys and aldosterone secretion by zona glomerulosa cells.     

SODIUM AND VOLUME DYSREGULATION AFTER APPARENTLY NORMAL PREGNANCY IS SUGGESTED BY ABNORMAL LEVELS OF ATRIAL NATRIURETIC PEPTIDE, RENIN AND ALDOSTERONE

1. Plasma atrial natriuretic peptide (ANP), renin activity, aldosterone, sodium, potassium and serum total protein and albumin during and after 14 normal pregnancies were compared with age-matched controls. 2. None developed toxaemia and all delivered healthy babies. 3. During pregnancy, plasma renin activity and aldosterone were significantly (P less than 0.01) higher and potassium, total protein and albumin significantly lowew (P less than 0.01) than in controls, while ANP was not different from the control level. 4. At 6-13 weeks postpartum, a significant (P less than 0.01) suppression of renin and aldosterone was accompanied by significant (P less than 0.01) elevation of atrial natriuretic peptide when compared with controls. 5. The hormonal changes are consistent with 'effective plasma volume' reduction during pregnancy and persistent volume expansion after pregnancy, perhaps due to a renal glomerular lesion sustained late in pregnancy. In contrast, levels of potassium, total protein and albumin are consistent with haemodilution during pregnancy and its correction postpartum. 6. Measurements available in seven women 40-120 weeks postpartum showed normal renin and aldosterone levels in most, but ANP was still elevated. 7. Pregnancy may have a protracted effect on volume regulation.     

EFFECTS OF ALTITUDE ON ATRIAL NATRIURETIC PEPTIDE: THE BICENTENNIAL MOUNT EVEREST EXPEDITION

1. Overnight recumbent atrial natriuretic peptide levels were significantly elevated in all ten subjects of the Australian Bicentennial Mount Everest Expedition during the first week at 5400 m, during acclimatization. 2. Twenty-four hour urine volume and urine sodium increased markedly at altitude. 3. Plasma renin activity and plasma aldosterone levels decreased significantly at altitude. 4. No significant changes in plasma cortisol, plasma sodium or potassium, body temperature, systolic or diastolic blood pressure or heart rate were observed. 5. Although it was impossible to control or measure salt and water intake during the study, results suggest that atrial natriuretic peptide may be important in the reduction in renin and aldosterone levels and in the diuresis and natriuresis necessary to adapt to hypoxia at altitude.     

Effects of dilevalol,an R,R-isomer of labetalol,on blood pressure and renal function in patients with mild-to-moderate essential hypertension

Summary The effects of oral dilevalol (an R, R-isomer of labetalol), a new -adrenoceptor blocker with ₂-receptor stimulating and -recepter blocking properties on blood pressure, renal function, plasma renin activity (PRA) and plasma aldosterone have been studied in 15 patients with mild-to-moderate essential hypertension treated with it for 6 weeks.Two patients with apparent treatment failure and one patient who developed muscle pain and cramps, and had an elevated creatine phosphokinase level, were excluded from the study.Dilevalol monotherapy 100 mg once daily for 6 weeks significantly lowered both the systolic and diastolic blood pressure compared to placebo. Total renal vascular resistance was significantly reduced, and RBF and GFR remained unchanged. Dilevalol significantly decreased PRA.The results suggest that prolonged daily treatment with dilevalol preserves renal function and produces a concomitant hypotensive action in patients with mild-to-moderate essential hypertension. The ancillary pharmacological properties of dilevalol rather than PRA suppression may be relevant to its renal effects.     

INCREASE IN SERUM TOTAL ANGIOTENSIN-CONVERTING ENZYME ACTIVITY WITH ENALAPRIL THERAPY IN HUMANS: A CONTROLLED TRIAL

1. In a controlled, randomized double-blind trial, 15 patients with essential hypertension were treated with enalapril 5-20 mg/day, or doxazosin 1-8 mg/day, during a 7 week dose titration phase. This was followed by 7 weeks of combined treatment with doxazosin and enalapril. 2. Blood was taken after a 2 week placebo run-in phase, and at 3 and 7 weeks in the single-agent and combined treatment phases, for measurement of plasma renin activity (PRA), plasma angiotensin II (AII), plasma aldosterone and serum free and total angiotensin-converting enzyme (ACE) activities. 3. Doxazosin had no effect on serum free or total ACE activities. 4. Enalapril reduced serum free ACE activity and increased serum total ACE activity, which at 7 weeks was significantly greater than in patients receiving doxazosin. 5. In those patients who received enalapril, 10 mg/day for 3 weeks and then 20 mg/day for 4 weeks (n = 12), with or without doxazosin, mean serum total ACE activity increased by 51%. PRA was also increased in this group, but there were no changes in plasma AII or aldosterone concentrations.     

