Reevaluation of the role of alpha2-adrenoreceptors in morphine-stimulated release of growth hormone

D. T. Kime, L. Bartha, L. G. Harsing, G. B. Makara

Research output: Contribution to journalArticle

10 Citations (Scopus)

Abstract

The relationship between opioidergic and alpha2-adrenergic system in the regulation of GH secretion was studied using a novel alpha2-antagonist, CH-38083, and chronic treatment with yohimbine or clonidine. In male Wistar rats morphine (3 mg/kg s.c.), and clonidine (31 μg/kg i.p.) induced a significant increase in plasma GH levels. The pretreatment with the alpha2-antagonist yohimbine (1 and 3 mg/kg) effectively inhibited the GH releasing effect or morphine and clonidine. CH-38083 at the dose of 1 mg/kg did not interfere with the morphine-induced GH secretion, while it fully antagonized the GH-releasing effect of clonidine. Higher doses (3 and 5 mg/kg) of CH-38083 only partly inhibited GH secretion induced by morphine. In rats chronically treated with clonidine (2 μg/ml in the drinking water for 14 days) the GH response to an injection of clonidine was blocked, while the effect of morphine on the GH secretion remained unchanged. In long-term castrated rats the effect of clonidine (15, 31 and 250 μg/kg i.p.) on the GH secretion was significantly blunted, while the GH-releasing effect of morphine (1, 3 and 5 mg/kg s.c.) remained unchanged. The replacement of testosterone (10 mg/kg for 4 days) in castrates restored the effect of clonidine, whereas it decreased the stimulatory action of morphine on the GH secretion. In rats chronically treated with yohimbine (2 mg/kg i.p. 2-3 times daily for 14 days until sacrifice), the GH response to a high dose of clonidine (0.5 mg/kg i.p.) was blocked, while the effect of morphine (5 mg/kg s.c.) was significantly enhanced. In addition, the GH inhibitory effect of the kappa-agonist U50-488H was also lost. These findings suggest that the GH-releasing effect of morphine is a function of the opiate receptor system not mediated by the alpha2-adrenergic receptor system.

Original languageEnglish
Pages (from-to)516-522
Number of pages7
JournalNeuroendocrinology
Volume53
Issue number5
DOIs
Publication statusPublished - 1991

Keywords

  • GH secretion
  • clonidine
  • morphine
  • α-adrenoreceptor
  • κ-opiate receptor

ASJC Scopus subject areas

  • Endocrinology, Diabetes and Metabolism
  • Endocrinology
  • Endocrine and Autonomic Systems
  • Cellular and Molecular Neuroscience

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