A role for estrogen in progesterone production during baboon pregnancy.

The present study determined whether estrogen is important in the production of progesterone (P) during primate pregnancy. Serum P production rates (metabolic clearance rate [MCR] x peripheral serum concentration) were determined in baboons prior to and following maternal administration of the antiestrogen ethamoxytriphetol (MER-25) at 30, 15, 6, or 3 mg/kg of body weight by mouth daily for 10 or 20 day periods during or throughout the last one third of gestation. Maternal peripheral serum P concentrations decreased (p less than 0.05 to P less than 0.001, t test) 37 to 60% in 7 of 9 baboons following daily administration of MER-25. Since mean MCR-P prior to (1,567 1/day) and following (1,361 1/day) MER-25 were similar, the decline in serum P concentration reflected decreased P production. Serum P concentrations in five untreated baboons during the last one third of gestation fluctuated in level, but no significant sequential rise or fall occurred. The decrease in P production in baboons following antiestrogen administration suggests that the action of estrogen is required for sustaining the elevated P production typical of baboon pregnancy.