In-vivo bioactivity of gonadotrophin surge attenuating factor (GnSAF)

Gonadotrophin surge attenuating factor (GnSAF) is a nonsteroidal ovarian factor responsible for the attenuation of the endogenous LH surge in superovulated cycles. To study the bioactivity of GnSAF in vivo, the pituitary response to exogenous GnRH was investigated in 13 normally ovulating women during spontaneous and FSH-treated cycles. GnRH experiments were performed at three stages of both spontaneous and FSH cycles, i.e. early (n = 8), mid- (n = 8) and late follicular phase (n = 8). LH response to GnRH increased significantly from the early to late follicular phase in the spontaneous cycles, while in the FSH cycles it decreased significantly in mid- and increased in late follicular phase. A marked attenuation of the LH response to GnRH during both the mid- and late follicular phase was seen in the FSH as compared to the corresponding spontaneous cycles. We conclude that in superovulated cycles small, growing follicles produce GnSAF.