Morton Jj

Enalapril in the treatment of hypertension with renal artery stenosis.

The converting enzyme inhibitor enalapril, in single daily doses of 10-40 mg, was given to 20 hypertensive patients with renal artery stenosis. The blood pressure fall six hours after the first dose of enalapril was significantly related to the pretreatment plasma concentrations of active renin and angiotensin II and to the concurrent fall in angiotensin II. Blood pressure fell further with continued treatment; the long term fall was not significantly related to pretreatment plasma renin or angiotensin II concentrations. At three months, 24 hours after the last dose of enalapril, blood pressure, plasma angiotensin II, and converting enzyme activity remained low and active renin and angiotensin I high; six hours after dosing, angiotensin II had, however, fallen further. The rise in active renin during long term treatment was proportionally greater than the rise in angiotensin I; this probably reflects the fall in renin substrate that occurs with converting enzyme inhibition. Enalapril alone caused reduction in exchangeable sodium, with distinct increases in serum potassium, creatinine, and urea. Enalapril was well tolerated and controlled hypertension effectively long term; only two of the 20 patients required concomitant diuretic treatment.

A STUDY OF THE RENIN INHIBITOR H142 IN MAN

The inhibitor of human renin, H142, was studied in nine male volunteers. On three occasions, in random order, volunteers were infused with 5% dextrose or with H142 at 1.0 or 2.5 mg/kg per h for 30 min while supine and thereafter with dextrose for 1 1/2 h. There was a marked reduction in plasma active renin concentration as assayed by an enzyme-kinetic method, with parallel falls in the circulating concentrations of angiotensins (ANG) I and II, all of which rebounded transiently to values above basal after the H142 infusion was stopped. In contrast, total renin concentration as measured by radio-immunoassay rose while ANG I and II fell, subsiding when H142 was discontinued. There was a slight but significant increase in plasma noradrenaline as renin became inhibited; plasma adrenaline was unchanged. H142 produced a slight fall in systolic blood pressure (SBP) and a clearer, highly significant, dose-related fall in diastolic blood pressure (DBP). There was a modest but significant increase in the heart rate. These studies confirm H142 as an effective inhibitor of human renin in vivo.

Effects of prolonged and brief infusions of noradrenaline on arterial pressure and on the plasma concentrations of active renin, angiotensin II, aldosterone and potassium.

Conscious male beagle dogs were given constant intravenous infusions of noradrenaline for 14 days, four receiving 125 ng/kg/min and four 250 ng/kg/min. Before, during and after these infusions dose-response studies were done in which additional noradrenaline was infused at 500, 1000 and 2000 ng/kg/min, each rate for 1 h. Blood samples were taken before and during infusions for measurement of haematocrit and plasma concentrations of noradrenaline, active renin, angiotensin II, aldosterone, sodium and potassium. Fourteen-day infusion of noradrenaline at 125 ng/kg/min did not raise blood pressure significantly though infusion at 250 ng/kg/min did, but for the first week of infusion only. Heart rate decreased significantly at both rates. Arterial pressure fell markedly and significantly on stopping infusion. Mean plasma concentrations of renin, angiotensin II and aldosterone tended to be lower during prolonged infusion of noradrenaline, but only the fall of renin during the second week was significant in one group of dogs. Noradrenaline at higher rates significantly raised blood pressure and increased plasma concentrations of renin and angiotensin II. Plasma aldosterone concentration did not rise significantly, perhaps because plasma potassium concentration decreased; in support of this theory changes of plasma aldosterone correlated with changes of plasma potassium but not with changes of angiotensin II. The rise in arterial pressure during dose-response studies was related to the increase of plasma noradrenaline. Prolonged infusion of noradrenaline did not alter the dose-response relation between plasma noradrenaline concentration and arterial pressure.

Relation of blood pressure with body and plasma electrolytes in Conn's syndrome.

Thirty-four patients with untreated Conns syndrome were studied in a metabolic ward. The final diagnosis in each case was based on the finding and removal of an adrenal cortical adenoma with histological features typical of the disorder. Compared with 34 age and sex-matched normal controls the untreated patients had increased plasma aldosterone concentration, increased blood pressure (183/112 mmHg), increased exchangeable sodium (116.7% of normal), hypokalaemia and increased plasma sodium concentration. Exchangeable potassium was lower than normal and plasma concentrations of active renin, total renin and angiotensin II were lower than normal mean values. Arterial pressure correlated significantly and positively with plasma and exchangeable sodium and there was a significant negative correlation with plasma potassium concentration. Partial regression analysis showed that the relation of exchangeable sodium with blood pressure did not depend on age or renal function but that the relation of blood pressure and plasma potassium could be attributed to the correlation of exchangeable sodium and blood pressure. Multiple regression analysis suggested that exchangeable and plasma sodium were the most important determinants of blood pressure in untreated patients. Spironolactone, amiloride and surgical removal of the adenoma corrected the electrolyte abnormality and usually lowered blood pressure. The fall in exchangeable sodium was related to the fall in blood pressure. The pattern of correlation found by multiple regression analysis in postoperative patients was similar to that in normal subjects. The findings are relevant to some of the mechanisms proposed for the hypertension of mineralocorticoid excess.

