GNRH1 and Increased circulating prolactin concentration: While prolactin could exert effects in either the pituitary or gonad, pulsatile GnRH replacement can reverse the infertility induced by hyperprolactinaemia (Polson et al. 1986, Matsuzaki et al. 1994, Lecomte et al. 1997), suggesting a prolactin-induced suppression of GnRH release is the proximal cause of infertility.