Stimulation of prolactin release in turkeys by vasoactive intestinal peptide.

Vasoactive intestinal peptide (VIP) is a potent releasor of prolactin in birds. The main purpose of this study was to identify its site of action. Synthetic porcine VIP administered intraatrially to freely moving ovariectomized (OVX) turkeys induced an elevation of circulating PRL within 15 min in a dose-related manner. Removal of hypothalamic control of PRL release by surgical disconnection of the neurohemal regions of the median eminence did not significantly diminish the PRL response to VIP. Intraatrial injection of eledoisin or bradykinin into OVX hens did not influence PRL secretion, indicating that the PRL releasing activity of VIP is probably not attributable to its vasodilatory action. These results support the possibility that VIP is an authentic prolactin releasing factor (PRF) in birds.