Luteal Function in Baboons with Administration of the Antiestrogen Ethamoxytriphetol (MER-25) Throughout the Luteal Phase of the Menstrual Cycle1

Abstract

Administration of the antiestrogen ethamoxytriphetol (MER-25) during late baboon gestation was reported to result in a marked decline in progesterone (P) production rate. Since both the placenta and corpus luteum appear to secrete P during late baboon gestation, this decline in P may reflect a loss in luteal and/or placental function. The effect of administration of the antiestrogen MER-25 upon serum steroid concentrations was determined during the luteal phase of the baboon menstrual cycle, a time when the source of P is almost exclusively the corpus luteum. Six baboons were bled throughout a control menstrual cycle and during daily administration (15 mg/kg body wt orally) of MER-25 throughout the luteal phase of the following cycle. Mean (.+-. SEM [standard error of the mean]) length of the luteal phase of the menstrual cycle was the same in baboons with no treatment (18 .+-. 0 days) and after MER-25 administration (18 .+-. 0 days). Mean (.+-. SEM) serum concentrations of P were similar in the luteal phase with no treatment (5.2 .+-. 0.7 ng/ml) and during MER-25 administration (5.0 .+-. 0.6 ng/ml). Serum P attained similar peak values of concentration in the luteal phase before and after antiestrogen administration and was detectable in the serum for a similar duration of the luteal phase of both cycles. Mean (.+-. SEM) serum concentrations of 17-hydroxyprogesterone which may also provide an index of luteal function, were similar in the luteal phase of the menstrual cycle in baboons with no treatment (0.53 .+-. 0.20 ng/ml) and during administration of MER-25 (0.42 .+-. 0.15 ng/ml). Serum estradiol (E2) concentrations attained a peak at midcycle, then declined to low values and MER-25 had no effect upon serum E2. Production of P by the corpus luteum, and thus the functional maintenance of the corpus luteum during the baboon menstrual cycle apparently is not influenced by the administration of antiestrogen. The decline in P production, previously shown in pregnant baboons given antiestrogen, thus may reflect a reduction in function of the placenta, but not the corpus luteum.