title: Sites of action of alpha 2 agonists and antagonists.
abstract: The alpha 2 adrenoceptor is found on central and peripheral neurons, on vascular smooth muscle and on endocrine tissue. Although some investigational drugs have widely varying affinities for these sites, clinically available alpha 2 agonists and antagonists act at all alpha 2 receptors. This report illustrates a strategy for evaluating the relative contributions of both central nervous system vs peripheral and of prejunctional vs postjunctional actions of a new drug by measurement of several alpha 2 receptor-mediated hemodynamic and neuroendocrine responses. Evidence is also provided for a temporal dissociation of pre- and postjunctional alpha 2 responses that may permit selective postjunctional alpha 2 blockade to be of clinical value in the treatment of sympathetically induced reductions of skin blood flow.
mesh_terms: D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology*; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D001808:Blood Vessels / Q000294:innervation; D002490:Central Nervous System / Q000187:drug effects / Q000378:metabolism; D004146:Dioxanes / Q000494:pharmacology; D013006:Growth Hormone / Q000097:blood; D006801:Humans; D019329:Idazoxan; D007328:Insulin / Q000097:blood; D009638:Norepinephrine / Q000097:blood; D051381:Rats; D011942:Receptors, Adrenergic, alpha / Q000378:metabolism; D017981:Receptors, Neurotransmitter / Q000187:drug effects / Q000378:metabolism
chemical_list: D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D004146:Dioxanes; D007328:Insulin; D011942:Receptors, Adrenergic, alpha; D017981:Receptors, Neurotransmitter; D013006:Growth Hormone; D009638:Norepinephrine; D019329:Idazoxan