Development of primordial and prenatal follicles from undifferentiated somatic cells and oocytes in the hamster prenatal ovary in vitro: Effect of insulin

Fetal hamster ovaries were cultured for up to 16 days in the presence or ab sence of various dosages of insulin to evaluate the induction of folliculog enesis in vitro. In the absence of insulin, a few primordial follicle-like structures appeared by the 4th day, and distinct primary follicles (stage 1 ) appeared by the 12th day of culture. The organelles in the oocytes and ad jacent granulosa cells developed along with follicular growth. Moreover, ga p junctions between the oocyte and somatic cell plasma membrane also develo ped as early as 8 days in culture. In the presence of 0.2 mu g/ml insulin, primary follicles developed after 8 days, and similar to 4% secondary follicles with 2-3 layers of granulosa c ells appeared after 16 days of culture. However, higher dosages (> 0.2 mu g /ml) of insulin retarded primary follicle formation and induced the formati on of primordial follicles with larger oocytes. An increased number of larg er oocytes with a few granulosa cells accumulated at the periphery of the o vary. The results indicate that although primordial and primary follicles c an develop after 12 days in vitro in the absence of exogenous insulin, the latter is required for timely progression of follicular development through primary and secondary stages.