EFFECT OF GONADOTROPIN TREATMENT ON SIZE, NUMBER, AND CELL-PROLIFERATION OF ANTRAL FOLLICLES IN COWS

To determine the effects of gonadotropins on the size, number, and cel l proliferation of antral ovarian follicles, cows received FSH-P or ve hicle beginning on Day 2 after estrus, and ovaries were collected 6, 1 2, 24, or 48 hr after the initiation of FSH-P treatment or 24 or 48 hr after the initiation of vehicle treatment. Ovaries also were collecte d from untreated cows on Day 2 after estrus (pretreatment). Before fix ation, all visible antral follicles were counted and their surface dia meters were recorded. Proliferating cells were immunolocalized in fixe d follicles by using a specific primary antibody against proliferating cell nuclear antigen (PCNA), and the labeling index (LI; percentage o f cells staining positively for PCNA) was determined for granulosa and thecal cells. After 48 hr of treatment, FSH-P-treated cows had fewer (P < 0.01) small antral follicles and more medium and large antral fol licles (P < 0.01 and P < 0.05, respectively) compared with vehicle-tre ated cows. Granulosa cell LI was negatively correlated (P < 0.05) with follicular diameter for vehicle-treated but not for FSH-P-treated cow s. Analysis of covariance using follicular diameter as a covariate to adjust to a common diameter indicated that granulosa cell LI was great er (P < 0.05) at 24 and 48 hr in FSH-P-treated than in vehicle-treated cows; conversely, thecal cell LI was greater (P < 0.01) at 48 hr in F SH-P-treated compared with vehicle-treated cows but did not differ at 24 hr. Across all groups, the LI of cells located within the antral ha lf of the granulosa cell layer was greater (P < 0.01) than that of cel ls located within the basal half. In conclusion, the stimulation of fo llicular development by exogenous gonadotropins increased or maintaine d the proliferation of granulosa and thecal cells concomitant with con tinued follicular growth. Therefore, enhanced follicular cell prolifer ation may be an important mechanism by which FSH-P superinduces the gr owth of antral follicles in cows. (C) Elsevier Science Inc. 1997.