Alpha-2 blocker
{{Short description|Drugs blocking alpha-2 adrenergic receptors, limited clinical application in humans.}}
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. They are extensively used in veterinary medicine to reverse the effects of alpha-2 agonist drugs used as sedatives, like xylazine, medetomidine and dexmedetomidine. 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.{{cite journal|last=Lemke|first=KA|title=Perioperative use of selective alpha-2 agonists and antagonists in small animals.|journal=The Canadian Veterinary Journal|date=June 2004|volume=45|issue=6|pages=475–80|pmid=15283516|pmc=548630}}
The tetracyclic antidepressants mianserin and mirtazapine are α2 blockers, although their efficacy as antidepressants may come from their activity at other receptor sites.{{citation needed|date=June 2020}}
Mechanistically, α2 blockers increase adrenergic, dopaminergic and serotonergic neurotransmitters and induce insulin secretion, decreasing blood sugar levels.{{citation needed|date=June 2020}}
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.{{citation needed|date=June 2020}} Moreover, reduced microcirculation together with adrenaline supersensitivity in organs such as liver can occur.{{citation needed|date=June 2020}}
Examples
Examples include atipamezole,{{cite journal |vauthors =Haapalinna A, Leino T, Heinonen E |title=The alpha 2-adrenoceptor antagonist atipamezole potentiates anti-Parkinsonian effects and can reduce the adverse cardiovascular effects of dopaminergic drugs in rats |journal=Naunyn-Schmiedeberg's Arch. Pharmacol. |volume=368 |issue=5 |pages=342–51 |date=November 2003 |pmid=14566451 |doi=10.1007/s00210-003-0827-z|s2cid=23897064 }} efaroxan, idazoxan,{{cite journal |vauthors =Chopin P, Colpaert FC, Marien M |title=Effects of alpha-2 adrenoceptor agonists and antagonists on circling behavior in rats with unilateral 6-hydroxydopamine lesions of the nigrostriatal pathway |journal=J. Pharmacol. Exp. Ther. |volume=288 |issue=2 |pages=798–804 |date=February 1999 |pmid=9918591 |url=http://jpet.aspetjournals.org/cgi/pmidlookup?view=long&pmid=9918591}} yohimbine, and rauwolscine, phentolamine.
References
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