The Role of Renin in the Exaggerated Natriuresis of Hypertension

Hypertensive patients were classified according to their plasma renin response when challenged by the potent diuretics, ethacrynic acid (50 mg IV), or furosemide (40 mg IV), into renin-unresponsive and renin-responsive groups. In the latter plasma renin activity rose by at least 0.5 ng of angiotensin/ml/hr after the diuretic. The response to volume expansion with 2 L of isotonic saline infused over 60 min was then studied. Peak rate of sodium excretion after saline loading was 994±186 &mgr;Eq/min in the renin-unresponsive group and peak urine flow was 11.9 ± 2.1 ml/min. In the renin-responsive hypertensives peak sodium excretion was 448 ± 149 &mgr;Eq/min and peak urine flow was 5.4 ± 1.5 ml/min. Both the sodium excretion and urine flow responses were significantly higher (P < 0.05) in the renin-unresponsive group. The degree of saline-induced diuresis and natriuresis was not related to the preexisting level of aldosterone production. Plasma renin changed little in either group during saline infusion but tended to be higher at all times in the renin-responsive subjects. The enhanced capacity of the renin-unresponsive hypertensive subjects to excrete a salt load suggests either a functionally significant degree of extracellular fluid volume expansion or a direct role for renin in the natriuresis accompanying volume expansion.