Alpha agonists

By Steven Lome

Alpha receptor agonists are substances that activate the sympathetic nervous system by stimulation of alpha receptors, similar to the effects of epinephrine and norepinephrine. Alpha receptors are located in smooth muscle including in the arteries. Stimulation of these receptors results in vasoconstriction increasing afterload causing hypertension.

Alpha agonists are used intravenously to increase afterload in the setting of shock (Neosynephrine) or orthostatic hypotension (midodrine). Alpha agonists are also used intranasally as sinus decongestants (pseudoephedrine, oxymetazoline). Most alpha agonists increase the risk of stroke, tachycardia and sudden cardiac death. Addiction to the nasal decongestants is termed rhinitis medicamentosa as cessation of alpha agonists causes a significant rebound effect.

EpinephrineNorepinephrinePseudoephedrine

                 Epinephrine                        Norepinephrine                    Pseudoephedrine