Rise In Plasma Renin Activity Research Articles

Effects of blood viscosity on renin secretion

The effects of alterations in blood and plasma viscosities on plasma renin activity (PRA) were studied in dogs anesthetized with pentobarbital. Blood viscosity was altered by changing the hematocrit (Hct) level by isovolemic exchange using packed red blood cells or plasma. Plasma viscosity was elevated by isovolemic exchange using Hct-matched blood with high molecular weight dextran (Dx, mean m.w. approximately 450,000) dissolved in plasma. Following control measurements of plasma and blood viscosities, plasma [Dx], PRA, Hct and hemodynamic functions, the dog was subjected to isovolemic exchange transfusions to either alter the Hct or administer the Dx. Various measurements were repeated 40-60 min after each exchange. Arterial pressure and renal blood flow remained relatively constant after exchanges; increases in plasma and blood viscosities were accompanied by a decrease in renal vascular hindrance (vasodilation) to keep the renal flow resistance at control level. PRA rose with increases in plasma [Dx] and viscosity, and the rise in PRA was best correlated with the decrease in renal hindrance. The changes in PRA and renal hindrance have the same regression line whether blood viscosity was altered by Hct variation or Dx administration. The results indicate that increases in viscosity cause a compensatory vasodilation of renal vessels to cause renin secretion.

Time-related Changes in Plasma Adrenal Steroids During Treatment With Spironolactone in Primary Aldosteronism

Time-related changes in plasma levels of aldosterone, deoxycorticosterone, corticosterone, and cortisol were studied during treatment with spironolactone in 8 patients with primary aldosteronism due to adenomas. Plasma renin activity (PRA), serum sodium and serum potassium were also measured. The patients were treated with spironolactone, 75 to 225 mg daily, and blood samples were withdrawn on days 7, 14, and 21 to 28 of drug administration. Plasma aldosterone concentrations (PAC) were not altered by spironolactone; however, significant increases were observed in plasma deoxycorticosterone on days 21 to 28 and in plasma corticosterone and cortisol on days 14 and 21 to 28. The suppressed PRA values were markedly increased on days 21 to 28 and low levels of serum potassium returned to the normal range on day 7. The lack of increase in PAC, despite a remarkable rise in PRA and serum potassium, suggests biosynthetic inhibition of spironolactone at the sites of 18-hydroxylation and/or 18-oxidation, because of the elevation of deoxycorticosterone and corticosterone.

Pharmacodynamic, pharmacokinetic and humoral effects of oral zabicipril, an angiotensin converting enzyme inhibitor in normotensive man.

1. Zabicipril, S9650, a new angiotensin converting enzyme inhibitor, was administered to salt-replete, normotensive males in single doses of up to 10 mg. 2. The safety, tolerance and dose-response relationship with regard to inhibition of plasma ACE activity were characterised initially in an open, pilot, dose-finding study in 12 subjects and further explored in a double-blind, parallel group, placebo controlled study in another 30 subjects. 3. The drug was generally well tolerated and produced no change in routine haematology or serum biochemistry tests. 4. Dose related (0.03 to 10 mg) inhibition of plasma converting-enzyme was observed, with 2.5 mg of zabicipril producing over 90% inhibition at 4 h and 60% at 24 h. 5. There were no significant changes in blood pressure or heart rate in normotensive subjects over the dose range studied. 6. A dose related rise in plasma renin activity and angiotensin I was observed. No dose related reduction in plasma aldosterone was observed. 7. These initial studies suggest that zabicipril is a well tolerated inhibitor of converting enzyme with near maximal inhibitory effect occurring at a dose of 2.5 mg. Further exploration of the dose range after single and multiple doses is indicated.

Acromegaly and hypertension: Prevalence and relationship to the renin-angiotensin-aldosterone system

