Renin, aldosterone, and serum-converting enzyme activity during normal and hypertensive pregnancy.

Plasma renin activity, plasma aldosterone, and serum-converting enzyme activity were measured in 13 normotensive pregnant women in three sequential periods: 19-21, 29-31, and 38-40 weeks of gestation. The converting enzyme activity was also measured in a group of 6 women with hypertensive pregnancy and an age-matched control group of 35 normal nonpregnant women. Plasma renin activity and plasma aldosterone values were both significantly elevated in the three periods of pregnancy, but plasma aldosterone levels were relatively lower during the first two periods. This is suggested to be secondary to depressed aldosterone secretion by intravascular volume expansion. The serum-converting enzyme activity did not change during pregnancy, and the mean values (1.02 +/- 0.27 U) were lower than those found in the control group (1.23 +/- 0.26 U). Similar low values were found in the hypertensive pregnancy group (1.11 +/- 0.35 U). Therefore, we assume that the converting enzyme is not a limiting factor in the conversion of angiotensin nor does it contribute significantly to the pathogenesis of hypertensive pregnancy.