Decrease of morphine-induced prolactin release by a procedure causing prolonged stress

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Abstract
The effects of morphine and fentanyl on plasma prolactin levels in rats have been measured. It was found that a prolonged immobilization stressful procedure for 5 h inhibited the response to morphine and fentanyl to increase prolactin secretion, but did not influence the increase in plasma prolactin caused by haloperidol. The injection of a large dose of cortisol (25 mg/kg, s.c.) also evoked an inhibition of morphine-induced prolactin release. The inhibition was maximal 24 h after the administration of the glucocorticoid. These results indicate that stress may induce prolonged alteration in endogenous opioid-mediated neuro-modulation via a prolonged release of glucocorticoids. J. Endocr. (1984) 101, 169–172