A Model for the Study of Androgen Effects on Follicular Atresia and Ovulation1

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Abstract
Hypophysectomized (day 24), immature female rats were given pregnant mare''s serum gonadotropin (PMSG, 32 IU) to initiate follicular growth and human chorionic gonadotropin (hCG, 10 IU) to induce ovulation comparable to that observed in an adult, cycling rat. The effects of a nonaromatizable androgen, 5.alpha.-dihydrotestosterone (DHT), on the ovarian follicular population and ovulation were assessed. A single injection of DHT (2 or 4 mg/kg body wt) 30 h after PMSG resulted in decreased ovarian weight compared to PMSG controls. This ovarian weight reduction was associated with a stimulation of follicular atresia and reduction in the number of healthy primary, secondary and tertiary follicles. A 24 h exposure of the PMSG-primed hypophysectomized rat to 1 or 4 mg/kg body wt DHT resulted in 53.7 .+-. 3.8 and 66.7 .+-. 7.8 atretic follicles, respectively; values significantly higher (P < 0.05) than the 32.2 .+-. 2.7 atretic follicles observed in PMSG controls. This DHT-induced atresia was correlated with decreases in healthy follicles of all types as well. These changes in ovarian histology with DHT administration were reflected in a loss of in vivo responsiveness of the ovary to hCG. DHT treatment reduced the number of ova present in the oviducts from 14.9 .+-. 1.2 with PMSG alone to 7.8 .+-. 1.2. Co-administration of estradiol (1 or 2 mg/kg body wt) prevented the atretic effects of DHT as measured by histological appearance of the follicles and restoration of ovulation to PMSG levels. This model permits examination of ovarian changes due to steroid treatment on biological function and verification of histological assessment of the ovary by testing the in vivo responsiveness of follicles to hCG. DHT induces atresia of ovarian follicles and the androgen effect can be prevented by simultaneous treatment with estradiol, suggesting that androgen-induced atresia may involve interference in the production and/or action of estradiol in the ovary.