Abstract
Treatment of male rats with a single high dose of morphine (10 mg/kg, subcutaneously) results in a dramatic suppression of brain estradiol-2-hydroxylase activity. The suppression is blocked by naloxone and is decreased upon the development of tolerance. The injection of naloxone (0.4 mg/kg) alone produces a significant increase in brain estradiol-2-hydroxylase activity over control levels. The effects of the opiate agonists and antagonists on the activity of this brain enzyme coincide in degree and direction with their effects on plasma lutropin (luteinizing hormone) concentrations. Because the 2-hydroxyestrogens were shown to induce pituitary lutropin release, the present results indicate that the action of opiates, endogenous or exogenous, on pituitary gonadotropin release can be mediated by brain catechol estrogens.