INSULIN-LIKE GROWTH-FACTOR-I RECEPTORS IN OVARIAN GRANULOSA-CELLS - EFFECT OF FOLLICLE SIZE AND HORMONES

The objectives of the present studies were to determine if the numbers of IGF-I receptors in bovine granulosa cells differed with size of fo llicle and to determine if growth factors and hormones affected the nu mber of IGF-I receptors in granulosa cells. Granulosa cells from small (1-5 mm) and large (greater than or equal to 8 mm) follicles were cul tured for 2-4 days in 10% FCS and then assessed for levels of IGF-I re ceptors. Numbers of IGF-I receptors were 15-fold greater in granulosa cells from large than small follicles. In addition, bFGF (5 and 50 ng/ ml) decreased whereas estradiol (1 mu g/ml), FSH (10 ng/ml) and EGF (1 0 and 100 ng/ml) increased the number of IGF-I receptors in granulosa cells from small follicles. These hormones had no effect on the number of IGF-I receptors in granulosa cells from large follicles. In conclu sion, granulosa cells from large follicles have a greater number of IG F-I receptors than cells from small follicles, and thus, it appears th at granulosa cells acquire a greater number of IGF-I receptors during the process of differentiation.