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.

Classes

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

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, (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,
• Methyldopa

Undetermined/unsorted

The following agents are also listed as agonists by MeSH.

• 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.

References

External links