Abstract. Plasma renin activity (PRA), urinary aldosterone excretion (dU-Aldo), urinary electrolytes (dU-Na, dU-K) and plasma progesterone were studied weekly in 22 women with twin pregnancies for three weeks whilst on salbutamol therapy (=8 mg three times daily) in hospital. Fifteen patients in this group were treated with diuretics for on an average six weeks and the therapy continued. All the patients except three were treated also with depot-formed oxyprogesterone during the study. As an additional control group ten twin pregnant women without any drug therapies were studied.
The mean level of PRA in twin pregnancy before betasympathomimetics was equal to that of the same phase (the 32nd week) of normal pregnancy. On the second day of the treatment the PRA levels was threefold (p <0.001) and later on twofold (p <0.05) when compared with the level before the treatment.
Before betasympathomimetics the mean level of dU-Aldo was in twin pregnancy already higher than in normal pregnancy (p <0.01). During the treatment dU-Aldo increased within a week (p <0.05-p <0.01) and a positive correlation between PRA and dU-Aldo was found (p <0.01). A decrease in dU-Na and an increase in dU-K were found (p <0.05), corresponding to the increased effect of aldosterone. The increased levels of progesterone and aldosterone in twin pregnancy agree with earlier suggestions concerning the importance of progesterone in the secretion of aldosterone during pregnancy. The stimulating effect of betasympathomimetics, however, leads to a renin-mediated secondary aldosteronism and therefore tend also to cause hypokalemia.