title: Effect of systemic alpha-2 adrenergic blockade on the morning increase in platelet aggregation in normal subjects.
abstract: To assess whether activation of platelets by catecholamines contributes to the increase in platelet aggregation associated with either the assumption of upright posture or exercise, we studied the effect of oral yohimbine on these phenomena. Whole blood platelet aggregation and plasma catecholamine levels were measured before and after standing and at peak exercise in untreated normal subjects and after oral yohimbine. Neurochemical indexes indicated systemic alpha2-receptor blockade by yohimbine. Yohimbine reduced the orthostatic increase in platelet aggregation response by 63+/-11%, but exercise-induced increase in aggregation was unaffected. Thus, alpha2-adrenergic blockade attenuates the orthostatic increase in platelet aggregation. Agents designed to inhibit the morning surge in catecholamine levels or block platelet alpha2 adrenoceptors may reduce the risk of thrombotic vascular events in atherosclerosis.
authors.affiliation: Cardiology Branch, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, Maryland 20892-1650, USA.
authors.forename: N P
authors.initials: NP
authors.lastname: Andrews
authors.forename: D S
authors.initials: DS
authors.lastname: Goldstein
authors.forename: A A
authors.initials: AA
authors.lastname: Quyyumi
mesh_terms: D058669:Adrenergic alpha-2 Receptor Antagonists; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology*; D000328:Adult; D001772:Blood Cell Count / Q000187:drug effects; D001794:Blood Pressure / Q000187:drug effects; D002395:Catecholamines / Q000097:blood*; D002940:Circadian Rhythm; D015986:Confounding Factors, Epidemiologic; D015444:Exercise; D006339:Heart Rate / Q000187:drug effects; D006801:Humans; D008297:Male; D010974:Platelet Aggregation / Q000187:drug effects*; D011187:Posture; D012016:Reference Values; D015016:Yohimbine / Q000494:pharmacology*
chemical_list: D058669:Adrenergic alpha-2 Receptor Antagonists; D000317:Adrenergic alpha-Antagonists; D002395:Catecholamines; D015016:Yohimbine