Figure 1.

The role of gonadotropin-inhibitory hormone (GnIH) under physiological and stress conditions. (A) GnIH participates in the control of physiological GnRH/luteinizing hormone (LH) regulation. GnIH activity is decreased by high estrogen concentrations at the time of the GnRH/LH surge. This alteration promotes both ovulation and reproductive behaviors and consequently increases the chance of pregnancy. (B) On the other hand, GnIH plays roles in stress-induced reproductive dysfunction. GnIH expression and activity are increased by stress, and this alteration suppresses the hypothalamic–pituitary–gonadal axis action by inhibition of GnRH/LH secretion. It also decreases reproductive behavior and, consequently, decreases the chances of pregnancy and induces infertility. Such stress-induced changes of GnIH may be partially induced by corticosterone secreted from the adrenal gland.