Ovarian regulation of gonadotropin secretion

Dafopoulos KC, Kallitsaris A, Messinis IE

Department of Obstetrics and Gynecology, University of Thessaly, Larissa, Greece

Correspondence: Dafopoulos KC, Department of Obstetrics and Gynecology, University of Thessaly, University hospital of Larissa, GR-41110, Larissa, Greece

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Abstract

Hypothalamus is the main regulator of reproductive function, responding to both peripheral and central nervous system messages and exerting its influence by means of neurotransmitters transported to the pituitary. Steroidal and non-steroidal ovarian hormones also play a substantial role in the normal reproductive function. During the follicular phase of the normal menstrual cycle, estradiol (E2) mediates the ovarian mechanism that controls basal gonadotrophin secretion, while at midcycle a positive effect is expressed and the endogenous LH surge occurs. During the normal menstrual cycle, E2 sensitizes the pituitary to GnRH, an action that in the early to midfollicular phase is counteracted by GnSAF. In the late follicular phase, the sensitizing effect of E2 is facilitated both by a decrease in the production of GnSAF and by the synergistic action of E2 and progesterone. With these hormonal interactions, the secretion of LH up to the midfollicular phase is maintained at a low level and is only markedly enhanced at midcycle when high amounts of this hormone are required for the ovulatory events. Inhibins and activins may play a role in regulating the "FSH window" and therefore the recruitment and selection of the dominant follicle.

Key words: gonadotropins; ovarian steroids; GnSAF; inhibins; activins