The participation of hypothalamic dopamine in morphine-induced prolactin release in man.

In order to assess the role of dopamine in opiate-induced prolactin secretion, morphine alone or in combination with the dopamine blocker metoclopramide, or the L-aromatic aminoacid decarboxylase inhibitor benserazide, was administered to a group of normal adult men. Morphine (10 mg) stimulated prolactin release in all subjects; however, the effect was totally abolished when 10 mag metoclopramide or 200 mg benserazide were given before the opiate agonist. The prolactin releasing effect of a sub-maximal metoclopramide dose (1 mg) was potentiated by morphine. In vitro, benserazide was totally inactive in stimulating prolactin release by isolated anterior pituitary cells. Moreover, benserazide failed to alter the inhibiting action of dopamine on prolactin release. The data suggest that opiates stimulate prolactin release in man by acting through dopaminergic mechanisms.