The role of kisspeptin and gonadotropin inhibitory hormone (GnIH) in the seasonality of reproduction in sheep.

Sheep are seasonal breeders and reproductive status is controlled by photoperiod. Recent recognition of the significant role for kisspeptin and gonadotropin inhibitory hormone (GnIH) in the regulation of gonadotropin releasing hormone (GnRH) cells has provided a new perspective in the seasonal regulation of reproductive activity. Virtually all kisspeptin cells express estrogen receptors and kisspeptin is a potent stimulator of GnRH secretion. Thus, kisspeptin cells provide a conduit by which changes in estrogen feedback effects may be exerted upon GnRH cells. Changes in the activity of kisspeptin cells with season indicate a major role in the seasonal changes in reproductive activity in the ewe. GnIH is an inhibitor of reproductive function and there is mounting evidence that changing activity of this system is also an important determinant of reproductive status. Reciprocal changes in kisspeptin and GnIH activity explain seasonal changes in the function of GnRH cells.