Enhanced vasoactive intestinal peptide-induced prolactin secretion from anterior pituitary cells of incubating turkeys (Meleagris gallopavo).

During incubation, female turkeys exhibit elevated circulating prolactin (PRL) which may be the result of enhanced pituitary responsiveness to vasoactive intestinal peptide (VIP). This hypothesis was tested by comparison of spontaneous and porcine VIP-induced PRL secretion from anterior pituitary cells of hens in various reproductive conditions. The effect of VIP and luteinizing hormone releasing hormone (LHRH), alone and in combination, on luteinizing hormone (LH) secretion was also examined. Incubation with pVIP (10(-10) to 10(-6) M) significantly stimulated PRL secretion at all incubation times tested (1-5 hr). This increase was greatest in cells from incubating hens, with those from laying, photorefractory, and quiescent (nonphotostimulated) hens secreting successively less PRL. These responses were obtained when spontaneous PRL secretions were compared. VIP induced approximately a similar 1.5-fold increase in LH secretion, in all reproductive groups. Also, VIP enhanced LHRH-induced LH secretion (1.2- to 1.6-fold; P less than 0.0001). It is concluded that PRL secretion in vitro by pituitary cells from turkey hens in various reproductive stages reflects the circulating levels of PRL at these stages.