Renin-aldosterone system and urinary electrolytes after amiloride, hydrochlorothiazide and the combination.

Plasma renin activity (PRA), urinary aldosterone excretion (U-Ald) and electrolyte excretions were studied after a placebo (P) (n = 47) and during the following day randomly after amiloride (A) (5 mg, n = 18), hydrochlorothiazide (H) (50 mg, n = 12) and hydrochlorothiazide + amiloride tablets (HA) (50 + 5 mg, n = 19). After A no change in PRA or in U-Ald could be found in 24 hr. After H an increase in PRA was found, but not until 24 hr, and U-Ald was increased during 8--24 hr. HA possessed a higher saluretic effect than H, but the excretion of potassium was lower. PRA increased in 8 hr after HA and a further increase was seen until 24 hr. U-Ald had already increased after HA during 0--8 hr, and U-ALD was higher during 8--24 hr and 0--24 hr than after H. After HA a positive correlation was found between the increases of sodium excretion and PRA; between U-Ald and PRA a positive correlation was also found; but between potassium excretion and PRA or U-Ald there was no correlation. The results suggest the priority of natriuresis in the regulation of renin release after H and HA. The stronger reaction of the renin-aldosterone system after HA than after H thus may result from the faster and higher natriuretic potency of this combination in acute study.