Hypothalamic α2A-adrenoceptors stimulate growth hormone release in the rat

G. Makara, Do T. Kiem, E. Vízi

Research output: Contribution to journalArticle

8 Citations (Scopus)

Abstract

Oxymetazoline, the relatively selective α2A-adrenoceptor agonist (with more than 60-fold selectivity over the α2B-adrenoceptor subtype), was administered into the lateral ventricle (i.c.v.) of rats and plasma growth hormone (GH) levels were measured. Oxymetazoline was more potent to release GH after i.c.v. administration than was clonidine; 0.01 μg i.c.v. oxymetazoline already caused a significant release of GH, while at least 0.1 μg clonidine had to be administered to cause a similar response. The dose-response curve was of an inverted U shape since with 10 μg of oxymetazoline the plasma GH did not rise. When oxymetazoline was injected i.c.v. to rats with somatostatin fibres to the median eminence transected by an anterolateral cut in the hypothalamus there was a significant rise in plasma GH, suggesting that oxymetazoline stimulated GHRH rather than inhibited somatostatin release. Pretreatment with CH-38083 (7,8-(methylenedioxy)-14-α-hydroxy-alloberban HCl, selective for α2-adrenoceptors but not differentiating between α2A and α2B subtypes), prevented the plasma GH rise normally elicited by 1 μg i.c.v. oxymetazoline. The α2A- and α1-selective adrenoceptor antagonist, WB-4101 (2-(2,6-dimethoxyphenoxyethyl)-aminomethyl-1,4-benzodioxane hydrochloride), prevented the GH rise normally induced by oxymetazoline while prazosin, the α2B- and α1-selective adrenoceptor antagonist, prolonged the elevation occurring in the control rats between 30 and 60 min after oxymetazoline injection. Since both prazosin and WB-4101 are α1-adrenoceptor antagonists but differ in their action on α2A and α2B subtypes as well as in their action on oxymetazoline-induced GH secretion, the antagonist studies suggest that oxymetazoline stimulates GH release through activation of α2A-adrenoceptors stimulatory to GHRH release, and not by an action through α2B- or α2C- or α1-adrenoceptors. Since WB-4101 also antagonized clonidine action on GH release we also suggest that the major component may be the stimulation of the α2A-adrenoceptors in the clonidine action on GH release.

Original languageEnglish
Pages (from-to)43-48
Number of pages6
JournalEuropean Journal of Pharmacology
Volume287
Issue number1
DOIs
Publication statusPublished - Dec 4 1995

Fingerprint

Oxymetazoline
Adrenergic Receptors
Growth Hormone
Clonidine
Prazosin
Somatostatin
Hormone Antagonists
Median Eminence
Lateral Ventricles
Hypothalamus

Keywords

  • Clonidine
  • Growth hormone
  • Hypothalamus
  • Oxymetazoline
  • Pituitary
  • α-Adrenoceptor
  • α-Adrenoceptor antagonist
  • α-Adrenoceptor subtype
  • α-Adrenoceptor subtype

ASJC Scopus subject areas

  • Pharmacology
  • Cellular and Molecular Neuroscience

Cite this

Hypothalamic α2A-adrenoceptors stimulate growth hormone release in the rat. / Makara, G.; Kiem, Do T.; Vízi, E.

In: European Journal of Pharmacology, Vol. 287, No. 1, 04.12.1995, p. 43-48.

Research output: Contribution to journalArticle

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