The growth hormone secretory response to fentanyl in rat: an involvement of μ type receptors

Fentanyl, a selective μ opioid receptor agonist, administered intravenously, influences growth hormone secretion in conscious male rats. A dose-response study demonstrated that the maximum growth hormone release was obtained with 10 μg/kg while higher doses were less or not effective. MR-2266 (6 mg/kg iv), a μ and κ opioid receptor antagonist, and bremazocine (0.1 mg/kg iv) a μ opioid receptor antagonist with κ agonistic properties, both potently inhibited the growth hormone response to fentanyl (10 μg/κg iv). In contrast, the effect of fentanyl on growth hormone release was not blocked in rats treated with either ICI-154129 (30 mg/kg iv or 150 μg/kg intracerebroventricularly a selective δ opioid receptor antagonist, or U-50488 (10 mg/kg iv), a specific κ opioid receptor agonist. These results suggest that opioid receptors of the μ type are involved in the fentanyl-induced growth hormone release. © 1990, Italian Society of Endocrinology (SIE). All rights reserved.SCOPUS: ar.j