Alpha 2-adrenoreceptor subtypes regulate ACTH and beta-endorphin secretions during stress in the rat

Psychoneuroendocrinology. 1999 Apr;24(3):333-43. doi: 10.1016/s0306-4530(98)00081-x.


The effect of different alpha 2-adrenoreceptor subtype agonists and antagonists on adrenocorticotrop hormone (ACTH) and beta-endorphin release induced by ether stress was examined. Ether inhalation-induced ACTH and beta-endorphin increase was inhibited by i.c.v. administration of 30 micrograms but not 1 and 10 micrograms clonidine (alpha 2-adrenoreceptor agonist). I.c.v. oxymetazoline (alpha 2A-adrenoreceptor agonist; 1-10-30 micrograms) or the alpha 1-agonist methoxamine (100 micrograms/rat) failed to inhibit the stress-induced rise. Pretreatment with the alpha 1/alpha 2B.C-antagonist prazosin (0.5 mg/kg, i.p.) prevented the effect of clonidine on the ether stress, while the alpha 1/alpha 2A-antagonist WB-4101 (0.5 mg/kg, i.p.) was unable to counteract the inhibitory effect of clonidine. Prazosin alone had no effect on the ether-induced plasma ACTH and beta-endorphin elevation. These results suggest that noradrenaline in the central nervous system may inhibit the stress-induced hypothalamo-pituitary-axis and pituitary beta-endorphin activation via alpha 2B.C-adrenoceptor subtypes and prazosin may antagonize its effect on these receptors.

MeSH terms

  • Adrenergic alpha-Agonists / pharmacology
  • Adrenergic alpha-Antagonists / pharmacology
  • Adrenocorticotropic Hormone / metabolism*
  • Animals
  • Clonidine / pharmacology
  • Dioxanes / pharmacology
  • Ether / pharmacology
  • Kinetics
  • Male
  • Methoxamine / pharmacology
  • Prazosin / pharmacology
  • Rats
  • Rats, Wistar
  • Receptors, Adrenergic, alpha / physiology*
  • Stress, Physiological / chemically induced
  • Stress, Physiological / physiopathology*
  • beta-Endorphin / metabolism*


  • Adrenergic alpha-Agonists
  • Adrenergic alpha-Antagonists
  • Dioxanes
  • Receptors, Adrenergic, alpha
  • Ether
  • beta-Endorphin
  • Adrenocorticotropic Hormone
  • (2-(2',6'-dimethoxy)phenoxyethylamino)methylbenzo-1,4-dioxane
  • Methoxamine
  • Clonidine
  • Prazosin