On the role of dopamine receptors in the naloxone-induced hormonal changes in man.

To assess the role of dopamine receptors in naloxone-induced hormonal changes, the effects of dopamine and metoclopramide on anterior pituitary hormone secretion were studied during the infusion of the opiate blocker in normal men. Naloxone stimulated LH and cortisol secretion in all subjects, whereas FSH, TSH, PRL, and GH did not change. The infusion of dopamine completely suppressed the naloxone-induced LH rise; on the contrary, metoclopramide failed to alter the magnitude of the increments in LH observed during the infusion of the opiate blocker. The cortisol response to naloxone remained unchanged during dopamine and metoclopramide infusion. Metoclopramide stimulated PRL and TSH release during naloxone treatment, whereas dopamine suppressed PRL and TSH secretion. The data do not suggest a participation of dopamine receptors in the naloxone-induced hormonal changes in man and confirm a suppressive effect of dopamine infusion on LH release in humans.