Impact of exogenous progesterone on ovarian follicular dynamics and function in mice

Raising progesterone concentrations in young adult mice by subcutaneous implants resulted in ovulation being blocked and the cessation of oestrous cycles. The effect of this treatment on the numbers and dynamics of preantral follicles during 36 days of treatment was studied using a compartmental model to analyse differential follicle counts. Changes in growth and/or death rates were detected at all stages of follicular development. An increased rate of growth through preantral stages was predicted in the treatment group when compared with the controls, but most of these follicles did not reach the antral stage of development as an increased death rate was observed at large preantral stages (stage IV). Antral follicles were formed in the treatment group, but all succumbed to atresia. Increased atresia in the antral population of follicles in the treatment group was observed directly.