Evidence that neuropeptide Y (NPY) released into the hypophysial-portal circulation participates in priming gonadotropes to the effects of gonadotropin releasing hormone (GnRH).

NPY exhibits modulatory activity at both the adenohypophysial and the central levels of the rat hypothalamic-pituitary-gonadal axis. In the present studies, the secretion and physiological activity of endogenous irNPY was examined. We have shown that: (i) irNPY is secreted into the hypophysial-portal circulation, (ii) hypophysial-portal concentration profiles of irNPY and irGnRH are parallel throughout the rat estrous cycle, and (iii) removal of endogenous NPY via immunoneutralization inhibits the steroid-induced LH surge in ovariectomized rats. From these observations, we speculate that NPY secreted into the hypophysial-portal circulation participates in priming of gonadotropes to the actions of GnRH on the afternoon of the preovulatory surge.