Study of the effects of cicletanine on the renin-angiotensin-aldosterone system.

The effect of a single dose of 50 mg of cicletanine on plasma renin activity, plasma potassium and aldosterone, blood pressure, urinary volume and sodium and potassium excretion was compared to the effect of the same dose given for 9 days in eight normal volunteers in metabolic balance on 120-140 mEq of sodium and 50-70 mEq potassium. Following 4 days of this standardized diet, the normal volunteers received their first dose of cicletanine after an overnight fast and blood was collected at 30 min, 2, 4 and 6 h for plasma renin activity and aldosterone. Urine excreted following a modest water load was also collected and analysed over a 6-h period. Following the single dose there was an increase in PRA at 1 and 2 h, while there was no such increase with chronic administration. Plasma aldosterone, however, showed no difference between acute and chronic administration of cicletanine treatment. Also plasma uric acid levels increased with acute but not chronic cicletanine. There were no differences in heart rate and blood pressure responses, nor in urine volume, urinary sodium or potassium excretion, or plasma potassium between the different treatments. This study strongly suggests that the antihypertensive effect of cicletanine is not the result of an increased diuresis, as in this case enhanced urinary electrolyte excretion and increased plasma renin activity and aldosterone would be mandatory following chronic administration. Recent evidence suggests that the dissociation between plasma renin activity and aldosterone is the consequence of an effect of cicletanine on intracellular calcium mobilization. This mode of action would explain both the antihypertensive as well as the aldosterone secretion reducing effect of cicletanine.