Effect of Sodium Balance on Arterial Blood Pressure and Renal Responses to Prostaglandin A 1 in Man

Abstract

The effect of sodium balance on systemic arterial blood pressure and the renal response to intravenous infusion of prostaglandin A₁ (PGA₁) was studied in hypertensive subjects. PGA₁ (0.4 µg/kg min^-1) was infused for 1 hour in ten hypertensive subjects who were receiving a constant diet containing 40 mEq of sodium and 80 mEq of potassium. During PGA₁ infusion a significant fall in both systolic and diastolic arterial blood pressure occurred. There was a significant rise in urine flow rate, renal plasma flow, and urine sodium excretion; plasma renin activity (PRA) rose slightly but not significantly. Eight of the ten subjects and one additional subject were then placed on furosemide (80 mg/day) for 1 week. In all subjects, a significant weight loss and a rise in midday PRA occurred with the administration of the diuretic. Systolic blood pressure fell, but diastolic pressure was unchanged. Following salt depletion with furosemide, PGA₁ infusion studies were repeated. PGA₁ then produced no significant change in systolic or diastolic blood pressure. Urine flow, renal plasma flow, and urine sodium excretion rose, but the degree of increase was markedly less than that observed prior to furosemide administration. In the salt-depleted subjects, a significant rise in PRA occurred during PGA₁ infusion. The results indicate that volume depletion diminishes the systemic and renal hemodynamic response to infused PGA₁ but enhances the PRA response. The increased PRA response during PGA₁ infusion observed in saltdepleted subjects might in part account for the blunted hemodynamic changes. Alternatively, recent evidence indicates that the enhanced production of endogenous vasodilating prostaglandins which occurs in the salt-depleted state might account for the diminished hemodynamic responses to exogenous PGA₁.