Vasoactive Intestinal Peptide Stimulates Chick Pineal Melatonin Production and Interacts with Other Stimulatory and Inhibitory Agents but Does Not Show α1-Adrenergic Potentiation

Vasoactive intestinal peptide (VIP) is known to mimic the effects of beta-adrenergic receptor stimulation in the rat pineal, including marked potentiation by alpha 1-adrenergic receptor stimulation, and to cause increased melatonin synthesis. In contrast, the chick pineal does not respond to beta-adrenergic stimulation, and melatonin synthesis is inhibited by norepinephrine via an alpha 2-adrenergic receptor. The present experiments show that chick pineal cells in primary culture do, however, respond to VIP with increased melatonin production. The effect of VIP was inhibited by addition of norepinephrine or of nitrendipine or by exposing the cells to "unexpected" white light. Stimulation by VIP was enhanced by addition of forskolin or Bay K 8644 but not by alpha 1-adrenergic receptor stimulations. Although stimulation by VIP appears similar in the chick pineal to that seen in the rat pineal and other systems, "dual-receptor regulation," at least with alpha 1-adrenergic receptors, appears to be absent.