The renin-aldosterone system in dihydralazine therapy during hypertensive pregnancy.

Ten patients with hypertensive pregnancy were studied in hospital for 3 weeks. Plasma renin activity (PRA), the daily urinary excretion of aldosterone (dU-Aldo) and electrolytes were studied before and during dihydralazine therapy (25 mg 3 times daily). In one week the supine blood pressure decreased (p less than 0.05) without any discernible tachycardia. PRA increased in 3 days of the treatment by 50% (p less than 0.05) and this mean level was maintained. In dU-Aldo no change was found, however, during the study; and the excretions of sodium and potassium remained unchanged as well. In patients without diuretic therapy the basal PRA level before dihydralazine therapy was lower than in normal pregnancy. Also, in patients with preceding diuretic therapy the basal level of PRA was lower than during diuretics in gravidas without hypertension. Judging from the animal experiments, the rise in PRA might be seen as favorable for uteroplacental circulation in pregnancy hypertension.