Plasma and urinary aldosterone and their interrelations with blood pressure, plasma renin activity and urinary electrolytes in normotensive subjects

Plasma aldosterone (PA), urinary aldosterone excretion (Aldo-U), urinary sodium and potassium excretion and supine and sitting blood pressure (BP) were studied in 120 normotensive subjects. PA was determined after 1 h supine rest (basal PA), after ambulation for 3-4 h (upright PA) and after stimulation with 80 mg frusemide orally (stimulated PA). Aldo-U and urinary electrolytes were measured the day before the PA determinations. PA and Aldo-U were determined by specific radioimmunoassays. Basal PA rose approximately twofold after upright posture and about three-fold after frusemide stimulation. However, there was a very wide scatter in PA values between individual subjects. A significant correlation existed between basal PA and Aldo-U (r = 0.42, P < 0.001). Aldo-U decreased with increasing age. The PA values correlated fairly well with the concomitant values for plasma renin activity (r = 0.26-0.40, P< 0.004 for basal PRA and P< 0.001 for both upright and stimulated PRA). No relationships could be found between Aldo-U and urinary electrolyte excretions. No correlations were observed between aldosterone and BP.