Alpha-adrenergic agonist

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Alpha-adrenergic agonists are a class of sympathetic agents that selectively stimulate alpha adrenergic receptors. The alpha-adrenergic receptor has two subclasses, α1 and α2. Alpha 2 receptors are associated with sympatholytic properties, while alpha 1 receptors are associated with sympathomimetic 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 for adrenergic receptors. The activation of α1 stimulates the membrane bound enzyme phospholipase C, and 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.