Physiological effects of short-term treatment with enalapril in hypertensive patients

To assess the effects of enalapril eight hospitalized hypertensive patients on constant sodium intake were treated with incremental doses of this angiotensin converting enzyme blocking drug. After four days of placebo treatment enalapril was given in single daily doses, starting with 1.25 mg and increasing until blood pressure was adequately controlled. On the 1.25 mg dose, angiotensin II (AII) and blood pressure did not change significantly, despite a 50% reduction in converting enzyme activity. There were, however, significant increases in noradrenaline, renin and aldosterone. With high doses a more pronounced reduction in converting enzyme activity was found while AII, aldosterone and blood pressure all fell significantly. Renin levels rose, but noradrenaline and adrenaline were reduced. Orthostatic hypotension did not occur. With continued treatment renal vascular resistance decreased concurrently with enhanced natriuresis and a reduction in body weight. Plasma volume rose slightly. The data indicate that enalapril may lower blood pressure by converting enzyme inhibition, but sodium loss and a decrease in sympathetic activity are associated features.