Effect of spironolactone treatment on the renin-aldosterone system during pregnancy.

Ten pregnant patients were treated with spironolactone (100 mg daily) for two weeks. The patients were on a continuous long-term saluretic therapy for pregnancy edema. In addition, a potassium supplementation (30 mmol/day) was given until the beginning of spironolactone treatment. The patients thus treated had a mean urinary aldosterone excretion (dU-Aldo) of more than ten-fold in comparison to that of non pregnant state. Canrenone, the effective conversion product of spironolactone in plasma, reached its steady state level in three days as in non-pregnant subjects. dU-Aldo decreased in two weeks during the spironolactone by 36% (p less than 0.05). The inhibition of aldosterone secretion is thus evident also after a low clinical dose of spironolactone. Urinary potassium excretion (dU-K) decreased during the 1st day (p less than 0.05) and continued to decrease during one week of spironolactone therapy by a total of 21% (p less than 0.001). The decrease in dU-K reflects the cessation of potassium supplements in the beginning of the study. No changes in urinary sodium excretion were found. Plasma renin activity (PRA) increased in one week by 79 per cent and the changes of PRA and dU-Aldo showed inverse correlation (p less than 0.001). In our study natriuresis, cannot explain the increase of PRA. Our study suggests another feedback effect of aldosterone.