Gonadotropin-releasing hormone binding inhibitors in the ovary

A protein present in ovaries and other tissues of many species competitively and reversibly inhibits high affinity binding of gonadotropin-releasing hormone (GnRH) to rat ovarian membranes, but this protein is not GnRH. This protein has been partially purified and characterized from bovine ovaries. The absence of GnRH binding inhibitory (GBI) activity in plasma and follicular fluid indicates that this protein may act in a localized manner within or near its site of production or release. The bovine ovarian GBI protein evokes antigonadotropic activity in ovarian cells from both the rat and the bovine. The biological effect of GBI may occur independently of interaction with high affinity binding sites for GnRH, since these are absent from the bovine ovary. Thus, the GBI protein may abrogate gonadotropin-dependent responses in ovarian cells by mechanisms separate from interaction with GnRH receptors. A complete characterization of the GBI protein and evaluation of its mechanism of action in ovarian and pituitary cells will dictate conclusions on the physiological importance of this protein.