Alpha-adrenergic agonists are a class of sympathomimetic agents that selectively stimulates alpha adrenergic receptors.
There are 2 classes of alpha-adrenergic receptors: subclasses α1 and α2.
Alpha 2 receptors are associated with sympatholytic properties.
Alpha-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.
α1 stimulates the membrane bound enzyme phospholipase C.
Activation of 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.
Alpha adrenergic agonist drug class:
Phenylephrine
Norepinephrine (noradrenaline)
Alpha-1 adrenergic receptor agonist
α1 agonist: stimulates phospholipase C activity with vasoconstriction and mydriasis; used as vasopressors, nasal decongestants and during eye exams
Methoxamine
Midodrine
Metaraminol
Phenylephrine
Amidephrine
Alpha-2 adrenergic receptor agonists inhibits adenylyl cyclase activity, reduces brainstem vasomotor center-mediated CNS activation, used as antihypertensive, sedative & treatment of opiate dependence and alcohol withdrawal symptoms.
Clonidine
Dexmedetomidine
Fadolmidine
Guanfacine,
Guanabenz
Guanoxabenz
Guanethidine
Xylazine
Tizanidine
Medetomidine
Methyldopa
Methylnorepinephrine
Norepinephrine
amitraz
Detomidine
Lofexidine,
Medetomidine
Nonspecific agonists act as agonists at both alpha-1 and alpha-2 receptors.
Xylometazoline
Oxymetazoline
Apraclonidine
Cirazoline
Epinephrine
The following agents are also listed as agonists.
ergotamine
etilefrine
indanidine
mephentermine
metaraminol
methoxamine
mivazerol
naphazoline
norfenefrine
octopamine
phenylpropanolamine
propylhexedrine
rilmenidine
romifidine
synephrine
talipexole
Alpha-adrenergic agonists, are used in the treatment of glaucoma by decreasing the production of aqueous fluid by the ciliary bodies of the eye and also by increasing uveoscleral outflow.
Clonidine and dexmedetomidine target pre-synaptic auto receptors, decreasing norepinephrine which clinically can cause effects such as sedation, analgesia, lowering of blood pressure and bradycardia.