POTASSIUM-CHLORIDE LOWERS BLOOD-PRESSURE AND CAUSES NATRIURESIS IN OLDER PATIENTS WITH HYPERTENSION

Epidemiologic surveys, experimental studies in animals, and clinical trials in young and middle-aged patients with hypertension indicate that dietary potassium lowers blood pressure. The mechanism of the antihypertensive effect is not well defined. Variations in serum potassium within the physiologic range may directly affect vascular smooth muscle tone. Potassium may also influence the regulation of blood pressure through effects on sodium handling, aldosterone secretion, the renin/angiotensin system, renal kallikrein, eicosanoids, and atrial natriuretic peptide. This study was undertaken to confirm the blood pressure-lowering effect of potassium in older patients and to determine the mechanism of the antihypertensive effect. Twenty-two patients greater-than-or-equal-to 60 yr of age were admitted to a Clinical Research Unit for 8 days after a 2-wk period free of antihypertensive medication. Patients were placed on an isocaloric diet containing 200 mmol/day of Na+, 70 mmol/day of K+, and 500 mg/day of Ca2+ and were treated in a randomized, double-blinded manner with either potassium chloride (120 mmol/day) or placebo. After 4 days, patients were crossed over to the alternate treatment. Systolic blood pressure decreased 8.6 mm Hg (95% confidence interval -14.6, -2.6), and diastolic blood pressure decreased 4.0 mm Hg (-6.9, -1.0) during potassium chloride supplementation. There was no significant change in blood pressure during treatment with placebo. Serum K+ was 3.9 +/- 0.1 mmol/L after 3 days of placebo and 4.3 +/- 0.1 after 4 days of potassium chloride (P < 0.002). Urinary sodium excretion averaged 192 +/- 11 mmol/day after placebo and 221 +/- 8 after potassium treatment (P < 0.02). Potassium treatment was not associated with changes in supine or captopril-stimulated PRA, GFR, atrial natriuretic peptide level, or urinary excretion of thromboxane B2 or 6-keto-prostaglandin F1-alpha. It was concluded that potassium chloride lowers blood pressure and increased sodium excretion in older patients with mild hypertension. The blood pressure effect may be due in part to potassium-induced natriuresis.