The prevalence of arterial hypertension was evaluated in a retrospective study of 158 patients with acromegaly, and results were compared to control populations, namely, the Munich Blood Pressure Study (MBPS) and the Framingham Study. The prevalence of hypertension (defined according to WHO criteria) was significantly increased in female patients but not in men; hypertensive acromegalics were older and tended to have higher body weight compared to normotensive patients. Hypertension was not related to serum concentrations of growth hormone. After successful treatment of acromegaly, growth hormone levels and systolic and diastolic blood pressure fell only in female hypertensive acromegalics; this did not occur in normotensives. The rise in plasma renin activity in response to upright posture was diminished in 57.9% of acromegalic patients. The prevalence of low-renin hypertension in our group of patients was 31.6%, which is similar to figures reported for unselected non-acromegalic subjects with essential hypertension. Orthostatic renin activity was weakly and inversely related (r = -0.3) to blood pressure. No relationship between plasma aldosterone concentration and blood pressure could be detected; however, in acromegalic women, aldosterone rose higher after ambulation than in men. In conclusion, hypertension is a common problem in acromegaly and at least in part related to similar risk factors in control populations. The association with abnormalities of the renin-angiotensin-aldosterone system is difficult to interpret and does not offer an explanation for the slight increase in the prevalence of hypertension.

Acute Physiological Changes in Canine Kidneys Following Exposure to Extracorporeal Shock Waves

Nine anesthetized dogs were studied for four to five hours after administration of extracorporeal shock waves to one kidney, the contralateral organ serving as control. Urinary excretion of electrolytes, N-acetyl-β-glucosaminidase (NAG) and kallikrein, clearances of creatinine, inulin and para-amino-hippuric acid (PAH), serum aldosterone level and plasma renin activity (PRA) were determined.On the exposed side there was a significant increase in urinary flow and urinary NAG excretion, and a significant fall in urinary osmolality. Effective renal plasma flow (ERPF) was reduced and glomerular filtration rate (GFR) unchanged, thus filtration fraction (FF) was increased. Extraction of PAH was significantly reduced compared with the control kidney.On the control side there was a significant increase in urinary flow and excretion of electrolytes, and a significant fall in urinary osmolality. GFR was increased and ERPF unchanged. FF therefore increased also on this side. The mean rise of PRA in the exposed kidney was higher than in the control kidney, the difference being not significant (p = 0.09).Our results may indicate a triggering of the renin-angiotensin system, and an effect on proximal tubular function following exposure of extracorporeal shock waves. (J. Urol, 143:1280-1283, 1990)

Converting-enzyme inhibition abolishes polydipsia induced by dietary NaCl and K depletion

The present studies were designed to test the hypothesis that angiotensin II (ANG II) mediates nonosmotic thirst in animals fed the low-NaCl K-free diet by preventing the increased generation of ANG II using the converting-enzyme inhibitor, enalapril. Animals were fed either a control salt or low-NaCl K-free diet and were treated with or without enalapril. Water intake in rats fed the low-NaCl K-free diet increased more than twofold on day 3 and remained elevated over the 10-day period of study. Treatment with enalapril (40 mg.kg-1.day-1) 1) prevented the striking rise in plasma renin activity in rats fed the low-NaCl K-free diet, 2) led to complete blockade of the pressor response to a 50-ng injection of angiotensin I but not ANG II, 3) did not affect daily water intake in rats consuming the control salt diet, 4) did not reduce basal water intake in rats fed the low-NaCl K-free diet below values measured in control animals, and 5) did not abolish water intake in response to osmotic stimulation. However, enalapril treatment abolished the increase in water intake that occurs in animals fed the low-NaCl K-free diet. In a double crossover study using two groups of rats fed the low-NaCl K-free diet, enalapril prevented increased water intake in rats initially fed the low-NaCl K-free diet and rapidly inhibited increased water intake in rats fed the low-NaCl K-free diet after the high water intake had been established.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of histamine H2‐receptor blockade on the cardiovascular reflex response to lower‐body negative pressure in man

The role of histamine H2-receptors in cardiovascular control is unknown. In seven healthy volunteers, we studied how histamine H2-receptor blockade affected the reflex response to hypovolaemia induced by lower-body negative pressure (LBNP). In placebo-treated individuals, LBNP down to -40 mmHg did not change systolic pressure but increased diastolic pressure, heart rate, forearm vascular resistance, plasma noradrenaline concentration and plasma renin activity. After pretreatment with ranitidine, a specific histamine H2-receptor antagonist, the diastolic pressure rise no longer sufficed to maintain a constant systolic pressure during LBNP. Ranitidine pretreatment also attenuated the heart rate response and the rise in plasma renin activity induced by LBNP, but did not significantly change the reflex forearm vasoconstriction or the forearm plasma noradrenaline response. The results suggest that histamine H2-receptor blockade attenuates the reflex vasoconstrictor response to lower-body negative pressure. The mechanism behind this effect remains unknown, but the data do not support the idea that the effect is exerted in the skeletal muscle vascular bed.

