SEROTONERGIC STIMULATION OF PROLACTIN SECRETION IS INHIBITED BY VASOACTIVE-INTESTINAL-PEPTIDE IMMUNONEUTRALIZATION IN THE TURKEY

The neuronal mechanisms that govern prolactin (PRL) secretion in the t urkey appear to involve monoaminergic systems. Considerable evidence i ndicates that serotonin (5-HT), acting centrally, is a potent stimulat or of PRL secretion. This study, using birds actively immunized agains t VIP, tests the hypothesis that 5-HT stimulates PRL secretion by rele asing vasoactive intestinal peptide (VIP). Nonimmunized turkeys were i njected ip with saline, quipazine (5-HT agonist; 5 mg/kg), methysergid e (5-HT antagonist; 8 mg/kg), or methysergide plus quipazine, and VIP- immunized birds were injected with saline or quipazine. Quipazine incr eased plasma PRL revels from 26.8 +/- 7.1 ng/ml at Time 0 to a peak va lue of 148.1 +/- 31.4 ng/ml 2 hr after injection. Pretreatment with me thysergide or VIP-immunoneutralization abolished the PRL response to q uipazine. Intraventricular infusion of 5-HT (1 nmol/min) caused plasma PRL to rise from a baseline of 16.3 +/- 2.6 ng/ml to 85.2 +/- 14.3 ng /ml after 30 min in nonimmunized control birds. Serotonin infusion did not induce PRL secretion in the VIP-immunized birds. These findings s uggest that serotonergic stimulation of PRL secretion in the female tu rkey requires a functional VIPergic system. (C) 1995 Academic Press, I nc.