New Inhibitors of Human Renin Tested in vitro and in vivo in the Anaesthetized Baboon

A new inhibitor of human renin (H. 189) is described. It is a decapeptide analogue of human renin substrate with the amino acid, statine, substituted for leucine in the scissile bond. Its inhibitory potency as shown by IC50 is 1.0 X 10(-8) M with human plasma renin and 1.5 X 10(-8) M with baboon plasma renin. It is less effective with dog and rat renin, but its inhibitory potency with human renin is similar to that of another inhibitor of ours (H. 142) having a reduced isostere in the scissile bond. H. 189 has some inhibitory effect on cathepsin D (IC50 6.5 X 10(-5) M) but H. 142 has no discernible effect. Pepstatin, on the other hand, was highly effective against cathepsin D (IC50 1.2 X 10(-8) M). H. 142 and H. 189 were infused intravenously at 10 mg/kg/h in four anaesthetized salt-deplete baboons (Papio hamadryas). The activity of renin in plasma decreased markedly as did the circulating concentration of its products, angiotensin I and angiotensin II.

Demeclocycline in the treatment of the syndrome of inappropriate antidiuretic hormone release: with measurement of plasma ADH.

A patient with the syndrome of inappropriate antidiuretic hormone release (SIADH) following head injury and meningitis was studied during treatment with demeclocycline, a drug known to produce a reversible nephrogenic diabetes insipidus. No changes were observed during six days of demeclocycline 1200 mg/24 hr but urine output increased significantly, with the production of a dilute urine, when the dose was increased to 2400 mg/24 hr. The patient lost weight, and all biochemical features of the syndrome were rapidly corrected despite an unchanged fluid intake and despite the persistence of high plasma levels of ADH. The rise in serum sodium was accompanied by mild sodium retention, as measured by external balance and exchangeable sodium. A complication of treatment was the development of acute renal failure possibly induced by a nephrotoxic effect of high circulating levels of demeclocyline. On stopping demeclocyline renal function returned to normal and, after some delay, SIADH returned, and was still present 9 months after initial presentation. This confirms earlier reports of the efficacy of demeclocycline in SIADH; but the authors advise caution against increasing the dose above 1200 mg/24 hr.

EFFECT OF THE ANGIOTENSIN II ANTAGONIST SARALASIN ON PLASMA ALDOSTERONE CONCENTRATION AND ON BLOOD PRESSURE BEFORE AND DURING SODIUM DEPLETION IN NORMAL SUBJECTS

The effect of the angiotensin II antagonist saralasin on plasma aldosterone, plasma angiotensin II and blood pressure was studied in six normal supine subjects both before and during sodium depletion. Before sodium depletion, infusion of saralasin produced no consistent changes; during sodium depletion, infusion of the angiotensin antagonist caused a fall in plasma aldosterone and an increase in plasma angiotensin II in each subject. It is concluded that angiotensin II plays a major part in stimulating aldosterone secretion during sodium depletion in man.

Factors Affecting Renal Vein Renin Ratio in Renal Artery Stenosis

All four factors which theoretically may affect the renal vein renin ratio in unilateral renal artery stenosis--increased renin secretion and diminished renal plasma flow on the stenotic side; suppressed renin secretion and renin extraction on the contralateral side--have been assessed. In a series of patients with unilateral renal artery stenosis, the renal vein ratio of active renin was more closely related to the reduction of renal plasma flow than to renin secretion rate on the affected side. On the contralateral side renin secretion was suppressed while angiotensin II was extracted. During long-term treatment with the converting enzyme inhibitor enalapril, peripheral plasma angiotensin II was lowered, while active renin concentration was markedly elevated, both in arterial plasma and in renal venous plasma of the stenotic kidney; the contralateral kidney became a net extractor of active renin. Thus, all 4 factors which theoretically affect the renal vein renin ratio can operate clinically. Both before and during enalapril, the affected kidney secreted inactive renin.

Effects of the renin inhibitor H77 on angiotensin II, arterial pressure and cardiac function in conscious dogs: comparison with captopril.

The renin inhibitor H77 and the angiotensin I converting enzyme (ACE) inhibitor captopril were compared in separate experiments with infusion of 5% dextrose as a control for the effects on plasma angiotensin II (Ang II) concentration, arterial pressure and cardiac function, measured by Swan-Ganz catheter, in conscious dogs. The effects of a high dose of H77 (10mg/kg perh) were similar to those of high-dose captopril (6mg/kg perh). Both reduced plasma Ang II concentration, systemic vascular resistance and arterial pressure; both increased the heart rate; both increased cardiac output but the change was significant only with captopril; neither affected stroke volume, pulmonary artery pressure or pulmonary vascular resistance; both reduced left and right atrial pressures. The similar pattern of effects for the two inhibitors suggests that the mechanism by which they act is the same — reduction in Ang II — and that the cardiovascular effects of H77 are not a specific action of the peptide that is unrelated to the reduction in plasma Ang II concentrations.

Inhibitors of rat renin and their use in experimental hypertension

Hydroxy-ethylene dipeptide analogues (Leu[CH(OH)-CH2]Leu and Leu[CH(OH)-CH2]Val) of human substrate peptides are potent in vitro inhibitors of rat renin with IC50 values as low as 0.8 nmol/l. When given to renal hypertensive rats they lower blood pressure and suppress both plasma renin and angiotensin II. There was a divergence between the rapid rebound of renin and blood pressure which remained suppressed.