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. 0 1988 Society for Experimental Biology and Medicine.
Prolactin (PRL) secretion by monolayer cultures of turkey anterior pituitary cells was significantly increased (up to 44-fold) by vasoactive intestinal peptide (VIP), arginine vasotocin (AVT), and by an extract of turkey hypothalami (HE). Several other neuropeptides (including thyrotropin-releasing hormone) and neurotransmitters were ineffective in influencing PRL secretion at doses up to M. The dynamic PRL response to HE and VIP was studied using superfused pituitary cells attached to microcamer beads. HE, administered in 30-min pulses, resulted in a significant, dose-related increase in PRL secretion from a basal secretion rate of 2.32 ng/min/ 10' cells to a peak secretion rate of 127.13 ng/min/lO' cells at the highest dose of HE tested (1 mg tissue-equivalent weight/ml). VIP significantly increased PRL secretion at all doses studied (from lo-'' to M), with lo-* M VIP producing a response similar to that observed with 1 mg/ml HE. A highly significant (P < 0.001) linear relationship was demonstrated between the logdose of VIP administered and peak PRL secretion rate. These studies suggest that VIP, but not TRH, may be a physiological stimulus for PRL release in the turkey. 0
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