The Metabolism and Secretion of Aldosterone in Elderly Subjects

The secretion rates [34 +/- 6 (SE) mug per day, 9 subjects] and metabolic clearance rates (MCR) [1,288 +/- 120 (SE) L of plasma per day, 9 subjects] of aldosterone in elderly subjects are significantly lower than those of young subjects [77 +/- 7 (SE) mug per day and 1,631 +/- 106 (SE) L per day, respectively]. There is a correlation of the MCR and secretion rate values (p = 0.02), but the calculated plasma concentrations (secretion rate/MCR) are also significantly low in the elderly subjects [2.6 +/- 0.3 (SE) compared with concentrations in the plasma from young subjects of 4.7 +/- 0.6 (SE) mug per 100 ml plasma]. The urinary excretion of radioactivity from oral and intravenously administered labeled aldosterone as aldosterone in the neutral extract, as aldosterone released by acid hydrolysis, and as tetrahydroaldosterone released by incubation with beta-glucuronidase is generally similar for young and elderly subjects except that a larger portion of the oral compared with the intravenous dose is excreted as free aldosterone in the elderly subjects, indicating that the splanchnic extraction is reduced. The calculated splanchnic blood flow (assuming no alteration in extrasplanchnic metabolism) is also slightly lowered. Therefore, as in patients with mild cardiac dysfunction, the lowered MCR of subjects is due to both reduced splanchnic extraction and blood flow. However, unlike the heart failure patients, in the elderly subjects the plasma concentration of aldosterone is also reduced.