Hamsters were hypophysectomized on day 4 of pregnancy (day 1 = sperm in vaginal smear) and injected subcutaneously on days 4-7 with various combinations of 200 micrograms prolactin (Prl), 10 micrograms follicle-stimulating hormone (FSH), and 20 micrograms luteinizing hormone (LH) in polyvinylpyrrolidone (PVP) to decrease its rate of absorption or in saline. End points for luteal function on day 8 were maintenance of pregnancy, serum progesterone (P4), luteal weight, and luteal binding for human chorionic gonadotropin, FSH, and Prl. After hypophysectomy, a drastic decline occurred in all parameters including an 89% decrease in luteal weight. Injection of Prl did not maintain pregnancy nor serum P4 but partially maintained luteal weight and human chorionic gonadotropin binding sites per corpus luteum. The minimal luteotropic complex of Prl and FSH was effective in maintaining pregnancy and significantly increased serum P4 and Prl and FSH receptors but not to control levels; Prl and LH (PVP) was also effective to the same extent. Antral follicles were lacking after either treatment. The effects of FSH cannot be attributed to LH contamination. All variables were restored to control levels by Prl plus FSH plus LH (PVP) and antral follicles were present; Prl plus FSH plus LH (saline), however, induced luteolysis and reduced most values to the levels found in untreated, hypophysectomized animals. Thus, the luteotropic activity of LH was only demonstrable when it was injected in a long-acting form; when delivered as a bolus, LH (saline) was luteolytic.
Role of the β93-100 Determinant Loop Sequence in Receptor Binding and Biological Activity of Human Luteinizing Hormone and Chorionic Gonadotropin
