Marked elevation of plasma renin activity during post diuretic sodium conservation in furosemide stimulated subjects

Plasma renin activity (PRA) was measured in 3 subjects during control period, after 3 days of oral furosemide (40 mg B.I.D.) and on the 2nd, 3rd and 5th days post diuresis. PRA, ng of angiotensin per ml plasma per 3-hour incubation was 8, 0.4 ng during the control period and rose to 51, 6 and 16 respectively. During the post diuretic phase, PRA rose to 99 in the first and 49 in the second subject. Urinary sodium was drastically reduced during this period. By 5th post diuretic day PRA returned to normal values. Striking elevations of PRA during intense sodium conservation are in accord with a concept of reduced Na load to macula densa stimulating renin release.