Hormonal requirements for maintenance of follicular and luteal function in the hypophysectomized cyclic hamster

The amounts of luteinizing hormone (LH), follicle-stimulating hormone (FSH) and prolactin (Prl) required for follicular development or luteal maintenance were established by hypophysectomizing hamsters between 0900-1100 h of Day 1 of the cycle (=morning of ovulation) and injecting the animals s.c. over the next 4 days to stimulate the normal cycle. Animals were killed at 1300 h on Day 4 or injected with human chorionic gonadotropin (hCG) at 1500 h on Day 4 and killed the next morning to determine the ovulation rate. Daily injection of 20 IU hCG resulted in 8 antral follicles per ovary and ovulation of 12.4 ova, but 20 micrograms LH (in saline) failed to develop any antral follicles; 20 micrograms LH in polyvinylpyrrolidone (PVP) - which prolongs its biological activity - matured 2-4 antral follicles per ovary and the animals ovulated 3 ova in response to hCG. However, injection of 5 micrograms FSH on Day 1 plus 20 micrograms LH (in PVP) on Days 1-4 produced normal numbers of antral follicles and ovulation of 15 ova. When 5 micrograms FSH was injected daily along with LH (in PVP), follicular development was accentuated and the animals ovulated 49 ova. Keeping FSH constant at 5 micrograms/day and reducing LH from 20 micrograms to 10 or 5 micrograms per day did not reduce the number of follicles maturing or ovulating. Daily injection of Prl did not affect follicular development but maintained corpora lutea (CL) in some animals. Combined injection of Prl and LH (in PVP), but not FSH, maintained active CL in all animals. Thus, the hypophysectomized hamster requires tonically high levels of LH for the hormone to exert its follicular and luteal effects with FSH and Prl, respectively.