ALDOSTERONE RESPONSES TO HYPERKALEMIA IN HEALTHY ELDERLY HUMANS

Plasma aldosterone levels are reported to be lower in healthy elderly individuals compared with young individuals, a difference exaggerated by sodium depletion or upright posture. The aim of this study was to d etermine the aldosterone response to increases in serum potassium with advancing age. In the Clinical Research Center, six healthy young (20 to 35 yr of age) and six healthy elderly (65 to 85 yr of age) subject s underwent evaluation of their aldosterone responses to potassium inf usion (0.5 mEq/kg over 45 min). Both young and elderly subjects had si milar basal serum potassium levels (4.3 +/- 0.2 versus 4.4 +/- 0.1 mEq /L), similar sodium and potassium excretion amounts and similar increa se in serum potassium levels during infusion (to 5.0 +/- 0.2 versus 5. 1 +/- 0.1 mEq/L). However, elderly subjects had lower basal levels of plasma aldosterone and a blunted aldosterone response to potassium inf usion (P < 0.05, analysis of variance). Advancing age is characterized by relative hypoaldosteronism in the basal state as well as in respon se to hyperkalemia. This may contribute to an increased susceptibility to hyperkalemia if other potassium regulatory systems fail.