Effect of naloxone or levallorphan on serum prolactin concentrations and apomorphine-induced growth hormone secretion.

Naloxone HCl (0.8 mg intravenously; n=9) or levallorphan tartrate (0.25 mg subcutaneously; n=5) had no effect on basal prolactin or growth hormone secretion in normal men. Neither narcotic antagonist inhibited the growth hormone secretory response to apomorphine HCl (0.75 mg subcutaneously). These findings suggest that narcotic antagonists do not block dopamine receptors in the hypothalamic-pituitary axis in man and that if these agents have antischizophrenic properties then these are not mediated by dopamine receptor blockade.