STIMULATION OF PROLACTIN SECRETION BY MORPHINE - ROLE OF THE CENTRAL SEROTONERGIC SYSTEM

Unanesthetized male rats with indwellinh right atrial cannulae were injected with morphine (MOR) i.v. which produced a dose-related increase in plasma prolactin levels (PRL). This effect was blocked partially by naloxone (NAL) at a dose of 0.06 mg/kg and totally by 0.6 mg/kg NAL. Interruption of central serotonergic neurotransmission by receptor blockade, with metergoline (MET) or cyproheptadine (Cypro), inhibition of tryptophan hydroxylase by para-chlorophenylalanine or destruction of serotonin neurons by 5, 7-dihydroxytryptamine antagonized the morphine (3 mg/kg) induced elevation in PRL release. Depression of dopaminergic activity with α-methyl-para-tyrosine elevated the basal PRL levels, but it did not prevent a further increase of prolactin levels by morphine (3 mg/kg). These data are compatible with the hypothesis that morphine stimulates PRL release by activation of the central serotonergic system. © 1979.