Atriopeptin Alters the Vasopressin and Renin Responses Elicited by Hemorrhage

This study was designed to investigate whether an infusion of atrial peptide is capable of modulating the hormonal and hemodynamic responses elicited by acute hemorrhage. Conscious dogs were bled at a rate of 0.8 ml.kg-1.min-1 until 20 ml of blood/kg body wt had been removed. Two experiments were performed on each dog; in one experiment the animal was given alpha-human atrial natriuretic peptide (alpha-hANP) (50 ng.kg-1.min-1) dissolved in saline; in the other only the saline vehicle was given. Right and left atrial pressures decreased during hemorrhage in all experiments; the absolute decreases were greater when the animals received atriopeptin, but the differences between treatments were statistically significant only for right atrial pressure. Cardiac output decreased (P less than 0.05) and total peripheral resistance increased (P less than 0.05) during hemorrhage when atriopeptin was infused; although these variables showed similar trends when vehicle alone was infused during hemorrhage, no significant changes occurred. Infusion of atrial peptide did not affect the decrease in arterial blood pressure that occurred during hemorrhage. The increase in plasma vasopressin induced by hemorrhage was potentiated, but the increase in plasma renin activity was attenuated when alpha-hANP was infused. Hemorrhage increased circulating aldosterone levels in each experiment, but the response was less pronounced when alpha-hANP was given during the experiment. Intravenous administration of alpha-hANP modulates the hemodynamic responses elicited by hemorrhage, potentiates the rise in plasma vasopressin, and attenuates the rise in plasma renin activity induced by acute blood loss in conscious dogs.

Renal and Endocrine Effects of Fenoldopam and Metoclopramide in Normal Man

The effects of fenoldopam (FD), a selective dopamine-1 (DA1) agonist in doses from 0.05 to 0.50 micrograms/kg/min and of the aselective dopamine antagonist metoclopramide (MCP) on blood pressure (BP), sodium excretion and renal hemodynamics were investigated in 10 healthy volunteers. During FD infusion the diastolic BP fell 9 mm Hg with a rise in heart rate. During combined infusion of FD and MCP no changes in BP occurred. Effective renal plasma flow rose for all doses of FD with a maximal increase of 36% and was not influenced by MCP infusion. Glomerular filtration rate remained unchanged. FD induced an increase in sodium and calcium excretion compared to placebo study, which was abolished by MCP. A marked rise of plasma renin activity during FD infusion was noted, blunted by MCP. MCP induced a marked increase of aldosterone, sustained, but blunted, during subsequent FD infusion, suggesting a DA1-mediated influence on aldosterone secretion. During infusion of FD alone, an increased urinary dopamine excretion was observed. We conclude that FD induces: (1) systemic and renal vasodilation and (2) natriuresis by direct stimulation of DA1 receptors in the proximal tubule, which is (partially) counteracted by a rise of plasma renin activity and subsequently of aldosterone.

EFFECTS OF LOW DOSE INFUSION OF ATRIAL NATRIURETIC FACTOR ON ACUTE INHIBITION OF ANGIOTENSIN CONVERTING ENZYME IN NORMAL MAN

1. We have studied the effects of low dose infusions of atrial natriuretic factor (human ANF (99-126), 1.95 pmol/min per kg) on angiotensin converting enzyme (ACE) inhibitor-induced haemodynamic and hormonal changes in healthy subjects. 2. ACE inhibitor (captopril 25 mg, administered orally) was given against a background infusion of physiological saline (placebo day) or ANF (experimental day). 3. Compared with the placebo observations, ANF enhanced the fall in plasma aldosterone concentrations induced by captopril (P less than 0.05). 4. The rise of plasma renin activity following administration of ACE inhibitor which was observed during placebo infusion was abolished by ANF (P less than 0.05). 5. The responses of systemic blood pressure and heart rate to the converting enzyme inhibition were not affected by the infusion of ANF. 6. These results suggest that variations in endogenous circulating ANF may influence, in part, the response of these hormonal levels during ACE inhibition.

