Acute Natriuresis Induced by Inhibition of Proximal Tubular Reabsorption of Sodium and Water in Hypertensives Following Acute Calcium Entry Blockade with Nifedipine

Abstract

To elucidate the renal effects and especially the natriuretic properties of calcium entry blockers, we studied the effect of sublingual nifedipine 20 mg in 16 patients with mild to moderate essential hypertension. The lithium clearance technique was utilized and constant infusion technique was employed to measure glomerular filtration rate (GFR) and renal plasma flow (RPF). Nifedipine induced a significant reduction of systolic and diastolic blood pressure and an increase in heart rate. RPF increased and renal vascular resistance fell significantly, whereas GFR was unchanged. A significant increase in diuresis and in clearance of sodium and lithium was seen. The absolute and fractional proximal reabsorption of sodium and water was reduced. The absolute distal reabsorption increased significantly. The results indicate that the natriuretic action of nifedipine in hypertensives is a proximal tubular event.