Expression of gonadotropin inhibitory hormone in the preoptic area and its relation with phases of estrous cycle of ewe

Introduction: Gonadotropin inhibitory hormone (GnIH) has been known as a key inhibitor of the secretion of gonadotropin releasing hormone (GnRH). Ewe has estrous cycles comprising of follicular and luteal phases. Follicular phase is in turn divided into proestrous and estrous phases. Blood level of LH increases in follicular and decreases in luteal phases. The aim of the present study was to evaluate (1) the presence of GnIH neurons in the ewe preoptic area (POA) and (2) the alterations of GnIH expression during different phases of ewe estrous cycle. Methods: Three fertile three-year-old ewes in each phase (n=9) were selected and the number of GnIH neurons was estimated by using immunohistochemistry method. Results: GnIH neurons were present in the POA during different phases of estrous cycle. The number of GnIH neurons significantly increased in the luteal phase in comparison with the proestrous phase (P=0.001). Conclusion: GnIH expression in the neurons of POA of ewe is increased in the luteal phase compared to the follicular phase. This can inhibit GnRH secretion in POA and reduce LH secretion during the luteal phase.