Effect of pindolol on potassium homeostasis in patients with essential hypertension.

A study of the effects of pindolol on potassium homeostasis was undertaken in 25 patients (19 women, 6 men) with essential hypertension. The patients were maintained on their usual diet and were withdrawn from antihypertensive therapy for three weeks before the study began. They were then randomly assigned to one of three treatment groups: (a) pindolol, 15 mg daily; (b) hydrochlorothiazide, 50 mg daily; and (c) both drugs combined. Total body potassium (TBK), urine aldosterone excretion, and plasma renin activity (PRA) were measured after eight weeks of therapy and compared with pretreatment values. Mean PRA remained unchanged in patients taking only pindolol or the drug combination, but it rose significantly in patients taking only hydrochlorothiazide. Mean urine aldosterone concentrations fell in patients taking only pindolol, rose in those taking only hydrochlorothiazide, and remained unchanged in those taking the combination. Mean TBK concentrations rose significantly in patients taking only pindolol or the combination, and fell significantly in those taking only hydrochlorothiazide. The rise in TBK concentrations with the combination clearly suggests that pindolol offsets the potassium wastage induced by diuretics, though probably by a mechanism outside the renin-aldosterone system. Because of this rise, it may be possible to eliminate potassium supplementation in patients taking the combination pindolol and hydrochlorothiazide.