Antihypertensive contribution of sodium depletion and the sympathetic axis during chronic angiotensin II converting enzyme inhibition

The known physiological adaptation of cardiovascular sensitivity to variations in angiotensin II (Ang II) levels would predict that the blood pressure (BP)-lowering effect of Ang II inhibition might be at least partly counterbalanced by enhanced Ang II reactivity. Therefore, factors other than Ang II inhibition per se may contribute to the antihypertensive mechanisms of angiotensin converting enzyme (ACE) inhibitors. In order to further investigate this, the body sodium-blood volume state as well as the pressor reactivity to infused Ang II or norepinephrine (NE) were assessed in 12 normal subjects and 16 patients with essential hypertension given a placebo, and after 6 weeks of intervention with enalapril (20-40 mg/day). Enalapril produced in both groups similar falls in plasma ACE activity (P less than 0.0001) and upright plasma aldosterone (P less than 0.01), and a rise in plasma renin activity (PRA; P less than 0.05). BP decreased from 156/107 +/- 3/2 (mean +/- s.e.m.) to 142/94 +/- 5/3 mmHg (P less than 0.001) in the hypertensives and from 118/84 +/- 4/2 to 111/73 +/- 4/3 mmHg (P less than 0.01) in the normal subjects. In the hypertensive patients only, the Ang II pressor reactivity relative to Ang II plasma levels during Ang II infusion was increased (P less than 0.01), while the NE pressor reactivity relative to NE plasma levels during NE infusion (P less than 0.01) as well as the exchangeable body sodium (-5%, P less than 0.001) were reduced significantly. Blood and plasma volume, levels of plasma atrial natriuretic factor and catecholamines, and the heart rate and its response to isoproterenol were unchanged in both groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Modulation of renin by thromboxane: studies with thromboxane synthase inhibitor, receptor antagonists, and mimetic

The regulation of plasma renin activity (PRA) by thromboxane (Tx) A2 was studied in anesthetized rats by measuring PRA before and after administration of drugs that block cyclooxygenase (CO) (indomethacin [INDO], 5 mg/kg), thromboxane synthase (TS) (UK 38485 [UK], 100 mg/kg), or Tx receptors (SQ 29548 [SQ], 8 mg/kg or L 641953 [L], 50 mg/kg) or that activate Tx receptors (U 46619 [U], 10 ng.kg-1.min-1). PRA (ng ANG I.ml-1.h-1) was unaffected by vehicle; it was reduced by INDO (25 +/- 2 to 13 +/- 3, n = 13, P less than 0.001) but was increased by UK (24 +/- 3 to 50 +/- 6, n = 18, P less than 0.005), SQ (27 +/- 4 to 44 +/- 7, n = 6, P less than 0.05), and L (32 +/- 4 to 51 +/- 7, n = 10, P less than 0.05). U reduced PRA in each rat (17 +/- 3 to 10 +/- 3, n = 6, P less than 0.005). UK caused dose-dependent stimulation of PRA (mean effective dose 50 mg/kg) and inhibition of TxB2 excretion (mean inhibitory dose 15 mg/kg). After INDO, SQ no longer changed PRA (-1 +/- 10, n = 7). Prolonged administration of SQ for 4-6 days (20 mg.kg-1.day-1 ip) did not change Na+ or K+ balances, blood pressure, renal hemodynamics, or urine flow. However, SQ stimulated PRA (P less than 0.007) independent of prior salt intake. In conclusion in anesthetized rats 1) PRA is stimulated by products of CO but inhibited by products of TS and by a Tx mimetic; 2) stimulation of PRA by SQ depends on ongoing PG and Tx synthesis; 3) rise in PRA with Tx antagonists is not closely related to changes in salt balance, blood pressure, or renal hemodynamics.

The effects of calcium-blocking agents on sympathetic responses to acute haemorrhagic shock in dogs

The effects of three calcium channel-blocking agents, verapamil, nifedipine and diltiazem, given intravenously, have been studied on the cardiovascular and sympathetic responses to acute haemorrhagic shock in anaesthetized dogs. Following acute haemorrhage, cardiac output, mean pulmonary artery pressure, mean right atrial pressure, and pulmonary capillary wedge pressure all fell, and adrenaline, noradrenaline and plasma renin activity rose. In the presence of each calcium antagonist the fall in cardiac output, mean pulmonary artery pressure, central venous pressure and pulmonary capillary wedge pressure was similar, and the rise in catecholamine levels unaffected. The rise in plasma renin activity following diltiazem 0.02 mg kg-1 or 0.1 mg kg-1 or nifedipine 0.01 mg kg-1 was similar to values in a control group, whereas in those receiving verapamil 0.15 mg kg-1 or 0.6 mg kg-1, or nifedipine 0.05 mg kg-1, the rise was greater.