Effect of human atrial natriuretic peptide on blood glucose concentrations and hormone stimulation during insulin-induced hypoglycaemia in healthy man

Summary A double-blind placebo-controlled study using the double-dummy technique has been done to examine whether the responses of pituitary and adrenal hormones to insulin-induced hypoglycaemia were impaired by a pharmacological dose of human atrial natriuretic peptide (human ANF-(99-126), hANP).After an overnight fast eight male healthy volunteers (aged 23–40 years) received in random order i.v. bolus injections of insulin 0.125 U·kg^–1 + placebo, hANP 100 µg + placebo, insulin + hANP, or both placebo preparations.In the insulin-only experiment, human growth hormone, adrenocorticotrophic hormone, cortisol, aldosterone, plasma renin activity, adrenaline, and noradrenaline were all stimulated by hypoglycaemia.In the hANP-only experiment there were no hormonal changes other than decreases in plasma renin activity and aldosterone concentration. In the insulin + hANP experiment the nadir of blood glucose was decreased to 1.3 from the 2.0 mmol·1^–1 found in the insulin-only experiment. The exaggerated hypoglycaemia resulted in increased stimulation of human growth hormone, adrenocorticotrophic hormone and adrenaline when compared to the insulin-only experiment. The rise in the cortisol and aldosterone concentrations was only slightly increased, and the stimulation of plasma renin activity was blunted.Unexpectedly, hANP was found to enhance the hypoglycaemic action of insulin, most probably by inhibiting insulin degradation within the liver. There was no evidence of an inhibitory effect of hANP on the stimulation of pituitary or adrenal hormones during insulin-induced hypoglycaemia. The reduction in renin may indicate an inhibitory action of hANP on catecholaminergic effects within the kidney.     

ATRIAL NATRIURETIC PEPTIDE INHIBITS THE ALDOSTERONE RESPONSE TO METOCLOPRAMIDE IN PATIENTS WITH GLOMERULAR DISEASE AND ESSENTIAL HYPERTENSION

1. We examined the effects of metoclopramide (MCP: 10 mg i.v.) on plasma atrial natriuretic peptide (ANP) and aldosterone concentrations (PAC) and the effect of ANP on MCP-induced PAC in four patients with primary glomerular diseases and seven patients with essential hypertension. 2. MCP injection caused no significant changes in plasma ANP. MCP produced a marked increase in PAC without a significant change in plasma renin activity. 3. The increase in PAC induced by MCP injection was markedly attenuated when preceded by the infusion of ANP (25 ng/kg per min). 4. These results suggest that the dopaminergic D₂ mechanism is not involved in the regulation of ANP secretion and that ANP modulates the dopaminergic regulation of aldosterone secretion.     

The effect of atrial natriuretic peptide on plasma renin activity,plasma aldosterone,and urinary dopamine in man

Summary The acute natriuretic effect of human atrial natriuretic peptide (ANP) has been well described in man. We have now studied possible hormonal mediators of this effect.We studied six healthy volunteers on two occasions when they received either an infusion of ANP of 1.5 pmol·kg^–1·min^–1 for 30 min followed by 15 pmol·kg^–1·min^–1 for a further 30 min, or matching vehicle infusions in a randomized single-blind fashion.On the placebo day, plasma renin activity (PRA) rose from 1.26±0.08 to 1.57±0.14 ng A1·ml^–1·h^–1, while on the ANP study day PRA fell from 1.45±0.15 to 1.28±0.05 ng A1·ml^–1·h^–1 (p<0.01). No significant changes were found in plasma aldosterone concentrations or in urinary dopamine excretion.These results provide evidence that ANP suppresses renin release in man.     

Activity of the renin-angiotensin-aldosterone (RAA) and secretion of the atrial natriuretic peptide (ANP) in patients with chronic renal failure.

In 12 patients with chronic renal failure (CRF) treated with haemodialyses and in 21 healthy controls plasma renin activity (PRA) and the concentrations of aldosterone and atrial natriuretic peptide (ANP) were determined in serum before and after blockade of the angiotensin converting enzyme with captopril. The study was carried out under conditions of the so called bed rest test (BR) and water immersion test (WI). After captopril administration a significant rise of PRA was noted in both groups with a drop of aldosterone level which was significant only in the control group. Captopril administration had no effect on serum ANP level. The results of the study are not suggesting the presence of a close relationship between ANP secretion and the activity of the RAA system in healthy controls and in CRF patients.     

