Alpha-adrenergic agonist

An adrenergic alpha-agonist (or alpha-adrenergic agonist) is a drug that selectively stimulates alpha adrenergic receptors. The alpha-adrenergic receptor has two subclasses α1 and α2.


Although complete selectivity between receptor agonism is rarely achieved, some agents have partial selectivity.

α1 agonists

α1 agonists: stimulates phospholipase C activity. (vasoconstriction and mydriasis; used as vasopressors, nasal decongestants and eye exams). Selected examples are:
* Methoxamine
* Methylnorepinephrine
* Oxymetazoline
* Phenylephrine cite journal |author=Declerck I, Himpens B, Droogmans G, Casteels R |title=The alpha 1-agonist phenylephrine inhibits voltage-gated Ca2(+)-channels in vascular smooth muscle cells of rabbit ear artery |journal=Pflugers Arch. |volume=417 |issue=1 |pages=117–9 |year=1990 |month=September |pmid=1963492 |doi= |url=]

α2 agonists

α2 agonists: inhibits adenylyl cyclase activity. (reduce brainstem vasomotor center-mediated SNS activation; used as antihypertensives, sedatives & treatment of opiate and alcohol withdrawal symptoms). Selected examples are:
* Clonidine (mixed alpha2-adrenergic and imidazoline-I1 receptor agonist)
* Guanfacine,cite journal |author=Sagvolden T |title=The alpha-2A adrenoceptor agonist guanfacine improves sustained attention and reduces overactivity and impulsiveness in an animal model of Attention-Deficit/Hyperactivity Disorder (ADHD) |journal=Behav Brain Funct |volume=2 |issue= |pages=41 |year=2006 |pmid=17173664 |pmc=1764416 |doi=10.1186/1744-9081-2-41 |url=] (preference for alpha2A-subtype of adrenoceptor)
* Guanabenz (most selective agonist for alpha2-adrenergic as opposed to imidazoline-I1)
* Guanoxabenz (metabolite of guanabenz)
* Guanethidine (periferal alpha2-receptor agonist)
* Xylazine,cite journal |author=Atalik KE, Sahin AS, Doğan N |title=Interactions between phenylephrine, clonidine and xylazine in rat and rabbit aortas |journal=Methods Find Exp Clin Pharmacol |volume=22 |issue=3 |pages=145–7 |year=2000 |month=April |pmid=10893695 |doi= |url=]
* Methyldopa


The following agents are also listed as agonists by MeSH. [MeshPharmaList|82000316]
* amidephrine
* amitraz
* anisodamine
* apraclonidine
* brimonidine
* cirazoline
* detomidine
* dexmedetomidine
* epinephrine
* ergotamine
* etilefrine
* indanidine
* lofexidine
* medetomidine
* mephentermine
* metaraminol
* methoxamine
* midodrine
* mivazerol
* naphazoline
* norepinephrine
* norfenefrine
* octopamine
* oxymetazoline
* phenylpropanolamine
* rilmenidine
* romifidine
* synephrine
* talipexole
* tizanidine

Clinical significance

Alpha-adrenergic agonists are used in the treatment of glaucoma by decreasing the production of aqueous fluid by the ciliary bodies of the eye.


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