Antiluteinizing Hormone: Acute Influence on Steroid and Gonadotropin Levels and Follicular Development in the Pregnant Hamster*

Abstract

Pregnant hamsters were injected at 0900 h on day 4 or 8 (day 1 of pregnancy = sperm-positive) with 0.1 ml of either normal horse serum (NHS) or equine antibovine LH (ALH) and decapitated 1, 3, 6, 12, 18, and 24 h later. Serum was saved for RIA of FSH, PRL, progesterone (P), testosterone (T), and estradiol (E2). Corpora lutea (CL) and nonluteal ovary (NLO) were saved for steroid determinations, and one ovary was saved for histology. Regardless of the day of treatment, ALH induced an immediate decline within 1 h in the serum and luteal E2 concentrations without altering T. At 24 h after ALH, levels of T and P in CL and sera were lower than NHS controls. In NLO, T and E2 declined simultaneously within 1 h after ALH without changing P. Within the next 3–6 h, P in NLO declined to half that of NHS pregnant controls and all antral follicles showed initial signs of atresia. Collectively, these results indicate that, after LH deprivation, the initial hormonal change is a concomitant decrease of E2 in serum, CL, andLO, suggesting that LH is necessary for E2 secretion and maintenance of antral follicles in the pregnant hamster and that decreases of P in serum, CL, and NLO lag behind changes in E2. A dramatic increase in serum FSH-like material accompanied the declines in serum P and E2 after ALH treatment, suggesting that lack of steroid negative feedback at the hypothalamicpituitary axis induces hypersecretion of FSH. A large dose of ALH (0.4 ml) induced a more prompt decline in serum P than 0.1 ml ALH, indicating that a greater degree of LH deprivation may occur sooner with 0.4 ml than with 0.1 ml ALH. Unlike the hysterectomized pseudopregnant (HSP) rat, ALH on day 8 of HSP in the hamster induced a terminal decline in serum P within 24 h. In contrast, the pregnant hamster on day 8 exhibited a more gradual decline in serum P than that observed in the HSP hamster, suggesting that placental factors may be exerting luteotropic actions at this time. The results indicate that luteal aromatizing enzymes appear highly sensitive to LH deprivation since, within 1 h after ALH, luteal E2 concentrations decline without a concomitant decrease in T.