Alpha-adrenergic agonist

Alpha Adrenergic agonist
Drug class
Skeletal structor formula of phenylephrine, a common nasal decongestant
Class identifiers
Use	Decongestant, Hypotension, Bradycardia, Hypothermia etc.
ATC code	N07
Biological target	Alpha adrenergic receptors of the α subtype
External links
MeSH	D000316

An adrenergic alpha-agonist (or alpha-adrenergic agonists) are a class sympathomimetic agents that selectively stimulates alpha adrenergic receptors. The alpha-adrenergic receptor has two subclasses α₁ and α₂. Alpha 2 receptors are associated with sympatholytic properties. α Adrenergic agonists have the opposite function of alpha blockers. Alpha adrenoreceptor ligands mimic the action of epinephrine and norepinephrine signaling in the heart, smooth muscle and central nervous system, with norepinephrine being the highest affinity. The activation of α₁ stimulates the membrane bound enzyme phospholipase C, and α₂ inhibits the enzyme Adenylate cyclase. Inactivation of adenylate cyclase in turn leads to the inactivation of the secondary messenger Cyclic adenosine monophosphate and induces smooth muscle and blood vessel constriction.

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

α₁ agonist: stimulates phospholipase C activity. (vasoconstriction and mydriasis; used as vasopressors, nasal decongestants and eye exams). Selected examples are:

α₂ agonist: inhibits adenylyl cyclase activity, reduces brainstem vasomotor center-mediated CNS activation; used as antihypertensive, sedative & treatment of opiate dependence and alcohol withdrawal symptoms). Selected examples are:

The following agents are also listed as agonists by MeSH.