Suppression of postovulatory gonadotropin levels does not affect corpus luteum function in rhesus monkeys

The exact mechanism(s) of control of corpus luteum function remains unknown. To address the question whether luteinizing hormone (LH) plays an important role, the following experiments were performed in cycling rhesus monkeys. Experiment 1: 10 monkeys were followed for 2 consecutive cycles and ovulation data determined using serum estradiol (E2) measurements and serial laparoscopies. In the second cycle, starting on day 1 after ovulation, the animals received daily administration of a potent inhibitory LHRH analog, [N-Ac-D-Trp1,3,D-p-Cl-Phe1,D-Phe6,D-Ala10]-LH-RH (N = 5) or vehicle (N = 5) until the onset of vaginal bleeding. Serum FSH and LH concentrations declined significantly in animals treated with the antagonist. However, E2 and progesterone (P) levels were not different from vehicle-treated monkeys. Luteal phase length in both groups was unchanged from the control cycle. Experiment 2: the same protocol was followed, adding the administration of hCG in increasing dosages from days 6-10 after ovulation (Day 6 = 30 IU, Day 7 = 60 IU, Day 8 = 90 IU, Day 9 = 180 IU, Day 10 = 360 IU). The increase in serum P concentration was the same for both groups. These results suggest that significant suppression on gonadotropin levels after ovulation does not affect corpus luteum function and that the inhibitory analog does not have a direct effect on the ovary.