Luteal function following ovarian stimulation in rhesus monkeys for in vitro fertilization: Atypical response to human chorionic gonadotropin treatment simulating early pregnancy

This study determined if corpora lutea of hyperstimulated cycles in rhesus monkeys could be 'rescued' by the pregnancy signal, chorionic gonadotropin (CG), given at the typical time of implantation. At menses, female monkeys received human follicle-stimulating hormone (hFSH, 60 IU, days 1 to 6) followed by human menopausal gonadotropin (hMG, 60 IU hFSH/60 IU luteinizing hormone [hLH], days 7 to 9). On day 10, human chorionic gonadotropin (hCG) was given to mimic the LH surge. Nine days later, a regimen of daily increasing doses of hCG (15 to 360 IU twice a day) was initiated to simulate rescue of the corpus luteum in early pregnancy. Serum levels of progesterone (P) increased through day 5 of the luteal phase but then declined. Circulating levels of bioactive LH were signficantly less on days 7 to 9 of the luteal phase than at this stage in the natural cycle. The hCG regimen extended (P < 0.05) the luteal phase in five of six animals. The hCG treatment elicited a persistent increase (P < 0.05) in circulating P levels, rather than a transient rise typical of normal or simulated pregnancy in natural cycles. The authors conclude that (1) corpora lutea of hyperstimulated cycles can respond to CG, but (2) there are differences in luteal function during both the luteal phase and simulated early pregnancy that may be due to inadequate luteal development or the abnormal gonadotropin milieu existing after ovulation or both.