AGE-RELATED CHANGE IN PLASMA-ALDOSTERONE RESPONSE TO EXOGENOUS ANGIOTENSIN-II IN THE RAT

Age-related changes in aldosterone response of the adrenal cortex to e xogenous angiotensin II were studied in old compared to adult Long-Eva ns female rats. All animals were pretreated with dexamethasone and cap topril and anesthetized with pentobarbital. Continous infusion of angi otensin II (20 and 300 ng/min per 100 g body weight) for 20 and 30 min markedly enhanced the plasma concentration of aldosterone; however, t he plasma aldosterone incremental response was significantly lower (-6 6.8% after the highest dose of angiotensin II) in old than in adult ra ts. These results, the first in the rat, suggest that the previously r eported diminished aldosterone secretion is, at least in part, due to an impaired aldosterone biosynthesis capacity of the adrenal glomerula r cells in response to angiotensin II.