Atrial Natriuretic Factor Attenuates Prostaglandin E2-Stimulated Plasma Renin Activity in Humans

The effect of atrial natriuretic factor (ANF) 99-126 3 or 10 pmol/kg/min on increase in plasma renin activity (PRA) stimulated by a 30-min infusion of prostaglandin E2 (PGE2) 80 ng/kg/min was studied in healthy salt-replete male volunteers. PGE2 increased PRA to approximately 230% of basal levels (p less than 0.001). Concomitant infusion of ANF 3 pmol/kg/min significantly attenuated this rise in PRA to approximately 130% of baseline values (p = 0.02, n = 10). A quantitatively similar effect was observed with ANF 10 pmol/kg/min (n = 5). We suggest, in light of previous findings, that this inhibitory effect of ANF probably represents a nonspecific action rather than a specific effect of ANF on PGE2-mediated increases in PRA.

Reciprocal Changes in Atrial Natriuretic Peptide Levels and Plasma Renin Activity During Treatment of Pulmonary Embolism

We followed atrial natriuretic peptide (ANP) levels in 12 patients during anticoagulant treatment of pulmonary embolism. In each patient with this disorder ANP decreased during treatment. Concomitantly, plasma renin activity (PRA) markedly rose. The decrease in ANP was significantly related to the rise in PRA. No consistent changes in ANP or in PRA were observed in five patients with peripheral venous thrombosis receiving the same anticoagulant treatment. Plasma aldosterone levels did not change in either group.

Mechanism of inhibition of renin response to hypotension by atrial natriuretic factor

We have reported that infusion of atrial natriuretic factor (ANF) inhibited the rise in plasma renin activity (PRA) in response to constriction of the abdominal aorta to cause a reduction in renal perfusion pressure (RPP). To evaluate the effect of ANF on neural control of renin release, acute thoracic inferior vena caval constriction (TIVCC) was performed in conscious dogs to reduce arterial pressure by 25% of control and stimulate PRA by a reflex increase in renal nerve activity and a reduction in RPP. Propranolol was used to block neural stimulation of renin release. TIVCC caused significant increases in PRA, plasma aldosterone, arginine vasopressin (AVP), and adrenocorticotropic hormone (ACTH) concentrations. The increase in PRA was significantly reduced by the infusion of either ANF at 20 ng.kg-1.min-1 or propranolol. The combined infusion of ANF and propranolol produced an additive and complete inhibition of the renin response to TIVCC; therefore the effect of ANF is independent of neural stimulation of renin release. ANF at 20 ng.kg-1.min-1 also inhibited increases in aldosterone, AVP, and ACTH, but ANF at 5 ng.kg-1.min-1 only affected the aldosterone response to TIVCC. Therefore ANF inhibits angiotensin II-stimulated aldosterone synthesis and/or secretion at very low doses and at higher doses attenuates reflex increases in AVP and ACTH caused by hypotension.

Effect of Bopindolol on Renin Secretion and Renal Excretory Function in Rats

We investigated the effects of the new beta-adrenoceptor antagonist, bopindolol, on stimulated renin secretion and on renal function in conscious rats. Intravenous doses of 10, 31.6, and 100 micrograms/kg of bopindolol antagonized the rise in plasma renin activity (PRA) induced by the administration of isoproterenol (10 micrograms/kg, s.c.). Peak PRA, evident at 15 min after isoproterenol, reached 27 +/- 3 ng/ml/h with bopindolol (100 micrograms/kg) pretreatment vs. 105 +/- 7 ng/ml/h in saline controls. Antagonism by bopindolol (100 micrograms/kg, i.v.) of isoproterenol-stimulated rise in PRA persisted through 12 h. Within this dosage range, bopindolol itself had no significant effect on PRA. Significant antagonism of beta-adrenoceptor-induced hypotension resulted with 31.6 and 100 micrograms/kg of i.v. bopindolol. Orally administered bopindolol produced significant antagonism of isoproterenol-induced increase in PRA at a dose of 316 micrograms/kg; however, oral doses of 31.6-316 micrograms/kg of bopindolol failed to significantly alter furosemide-stimulated increase in PRA. Bopindolol alone had little effect on renal excretory function but caused a slight attenuation of furosemide-induced diuresis and electrolyte excretion. Plasma electrolytes and osmolarity were unaffected by bopindolol alone or in conjunction with furosemide. These results indicate that bopindolol (a) is a potent, long-acting, orally active, antagonist of beta-adrenoceptor-stimulated renin secretion in the rat, (b) is ineffective in antagonizing furosemide-induced rise in PRA, (c) does not elevate basal levels of PRA by virtue of its intrinsic sympathomimetic activity, and (d) does not cause dramatic alteration of renal excretory function at effective beta-blocking doses.

