Effect of Hypophysectomy on Atresia of Rat Preovulatory Follicles1

Abstract

Atresia of Graafian follicles was induced by hypophysectomy on the morning of the day of proestrus. As early as 6 h after hypophysectomy, follicles showed a reduced ability to respond with ovulation to administration of hCG, and 12 h after hypophysectomy all the follicles failed to ovulate. At 24 h after hypophysectomy, the follicles exhibited morphological changes characteristic of early atresia followed by advanced atresia at 48 h after the operation. Steroidogenesis in vitro of follicles from hypophysectomized rats was compared with that of sham-operated controls. The mean ± SEM rate of accumulation (ng/follicle/24 h) of progesterone, testosterone, and estradiol-17β was 5.1 ± 0.9, 6.3 ± 0.5, and 20.2 ± 3.7, respectively, in control follicles; 12 h after hypophysectomy progesterone accumulation was 22.7 ± 4.9, testosterone 4.5 ± 0.4, and estradiol-17β 11.7 ± 0.9; and 48 h after the operation accumulation was 59.3 ± 8.3, 1.0 ± 0.3, and 0.10 ± 0.02, respectively. Thus atretic follicles from hypophysectomized rats are characterized by increased progesterone and decreased androgen and estradiol-17β production. Addition of LH to the culture medium stimulated progesterone accumulation in follicles from rats up to 24 h after hypophysectomy but not 48 h after the operation. It appears, therefore, that follicles gradually lose their responsiveness to LH during the atretic process.