Insulin-like growth factor binding protein-3 inhibits gonadotropin-induced ovulation, oocyte maturation, and steroidogenesis in rabbit ovary.

The effects of insulin-like growth factor binding proteins (IGFBPs) on human CG (hCG)-induced oocyte maturation, ovulation, steroidogenesis, and intrafollicular plasminogen activator (PA) activity were investigated in rabbit ovaries perfused in vitro. The addition of IGFBP-3, but not IGFBP-1, to the perfusate dose dependently inhibited hCG-induced ovulation, whereas ovulation failed to occur in any ovaries perfused with medium or IGFBP-3 alone. IGFBP-3 (100 ng/ml) significantly inhibited the resumption of meiosis in ovulated ova and follicular oocytes in hCG-treated ovaries, as well as the hCG-stimulated production of estradiol (E2), but not progesterone, by the perfused ovaries. Intrafollicular PA activity increased significantly within 1 h after exposure to hCG, reaching a maximum at 4 h; IGFBP-3 significantly inhibited hCG-stimulated intrafollicular PA activity. The blockade of hCG-induced ovulation by IGFBP-3 correlated with the reduction in intrafollicular PA activity. Treatment with hCG induced a 2....