Natural or synthetic Alpha-adrenergic Agonists selectively bind to and activate alpha adrenergic receptors of the sympathetic nervous system, mimicking the actions of natural sympathomimetic neurotransmitters (norepinephrine and related substances). Alpha-adrenergic Agonists can initiate physiological responses such as vasoconstriction, pupil dilation, and contraction of pilomotor muscles. (NCI04)