Alpha-2 blocker

Alpha-2 blockers (or α2 blockers) are a subset of the alpha blocker class of drugs and are antagonists to the α2 adrenergic receptor. They are mainly used in research, having found limited clinical application in human medicine. Alpha-2 blockers increase noradrenaline release.

Uses

Yohimbine, historically used as an aphrodisiac, is sometimes used in veterinary medicine (although now largely replaced by atipamezole) for reversing the effects of α2s such as medetomidine that are used as sedatives during surgery.[1]

The tetracyclic antidepressants mianserin and mirtazapine are α2 blockers, although their efficacy as antidepressants may come from their activity at other receptor sites.

Mechanistically, α2 blockers increase adrenergic, dopaminergic and serotonergic neurotransmitters and induce insulin secretion, decreasing blood sugar levels.

Withdrawal from α2 blockers can be difficult or dangerous as the global downregulation of neurotransmitters may cause symptoms of depression and other neurological problems, and increased blood sugar levels together with decreased insulin sensitivity can cause diabetes. Moreover, reduced microcirculation together with adrenaline supersensitivity in organs such as liver can occur.

Examples

Examples include atipamezole,[2] efaroxan, idazoxan,[3] yohimbine, and rauwolscine, phentolamine.

References
  1. Lemke, KA (June 2004). "Perioperative use of selective alpha-2 agonists and antagonists in small animals". The Canadian Veterinary Journal. 45 (6): 475–80. PMC 548630. PMID 15283516.
  2. Haapalinna A, Leino T, Heinonen E (November 2003). "The alpha 2-adrenoceptor antagonist atipamezole potentiates anti-Parkinsonian effects and can reduce the adverse cardiovascular effects of dopaminergic drugs in rats". Naunyn Schmiedebergs Arch. Pharmacol. 368 (5): 342–51. doi:10.1007/s00210-003-0827-z. PMID 14566451. S2CID 23897064.
  3. Chopin P, Colpaert FC, Marien M (February 1999). "Effects of alpha-2 adrenoceptor agonists and antagonists on circling behavior in rats with unilateral 6-hydroxydopamine lesions of the nigrostriatal pathway". J. Pharmacol. Exp. Ther. 288 (2): 798–804. PMID 9918591.


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