Fraction of proliferating cells in granulosa during terminal follicular development in high and low prolific sheep breeds

During terminal development of antral follicles, granulosa cells progressively lose their proliferative activity. Romanov (ovulation rate = 3) and Ile-de-France (ovulation rate = 1) breeds of sheep were compared for fractions of proliferating granulosa cells, determined by in vitro continuous 3H] thymidine labelling. In both breeds, the fraction of proliferating cells decreased with increasing follicular size according to a sigmoid-shaped curve. After linearization, the slope of the regression line was higher (in absolute value) in Romanov, compared to Ile-de-France ewes (p = 0.02). In vivo FSH treatment led to a decrease in the slope of the regression line in Romanov ewes only (p = 0.03). These results suggest that during terminal follicular development (1) the rate of cell cycle exit is higher in granulosa cells of Romanov, compared to lie-de-France follicles, and (2) Romanov granulosa cells are more responsive to exogenous FSH in term of proliferation. These mechanisms may underlie differential dynamics of follicular development in poly- and mono-ovulating breeds of sheep.