The influence of age on renal function and renin and aldosterone responses to sodium-volume expansion and contraction in normotensive and mildly hypertensive humans.

To determine the effects of age on the responses of renin, aldosterone (PA), sodium excretion, and renal function to provocative maneuvers, we performed volume expansion and contraction in 390 normotensive and 212 hypertensive subjects in the second to seventh decades of life. The subjects were classified as Na-sensitive if their mean blood pressure was 10 mm Hg or more higher after volume expansion than volume contraction. Sodium sensitivity was associated with hypertension and increasing age. Plasma renin activity decreased with age under basal, stimulated, and suppressed conditions; the decrease was greater in hypertensives than in normotensive persons. The PA values were greater in hypertensives than in normal subjects after volume expansion. There was an age-related decrease in PA values after volume contraction in normal, but not in hypertensive, persons. With volume expansion, hypertensive persons exhibited "exaggerated natriuresis." There was an age-related increase in natriuresis in both groups; the increase was greater in hypertensives than normal subjects. Creatinine clearance decreased with age; however, the rate of decrease in this cross-sectional study was not different in hypertensive and normotensive subjects. These observations may have a bearing on why NaCl affects the blood pressures of older individuals more than younger persons.