Effect of chlorthiazide treatment on renin-aldosterone system during pregnancy.

Plasma renin activity and urinary excretions of aldosterone, sodium and potassium were studied before and during one week's chlorthiazide treatment in eight women with a slight peripheral oedema in the 31st week of pregnancy. Plasma renin activity and excretion of aldosterone increased clearly on the first day of treatment, but on the 7th day it was more than doubled in comparison with the level before the treatment. Diuresis and excretion of sodium increased promptly on the 1st day, but did not differ from the level found before the treatment on the 7th day. The high reserves of renin and aldosterone secretion found in this study may be regarded important in ensuring blood pressure, plasma volume and placental flow during pregnancy.