EFFECTS OF GONADOTROPIN DEPRIVATION ON FOLLICULAR-GROWTH IN GILTS

The endocrine and ovarian effects of hypophysectomy (n = 5) and gonado trophin-releasing hormone (GnRH) antagonist administration (Antarelix) (n = 5) were studied in gilts by comparison with control animals (n = 6). All gilts were given Regumate (20 mg/d for 18 d). The last day of Regumate was day 0. Hypophysectomy and initiation of Antarelix admini stration (0.6 mg iv twice daily for 7 d) were performed on day 5. All ovaries were obtained at slaughter on day 12. Blood samples were obtai ned daily from all Antarelix-treated and control sows to measure lutei nizing hormone (LH) and follicle stimulating hormone (FSH) concentrati ons. Frequent sampling was performed on day 10 on control and Antareli x-treated gilts to assess pulsatile LH secretion. Oestrus or LH surge was initiated before the beginning of treatment in 2 hypophysectomized , 4 Antarelix-treated, and 4 control females. Gonadotropins were undet ectable in the blood of hypophysectomized sows on day 6. On day 10, pu lsatile LH release was blocked in Antarelix-treated gilts. At no time were FSH concentrations significantly affected. Histological observati on of the ovaries demonstrated that: (i) similar populations of health y or total (healthy + atretic) follicles < 1 mm were found in the 3 gr oups of females; (ii) healthy follicles 1 to 2 mm in diameter were pre sent in Antarelix-treated but not in hypophysectomized gilts; and (iii ) healthy follicles > 2 mm were absent in Antarelix-treated and hypoph ysectomized gilts. The present study suggests the existence of 3 subgr oups amongst antral follicles (gonadotropin independent: 0.19 to 1.1 m m; FSH dependent: 1.1 to 2 mm; LH pulses dependent: > 2 mm in diameter ).