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 exogenous angiotensin II were studied in old compared to adult Long-Evans female rats. All animals were pretreated with dexamethasone and captopril and anesthetized with pentobarbital. Continuous infusion of angiotensin II (20 and 300 ng/min per 100 g body weight) for 20 and 30 min markedly enhanced the plasma concentration of aldosterone; however, the plasma aldosterone incremental response was significantly lower (-66.8% after the highest dose of angiotensin II) in old than in adult rats. These results, the first in the rat, suggest that the previously reported diminished aldosterone secretion is, at least in part, due to an impaired aldosterone biosynthesis capacity of the adrenal glomerular cells in response to angiotensin II.