The effects of an LH-RH antagonist ([N-Ac-D-Trp(1)(3), D-p-Cl-Phe(2), D-Phe(6), D-Ala(10)]-LH-RH) during the preovulatory period of the rhesus monkey.

Seven regularly cycling rhesus monkeys (Macaca mulatta) were used in this experiment. The animals were followed during two consecutive cycles. During the first cycle (control), the animals did not receive any treatment and the date of ovulation was determined by using daily total serum estrogens and serial laparoscopies. In the second cycle, the animals received 1 mg daily of [N-Ac-D-Trp(1)(3),D-p-Cl-Phe(2), D-Phe(6), D-Ala(10)-LH-RH by intramuscular injection from days 10-14. The date of ovulation was determined by using the same methodology as the control cycle. Blood samples were drawn daily from day 8 of the cycle until the onset of menses, and the serum was used to measure total estrogens, progesterone and LH. A significant delay of the preovulatory LH peak and ovulation occurred in 5 of the 7 animals resulting in a proportional increase in cycle length as compared to the control cycle. No changes in cycle length or date of LH peak occurred in the other 2 animals. One of them did not present signs of ovulation as determined by laparoscopy (no recognizable stigma or corpus luteum). Progesterone production and length of the luteal phase were not affected by the treatment.