HYPOTHALAMIC AND POSTERIOR PITUITARY CONTENT OF VASOACTIVE-INTESTINAL-PEPTIDE AND GONADOTROPIN-RELEASING HORMONES-I AND HORMONES-II IN THE TURKEY HEN

An inverse relationship often exists between prolactin (Prl) and LH in avian species. Our study was designed to investigate the relationship between hypothalamic and posterior pituitary vasoactive intestinal pe ptide (VIP)-an endogenous Prl-releasing peptide-and chicken GnRH-I and GnRH-II. Hypothalamic VIP content was increased after photostimulatio n, reaching its highest levels in incubating and photorefractory birds . The highest hypothalamic GnRH-I content was in laying hens followed by that in photostimulated and incubating birds. The lowest levels wer e in the nonphotostimulated birds. Hypothalamic GnRH-II increased afte r photostimulation, then fell to nonphotostimulated levels during incu bation and photorefractoriness. Posterior pituitary VIP content was el evated in response to photostimulation, reaching a peak value in the l aying and incubating birds, then declining in the photorefractory hens . Posterior pituitary GnRH-I and GnRH-II content peaked in the incubat ing birds. Ovariectomy caused a significant reduction in hypothalamic GnRH-I and GnRH-II with no effect on VIP; no changes were found in the posterior pituitary due to ovariectomy. Reducing day length caused a significant decrease in the hypothalamic and the posterior pituitary c ontent of VIP and GnRH-I, and GnRH-II. Ovine Prl (oPrl) administration to laving hens reduced the hypothalamic VIP and GnRH-I and GnRh-II co ntent. Posterior pituitary GnRH-I content was also reduced. Although G nRH-II levels were reduced by Day 4 of injections, they rose to peak l evels by Day 14 of oPrl administration. Posterior pituitary VIP conten t was not altered by oPrl.