Inhibition of the aldosterone response to sodium depletion in man by stimulation of dopamine DA2 receptors

Summary In this study we have investigated the effect of co-dergocrine, a selective DA₂-agonist, on plasma aldosterone concentrations (PAC) in twelve patients with essential hypertension both in basal conditions and during sodium depletion.Sodium depletion resulted in an increase of PAC from 38 (13) pg/ml to 297 (21) pg/ml. The PAC response to sodium depletion was reduced to 155 (29) pg/ml by co-dergocrine.No significant PAC changes were found in patients maintained on a normal sodium intake. In addition the drug did not significantly modify plasma renin activity (PRA) in either experimental group.These results suggest that the dopaminergic inhibition of aldosterone secretion in man is mediated by DA₂-receptors in the adrenal cortex.     

Circadian rhythm of the renin-angiotensin-aldosterone system in the rat

The 24 h-course of plasma renin activity (PRA), plasma aldosterone concentration (PAC), plasma corticosterone concentration (PCC) and of the urinary excretion of sodium, potassium and aldosterone was investigated in male Sprague-Dawley rats under different experimental conditions. The data obtained can be summarized as follows: 1. The renin-angiotensin-aldosterone system (RAAS) of the rat is subject to a circadian rhythm which is largely in phase with the well-known rhythm of the pituitary-adrenal axis. This rhythm can be demonstrated in PRA as well as in plasma concentrations and urinary excretion rates of aldosterone. The rhythm of urinary excretion of electrolytes is unlikely to be due to the rhythm of aldosterone secretion. 2. The light-dark cycle is the main synchronizer for these rhythms: inverting the light-dark cycle for 5 weeks entirely inverts the rhythms of all the parameters cited. 3. A dissociation of the rhythms of PRA and PAC can be observed following sodium restriction or dexamethasone treatment. A role of ACTH IN regulating the rhythmic pattern of aldosterone secretion is suggested by the finding that PAC and PCC follow the same pattern of circadian variations under every experimental condition tested. 4. The responsiveness of the RAAS to stimulation or suppression varies with the time of day. 5. It is suggested that experiments ought to be performed not only during the inactive (light hours) but also during the active (dark hours) phase when investigating the RAAS in the rat. This can conveniently be achieved by the use of an animal room with a reversed lighting regime.     

Effects of felodipine on atrial natriuretic peptide in hypertensive non-insulin dependent diabetes mellitus.

Eighteen patients with non-insulin dependent diabetes mellitus and hypertension were treated during two 4 week periods with the calcium antagonist felodipine or placebo in a double-blind, randomised, cross-over study. Mean systemic blood pressure was significantly lower on felodipine, without producing a deleterious effect on diabetic control. Felodipine was associated with an increment in plasma renin concentration but plasma aldosterone and the renal outputs of sodium and dopamine were similar on both treatments. Plasma atrial natriuretic peptide levels were significantly reduced following felodipine treatment.     

Changes in haemodynamics and body fluid volume due to enalapril in patients with essential hypertension on chronic diuretic therapy

Summary In 12 patients with essential hypertension who remained hypertensive despite chronic chlorthalidone treatment, the effect of 2 weeks of additional therapy with the converting enzyme inhibitor (CEI) enalapril on blood pressure and body fluid volumes has been evaluated. The objective was to examine the influence of a diuretic-stimulated renin-angiotensin-aldosterone system (RAAS) on haemodynamics and body fluid volume. Mean arterial pressure (MAP –21%), total peripheral resistance index (TPRI –22%) and plasma aldosterone concentration (PAC –39%) were decreased, and plasma renin activity (PRA 660%) was increased. The average heart rate (HR), cardiac index (CI), plasma volume (PV), blood volume (BV), extracellular fluid volume (ECFV) and body weight (BW) remained unchanged. A negative correlation was found between the per cent changes in ECFV and PAC. Thus, body fluid volumes during chronic diuretic treatment are well preserved even when the RAAS with its sodium retaining properties is suppressed by CEI. Possible mechanisms are a volume (not angiotensin II) — dependent stimulation of aldosterone and a fall in blood pressure.     