Reflex inhibition of plasma renin activity by increased left ventricular pressure in conscious dogs.

The purpose of the present study was to determine the effects of left ventricular (LV) outflow obstruction on plasma renin activity (PRA) and the contribution from afferent receptors located in the LV myocardium. In chronically instrumented, conscious dogs (n = 12), changes in PRA during a 15- to 20-mmHg decrease in arterial blood pressure were assessed during 1) intravenous infusions of nitroprusside (NP) alone and 2) infusions of NP while peak systolic LV pressure was elevated by acute ascending aortic occlusion (AAO + NP). Infusions of NP alone elicited significant increases in heart rate (24.9 +/- 5.1 beats/min; P less than 0.01) and in PRA [3.31 +/- 0.53 ng angiotensin I (ANG I).ml-1.h-1; P less than 0.01]. These were accompanied by decreases in both LV pressure (-13.8 +/- 3.6 mmHg; P less than 0.05) and left atrial pressure (-3.0 +/- 0.7 mmHg; P less than 0.05). During AAO + NP, LV pressure was elevated to an absolute level of 169.2 +/- 4.6 mmHg (+53.3 +/- 4.2 mmHg; P less than 0.001), whereas left atrial pressure was not changed. Both the hypotension-induced rise in PRA and tachycardia were significantly inhibited during AAO + NP (+0.59 +/- 0.29 ng ANG I.ml-1.h-1 and +6.3 +/- 4.6 beats/min, respectively; NS). The topical application of a local anesthetic in the region of the main coronary artery, sufficient to block the heart rate and arterial blood pressure responses to selective LV receptor stimulation by intracoronary veratridine (0.1-0.4 microgram/kg), resulted in significant increases in PRA and heart rate during AAO + NP.(ABSTRACT TRUNCATED AT 250 WORDS)

Enalapril does not alter renal function in normotensive, normoalbuminuric, hyperfiltering Type 1 (insulin-dependent) diabetic children

Using a prospective randomised double-blind crossover design, the effect of the angiotensin converting enzyme inhibitor enalapril compared to a placebo was studied in 18 normotensive, normoalbuminuric Type 1 (insulin-dependent) diabetic children. Each patient had a high normal or clearly elevated glomerular filtration rate (145 ml.min-1.1.73 m2 or higher) in the 6 months prior to the study. Enalapril, 0.5 mg.kg-1.day-1, was given for 4 weeks followed by placebo for 4 weeks, or vice versa. At the end of each period, glomerular filtration rate, renal plasma flow, blood pressure, plasma renin activity, and converting enzyme activity were determined. Enalapril caused significant reduction (p = less than 0.001) in blood pressure and converting enzyme activity and a rise in plasma renin activity. A slight but not significant rise in glomerular filtration rate and renal plasma flow without change in filtration fraction was observed. These data suggest that the renin angiotensin system is not involved in the glomerular hyperfiltration of Type 1 diabetes, and can be interpreted as showing no evidence for the presence of intraglomerular hypertension in these patients.

Contribution of the tissue angiotensin converting enzyme to the antihypertensive effect of altiopril calcium (MC-838) in spontaneously hypertensive rats

The effect of a new orally active angiotensin converting enzyme (ACE) inhibitor, calcium (-)-N-[(S)-3-[(N-cyclohexylcarbonyl-D-alanyl)thio]-2-methylpropionyl+ ++]-L- prolinate (MC-838, altiopril calcium), on systemic blood pressure (SBP) and tissue ACE activity has been examined in conscious spontaneously hypertensive rats (SHRs). MC-838 (3 mg kg-1) given orally to SHRs elicited a long-lasting hypotension lasting over 24 h. With the development of the hypotension, MC-838 significantly reduced ACE activity in the lung, kidney and aorta, but not in the brain and heart. Suppression of plasma ACE and rise of plasma renin activity occurred only transiently at an earlier stage.