ROLE OF VASOACTIVE-INTESTINAL-PEPTIDE IN THE CONTROL OF PROLACTIN-INDUCED TURKEY INCUBATION BEHAVIOR .1. ACUTE INFUSION OF VASOACTIVE-INTESTINAL-PEPTIDE

Vasoactive intestinal peptide (VIP) stimulates prolactin (PRL) secreti on. Ovine PRL induces incubation behavior in avian species. This study was designed to determine whether VIP can elevate plasma PRL for up t o 3 h. Saline or porcine VIP (pVIP; 30, 60, or 150 ng/min) was infused into the median eminence of laying turkeys for 1 h. The 60- and 150 n g doses of pVIP increased plasma PRL (p < 0.01), whereas the 30-ng dos e was insignificant. Pituitary PRL content decreased in pVIP-treated t urkeys. Two-hour infusion of 60 or 150 ng chicken MP (cVIP)/min produc ed similar elevations of plasma PRL (p < 0.001), which declined within 80 min. Both treatments induced insignificant increases in pituitary PRL mRNA. Saline or cVIP (30, GO, or GO [pulsed] ng/min) was infused i nto the median eminence for 3 h. Sixty ng cVIP/min induced the largest PRL release (p < 0.05). The pulsatile and low-cVIP treatments resulte d in release of a significant amount of PRL in comparison to the salin e treatment (p < 0.01). Ah cVIP treatments resulted in decreased pitui tary PRL content (p < 0.05). The 60-ng dose increased PRL mRNA (p < 0. 1). This study shows that 60 ng VIP/min causes the maximum PRL release in laying turkeys. However, pituitary PRL content is depleted and PRL synthesis cannot maintain PRL secretion at high levels.