The Nature and Function of Putative Gonadotropin Surge-Attenuating/Inhibiting Factor (GnSAF/IF)

REGULATION of the ovarian cycle is by a complex series of positive and negative feedback mechanisms between ovary, hypothalamus, and pituitary. The role of steroidal feedback between ovary, pituitary, and hypothalamus has been known for many years, and our knowledge of the mechanisms involved continues to expand. Nonsteroidal ovarian secretagogues also have endocrine regulatory function, some acting centrally. The best known of these is inhibin, although its central function is now uncertain. Since the late 1970s it has become evident that there are ovarian nonsteroidal products with specific inhibitory effects on pituitary responsiveness to GnRH. As early as 1979 (1) it was suggested that follicular fluid contained a factor other than inhibin that suppressed GnRH-induced LH secretion in vitro. Recent reviews of a novel ovarian factor, which has been called gonadotropin surge-attenuating factor (GnSAF) or gonadotropin surge-inhibiting factor (GnSIF), have supported the evidence for its existence and possible physiological role (2–6). Reviews of the LH surge itself have begun to include reference to this ovarian product (7). In this review we concentrate on the nature, activity, and probable role of GnSAF/IF in the regulation of LH secretion during the ovarian cycle.