EFFECT OF ARTERIAL CHEMORECEPTOR STIMULATION WITH ALMITRINE BISMESYLATE ON PLASMA RENIN ACTIVITY, ALDOSTERONE, ACTH AND CORTISOL IN ANAESTHETIZED, ARTIFICIALLY VENTILATED CATS

1. Changes in plasma renin activity (PRA) and in the plasma concentration of aldosterone, adrenocorticotrophic hormone (ACTH) and cortisol in response to an intravenous infusion of the chemoreceptor stimulant almitrine bismesylate (0.2 mg/kg) were studied in two groups of anaesthetized, paralysed and constantly ventilated cats. In one group, the peripheral arterial chemoreceptors remained innervated, whereas in the other they were denervated by bilateral cervical vagotomy and section of the carotid sinus nerves. 2. Animals with innervated chemoreceptors (n= 16) reacted to almitrine bismesylate with a significant (P < 0.05) increase in both ACTH and cortisol. These responses were not present in cats in which the peripheral arterial chemoreceptors had been surgically denervated (n= 16). 3. Plasma renin activity and plasma aldosterone increased with time during experiments on both the chemoreceptor-intact and chemoreceptor-denervated cats. Almitrine did not affect the time course of the rise in PRA and plasma aldosterone in either group of animals. 4. These data indicate that, under the conditions of our experiments, almitrine induced arterial chemoreceptor reflex mechanisms stimulate ACTH and cortisol release, but has no chemoreceptor-dependent influence on PRA or plasma aldosterone.     

Effects of once daily indapamide and pindolol on blood pressure,plasma aldosterone concentration and plasma renin activity in a general practice setting

Summary Sixteen patients with essential hypertension completed a double blind factorial trial comparing the effects of indapamide (2.5 mg daily) and pindolol (10 mg daily) on blood pressure, heart rate, plasma renin activity and plasma aldosterone concentration. There were four randomised test phases of eight weeks each during which patients received indapamide alone, pindolol alone, indapamide plus pindolol and no active treatment (placebo). Blood pressure and heart rate were measured every two weeks. Supine mean arterial pressure fell from 117 mm Hg in the placebo phase to 111 mm Hg in the indapamide phase, 106 mm Hg in the pindolol phase and 103 mm Hg in the combined indapamide plus pindolol phase. Factorial analysis confirmed that the hypotensive effects of the two drugs were additive, without evidence of potentiation or antagonism. Indapamide caused significant reductions in plasma potassium and chloride, and increases in plasma bicarbonate and urate concentrations; it also caused increases in plasma renin activity and aldosterone concentration. These changes are similar to those observed with thiazide diuretics.     

Beta-adrenoceptor blockade potentiates exercise-induced release of atrial natriuretic peptide

Summary The effect of a non selective and a cardio-selective beta-blocker on basal and exercise-stimulated plasma atrial natriuretic peptide concentrations in healthy volunteers has been studied. Nine healthy volunteers received single oral doses of 5 mg tertatolol, 100 mg atenolol or placebo, at one week intervals, in a double blind cross over trial.At rest plasma atrial natriuretic peptide, aldosterone, antidiuretic hormone and cyclic GMP concentrations and plasma renin activity were not modified by the treatments. During exercise plasma atrial natriuretic peptide concentrations were significantly increased by each treatment, the increment being significantly greater on beta-blockers than on placebo. The rise in atrial natriuretic peptide was 72% after placebo (from 24 to 42 pg/ml), 184% after atenolol (from 30 to 86 pg/ml), and 183% after tertatolol (from 34 to 95 pg/ml), respectively.Thus, the study has shown that in healthy subjects the plasma natriuretic peptide concentration is increased by exercise and that the increase is considerably and equally potentiated by selective and non selective beta-adrenoceptor blockade. The effect may be mainly due to a reduction in ventricular contractility with an increase in atrial pressure. The beta-blockers did not influence the resting plasma atrial natriuretic peptide levels, which suggests that in healthy subjects basal atrial natriuretic peptide secretion is not controlled via beta-receptors.     

Effect of chronic diuretic treatment on the plasma renin-angiotensin-aldosterone system in essential hypertension.

1 Chronic treatment with a constant dose of hydrochlorothiazide or tienilic acid increases plasma renin activity (PRA) acutely to reach a maximum within the first week. 2 During chronic diuretic therapy from 1 month to 1 year, PRA remained elevated at a rather constant level, though this was somewhat lower than the maximum level reached after 1 week. 3 A significant (P less than 0.01) correlation (r = 0.74) between changes in plasma angiotensin II and renin activity provoked by chronic treatment for 3 months with hydrochlorothiazide and tienilic acid was found. 4 The increase in plasma aldosterone during chronic treatment with hydrochlorothiazide and tienilic acid (1000 mg) is related (r = 0.68; P less than 0.01) to the rise in plasma angiotensin II.