Estradiol-induced luteal regression in the rhesus monkey: evidence for an extraovarian site of action.

Studies were performed to test the hypothesis that estradiol is a physiologic luteolysin in the rhesus monkey and that it acts within the ovary containing the corpus luteum. Samples of peripheral blood were collected every 4 h and analyzed for various reproductive hormones to provide an index of the pattern of estradiol produced just before and during luteal regression, as monitored by serum progesterone concentration. After ovulation, serum estradiol rose to a midluteal phase plateau of 30–40 pg/ml, then rose again to nearly 70 pg/ml in the late luteal phase. The second increase in estradiol occurred after progesterone had begun to decline, suggesting that this latter rise does not initiate luteolysis. Evidence that the midluteal phase plateau in circulating estradiol might contribute to luteolysis was provided by the response to exogenous estradiol administered via small Silastic implants. Premature luteolysis was induced in 7 of 12 monkeys by sustained intraluteal delivery of a dose of estradiol which ...