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

The present study was designed to determine whether rat pre-antral follicle s can grow under in-vitro conditions. Emphasis is on whether follicular int eraction is involved in in-vitro follicle culture, and furthermore its role in follicular development has been assessed. Pre-antral follicles were iso lated mechanically from 10-day old rat ovaries. They were divided into smal l (50 mu m < diameter < 100 mu m) and large (120 mu m < diameter < 200 mu m ) pre-antral follicles and cultured individually or in groups for 6 days in medium with or without fetal calf serum (FCS). Based on morphological crit eria, large pre-antral follicles cultured in groups in serum-free medium ba d 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 h ad a significantly greater increase in diameter than those cultured individ ually. Furthermore, follicles cultured in groups in FCS-containing medium e xhibited significantly more follicular cell proliferation than those in ser um-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 tra nsmission electron microscopical (TEM) study revealed the ultrastructural d ifferences between follicles cultured in FCS-containing and serum-free medi a. Taken together, the results suggest that interfollicular factors are inv olved in follicle development in vitro, which especially at the early folli culogenesis stage plays a positive role in terms of follicular growth as we ll as survival. The present culture model allows further investigation of f actors that regulate early folliculogenesis. (C) 2000 Wiley-Liss, Inc.