Opioid-receptor blockade blunts growth hormone (GH) secretion induced by GH-releasing hormone in the human male

Objective: To investigate the existence of an opioid stimulatory tone on growth hormone (GH) secretion in the human male. Design: Seven healthy male volunteers, aged 19-30, were studied in the Endocrine Unit of the University of Sassari. GH-releasing hormone (GHRH), 100 mu g as an intravenous (IV) bolus, as administered with and without preadministration of IV naloxone, 2 mg as a bolus followed by a constant infusion of 2 mg/h. Blood samples were taken for 120 minutes after GHRH administration. Results: Naloxone significantly blunted the GH response to GHRH, measured either as mean peak value (at times 30 to 90) or as integrated concentrations. Conclusions: Naloxone is able to decrease the effect of a maximal dose of GHRH, thus suggesting the existence of an opioid stimulatory tone on GH secretion. Z9 3