Studies on rat luteal cell response to insulin-like growth factor I (IGF-I): identification of a specific cell membrane receptor for IGF-I in the luteinized rat ovary.

Insulin-like growth factor-I (IGF-I) has been shown to stimulate biosynthesis of progesterone and other differentiated functions of granulosa cells. The presence of the IGF-I receptor messenger RNA and IGF-I receptor as well as the role of IGF-I in the amplification of gonadotropin action in luteinized rat ovarian cells were assessed in the present study. Rat ovarian luteal tissue were obtained on day 6 of pseudopregnancy. After collagenase dispersion, luteal cells were cultured with or without IGF-I for 72 h in a serum-free medium in the absence or presence of human CG (100 ng/ml), 8-bromo-cAMP (1 mM), and 25-OH cholesterol (30 ng/ml). IGF-I alone increased (P < 0.01) progesterone secretion 47% over controls. When combined with hCG the increase in progesterone secretion was enhanced 6-fold (P < 0.001) over controls. The effects of 8 bromo-cAMP on progesterone secretion also was amplified (P < 0.001) when IGF-I was present in the medium. When 25-OH cholesterol, a diffusable substrate for steroidogenesis, ...