Relation between the hypotensive and renin-suppressing activities of alpha methyldopa in hypertensive patients

In hypertensive patients with normal or low renin levels the possibility was explored that the hypotensive action of alpha methyldopa is dependent on the renin-suppressing effect. All observations argued against this possibility: (1) Comparison in the same patients of the effects of propranolol and alpha methyldopa showed that alpha methyldopa caused less effective reduction of renin although it was clearly more powerful than the beta adrenergic blocking agent in decreasing blood pressure. (2) No correlation was found between the hypotensive and the renin-suppressing effects of alpha methyldopa or between the hypotensive response and plasma renin activity before treatment. (3) When the effects of two different doses of alpha methyldopa were compared, the smaller dose (500 mg/day) was found almost as active as the larger one (1,000 mg/day) in suppressing renin although the larger dose was twice as powerful as the smaller one in reducing blood pressure. (4) Finally, no significant difference was observed in the hypotensive response to alpha methyldopa between hypertensive patients with normal or low renin levels. It is concluded that patients with essential hypertension and normal or low renin levels are responsive to the hypotensive action of alpha methyldopa and that this hypotensive action is not dependent on the simultaneous decrease in plasma renin activity.