Histologic and autoradiographic study of the in vitro effects of FGF-2 and FSH on isolated bovine preantral follicles: preliminary investigation.

Bovine early preantral follicles (40 to 65 microm diameter) were cultured for 24 or 48 h in the presence of 0, 10, 50 or 100 ng/ml of basic fibroblast growth factor (FGF-2), porcine FSH (pFSH) or both (ratio 1:1); the follicles were also exposed throughout the entire culture period to 2 microCi/ml ((3)H) thymidine. The effects of these factors on oocyte morphology and follicular DNA synthesis were then analyzed. Autoradiography was performed on histological serial sections of follicles after the culture period. Oocyte morphology of each follicle and the rate of follicular DNA synthesis were evaluated at the same time. Oocyte morphology was considerably altered in the presence of exogenous FSH. This effect seemed to be reduced by FGF-2, at least up to 24 h of culture. Analyzable incorporation of ((3)H) thymidine was only detected after 48 h of culture. The FGF-2 significantly increased the number of labeled nuclei per follicle whereas pFSH did not. This responsiveness of granulosa cells to FGF-2 disappeared in the presence of pFSH. No correlation was found between the number of labeled nuclei per follicle and the morphology of its oocyte. These results suggest that in cultured bovine early preantral follicles, pFSH induces oocyte degeneration and that this degeneration seems to be attenuated by FGF-2. In addition, FGF-2 lead to an increase in follicular DNA synthesis that disappeared in the presence of pFSH.