EFFECT OF AGING ON RENIN-ACTIVITY AND ALDOSTERONE EXCRETION

Abstract

Twenty or more normal subjects (half males) in each decade of life from age 20-80 yr were included in the study. Plasma renin activity (PRA) was measured with the subjects on a normal Na diet and after Na restriction and standing. Aldosterone and Na excretion rate was measured on unrestricted Na intake and on day 3 of Na restriction. Plasma renin activity was quantitated by both bioassay and radioimmunoassay of angiotensin-I. Plasma renin activity under both test conditions declined with increasing age, especially those over 40. Values of those in the 7th decade averaged 60% of the value of that of the younger age group. Response of renin activity to Na restriction and standing was 73% of that of the younger age group. Older females were less responsive to Na restriction and standing. Aldosterone excretion rate declined with increasing age, so that by the 7th decade the values averaged 55% of those in the 2nd decade of life. Aldosterone excretion rate in response to Na restriction also declined with increasing age, particularly above the 4th decade, so that the values on day 3 of Na restriction in the older subjects averaged 33% of that of the subjects in the 2nd decade of life. Renin substrate did not decline with increasing age. The decline in renin activity and aldosterone values in the older subjects appeared to be due to factors other than Na or K intake.