Review

Gonadotropin surge attenuating factor: Α physiological regulator

Messinis Ioannis, Messini Christina, Dimitraki Marina, Anifandis George, Dafopoulos Konstantinos

Department of Obstetrics and Gynecology, University of Thessaly, School of Health Sciences, Faculty of Medicine, Larissa, Greece

Correspondence: Messinis Ioannis, Department of Obstetrics and Gynecology, University of Thessaly, School of Health Sciences, Faculty of Medicine, GR – 41110 Larissa, Greece, E – mail: messinis@med.uth.gr


Abstract

Gonadotropin surge attenuating factor (GnSAF) is a non- steroidal ovarian substance, which attenuates the endogenous LH surge in superovulated women. Although several attempts have been made to purify GnSAF from various biological materials, different sequences were found. Only one of them has shown substantial homology of GnSAF to a known portion of the human genome. In particular, GnSAF showed identity to the carboxyl – terminal fragment of human serum albumin (HSA) with a molecular mass of 12.5 kDa. Additional in vitro experiments have confirmed the above finding, since recombinant polypeptides corresponding to the subdomain IIIB of HSA displayed GnSAF bioactivity in an in vitro bioassay system, while the expression of HSA gene was detected in human granulosa cells. Accumulated evidence has indicated that GnSAF may play an important physiological role during the normal menstrual cycle. Thereby, it is assumed, that the bioactivity of GnSAF increases during the intercycle period under the stimulating action of FSH and decreases gradually, thereafter, until the midcycle. This factor seems to be the missing substance in the ovarian feedback system, which maintains the pituitary in a state of low responsiveness to GnRH during the greater part of the follicular phase. The reduced bioactivity
of GnSAF in the late follicular phase enhances the sensitizing effect of estradiol on the pituitary response to GnRH, facilitating thus the full expression of the midcycle LH surge.

Keywords: LH, GnRH, GnSAF, ovary, pituitary

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