In vitro culture of rat pre-antral follicles with emphasis on follicular interactions.

The present study was designed to determine whether rat pre-antral follicles can grow under in-vitro conditions. Emphasis is on whether follicular interaction is involved in in-vitro follicle culture, and furthermore its role in follicular development has been assessed. Pre-antral follicles were isolated mechanically from 10-day old rat ovaries. They were divided into small (50 microm < diameter < 100 microm) and large (120 microm < diameter < 200 microm) pre-antral follicles and cultured individually or in groups for 6 days in medium with or without fetal calf serum (FCS). Based on morphological criteria, large pre-antral follicles cultured in groups in serum-free medium had significantly higher survival rates than those cultured individually. In the presence of FCS, no significant difference was detected with respect to the survival. However, the large pre-antral follicles cultured in groups had a significantly greater increase in diameter than those cultured individually. Furthermore, follicles cultured in groups in FCS-containing medium exhibited significantly more follicular cell proliferation than those in serum-free medium, based on DNA measurement. The present culture system (with or without FCS) proved to be insufficient for small pre-antral follicles to stimulate growth comparable to that of large pre-antral follicles. The transmission electron microscopical (TEM) study revealed the ultrastructural differences between follicles cultured in FCS-containing and serum-free media. Taken together, the results suggest that interfollicular factors are involved in follicle development in vitro, which especially at the early folliculogenesis stage plays a positive role in terms of follicular growth as well as survival. The present culture model allows further investigation of factors that regulate early folliculogenesis.