Effect of a 48-hour intravenous delta 4-androstenedione infusion on the pregnant rhesus monkey in the last third of gestation: changes in maternal plasma estradiol concentrations and myometrial contractility.

Increased myometrial activity in the pregnant rhesus monkey occurs in situations in which plasma estrogen concentrations are elevated. Examples of such situations are after laparotomy, with or without hysterotomy, and before delivery. The increased activity occurs primarily in the hours of darkness. To investigate the possibility of a causal relationship between the rise in estrogens and myometrial activity, we infused androstenedione intravenously for 48 hours to the rhesus monkey in the last third of gestation. Myometrial activity was quantified either as an increase in the number of individual contraction events or as a change in the power spectrum at high frequencies characteristic of contractions. Androstenedione infusion was followed by increased myometrial activity. Maternal plasma 17 beta-estradiol concentration was significantly elevated at 10 AM on the second day of androstenedione infusion. We conclude that, in the rhesus monkey late in gestation, estradiol may play a role in the regulation of the contraction activity observed during the hours of darkness in several different situations.