Involvement of Peptide Histidine Isoleucine (PHI) In Prolactin Secretion Induced by Serotonin in Rats

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Abstract
The possible role of hypothalamic peptide histidine isoleucine (PHI) in prolactin (PRL) secretion induced by serotoninergic mechanisms was investigated in male rats using a passive immunization technique. Intracerebroventricular injection of serotonin (5HT, 10 .mu.g/rat) raised plasma PRL levels both in urethane-anesthetized rats and in conscious rats pretreated with normal rabbit serum (0.5 ml/rat, iv, 30 min before). Plasma PRL responses to 5HT were blunted in these animals when they were pretreated with rabbit antiserum specific for PHI (0.5 ml/rat, iv. 30 min before) (mean .+-. SE peak plasma PRL: anesthetized rats 271.3 .+-. 38.3 ng/ml vs 150.0 .+-. 12.6 ng/ml, P < 0.01, conscious rats 54.3 .+-. 6.8 ng/ml vs 30.7 .+-. 4/1 ng/ml, p < 0.025). These results suggest that hypothalamic PHI is involved, at least in part, in PRL secretion induced by central serotoninergic stimulation in the rat.