Abstract
The 5α-reduced androgens have been implicated as antagonists of follicular development. In this experiment, we examined the effect of active immunization against 5α-reduced androgen on follicular development in ewes. During the breeding season, cyclic Merino ewes were either actively immunized three times against 5α-androstane-3α,17β-diol (3α-diol) or served as controls. Six to nine weeks after the last immunization, they were treated with PGF 2α analog (PG, 125 mg cloprostenol i.m.) and luteolysis was induced. Fourteen days after the PG treatment, the ewes were either killed (mid-luteal phase) or treated a second time with PG and killed 24 h later (early follicular phase). At slaughter, blood samples were collected and ovaries recovered. All CL and follicles larger than 2 mm were dissected and their size and appearance were recorded. Follicular fluid was collected and concentrations of estradiol-17β (E 2), progesterone (P), androstenedione (A 4), testosterone (T), dihydrotestosterone (DHT), 5α-androstane-3α-ol,17β-one (androsterone: 3α-ol) and 3α-diol were determined by RIA. Immunization induced antibodies primarily to DHT and its 5α-reduced substrates 3α-diol and 3α-ol but not to E 2, P, A 4 or T. Immunization increased ovulation rate, size of ovulatory follicles and weight of CL. Immunization appeared to increase ovulation rate by decreasing the incidence of atresia in large preovulatory follicles. Regardless of their physiological status follicles contained only low levels of DHT; 3α-ol and 3α-diol were not detected in most follicles. Immunization did not appear to affect levels of DHT or other steroids in the follicular fluid. In conclusion, the induction of antibodies to 5α-reduced androgens increases ovulation rate by enhancing follicular viability during the preovulatory period in ewes. However, this effect is not brought about by the direct immune-neutralization of DHT or its 5α-reduced substrates 3α-ol and 3α-diol at the ovarian level.
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