Roles of Basal Levels of Circulating Luteinizing Hormone on Follicular Maturation in the Pregnant Golden Hamster (Mesocricetus auratus).

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To investigate physiological roles of basal levels of circulating LH on follicular development during the second half of pregnancy in golden hamsters, we treated animals with anti-luteinizing hormone (A/LH) or normal horse serum (control serum) at 1100 h on day 12 of pregnancy (day 0 of pregnancy=sperm positive in vaginal smear). Thereafter, changes in plasma concentrations of immunoreactive (ir)-inhibin, estradiol-17β, progesterone and testosterone were determined until 48 h after the treatment; ovaries were also examined immunohistochemically. Furthermore, pregnant golden hamsters were injected with human chorionic gonadotropin (hCG) to determine the effects of immunoneutralization of LH on follicular activity. Plasma concentrations of ir-inhibin and estradiol-17β decreased significantly within 24 h after A/LH treatment, while plasma concentrations of progesterone and testosterone were unchanged. The number of follicles ovulating in response to hCG in the A/LH treated groups (7.0 ± 3.4, n=3) was significantly lower than in the control serum treated group (34.6 ± 4.8, n=5) at 24 h after the treatment. Immunostaining of inhibin α subunit was observed in granulosa cells of healthy and atretic large follicles at 24 h after A/LH treatment, whereas immunopositive reaction of aromatase was not observed in atretic follicles. Positive immunoreaction of 17α-hydroxylase/C17, 20-lyase (CYP17) was observed in theca cells of healthy follicles but not in atretic follicles. These results clearly demonstrate that basal levels of circulating LH are important for maturation of antral follicles and secretion of ir-inhibin and estradiol-17β, but not for progesterone during the second half of pregnancy in the golden hamster.