Progesterone and 5 alpha-pregnane-3,20-dione in serum of peripartum rhesus monkeys.

Abstract

To determine whether there are qualitative or quantitative changes in placental steroidogenesis related to the time of day and onset of parturition in the rhesus monkey, systemic venous levels of progesterone (P) and 5α-pregnane- 3,20-dione (DHP) were measured by RIA at 0900 and 2100 h pre- and postpartum. To establish that these steroids were in fact secreted from the uterus and/or its contents, their concentrations were also determined at various stages of pregnancy in peripheral and uterine venous sera obtained during laparotomy. Throughout gestation, P and DHP were secreted from the uterus and/or its contents, as indicated by higher steroid levels in uterine than femoral veins. In prepartum monkeys, peripheral P and DHP concentrations were higher at 2100 than at 0900 h (P < 0.001), and in those animals sampled twice daily up to and including the day of parturition, P and DHP levels at 0900 h averaged 2.4 and 0.26 ng/ml, respectively, while at 2100 h, P and DHP were 5.9 and 0.61 ng/ml, respectively. No major variations in steroid levels were noted before parturition during the morning or evening. In two postpartum lactating monkeys in which peripheral steroids were measured twice daily, no significant morning-evening differences were noted. Since corpora lutea in these animals reportedly continue to secrete progestins, the nocturnal increase in steroid levels found prepartum may reflect an alteration in placental steroid secretion. However, the possible cause or significance of this increase and its relationship to parturition remain to be established.