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Serotonergic stimulation of prolactin secretion is inhibited by vasoactive intestinal peptide immunoneutralization in
M E el Halawani1, O M Youngren, I Rozenboim
1Department of Animal Science, University of Minnesota, St. Paul 55108, USA.
Abstract:
The neuronal mechanisms that govern prolactin (PRL) secretion in the turkey appear to involve monoaminergic systems. Considerable evidence indicates that serotonin (5-HT), acting centrally, is a potent stimulator of PRL secretion. This study, using birds actively immunized against VIP, tests the hypothesis that 5-HT stimulates PRL secretion by releasing vasoactive intestinal peptide (VIP). Nonimmunized turkeys were injected ip with saline, quipazine (5-HT agonist; 5 mg/kg), methysergide (5-HT antagonist; 8 mg/kg), or methysergide plus quipazine, and VIP-immunized birds were injected with saline or quipazine. Quipazine increased plasma PRL levels from 26.8 +/- 7.1 ng/ml at Time 0 to a peak value of 148.1 +/- 31.4 ng/ml 2 hr after infection. Pretreatment with methysergide or VIP-immunoneutralization abolished the PRL response to quipazine. 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 suggest that serotonergic stimulation of PRL secretion in the female turkey requires a functional VIPergic system.