Epinephrine induced platelet aggregation in rat platelet-rich plasma

Epinephrine at even high concentrations neither caused shape change nor aggregation of rat platelets. However, epinephrine induced aggregation in the presence of low (near-threshold) concentrations of collagen at which concentration only platelet shape change was induced without aggregation. The platelet aggregation was also induced by some other catecholamines and clonidine but not by beta -agonist isoproterenol. The aggregatory potencies of R-(-)-isomers, (-)-epinephrine and (-)-norepinephrine were higher than the corresponding desoxy derivatives, epinine and dopamine. In addition, the epinephrine-induced rat platelet aggregation was inhibited by alpha (2)-antagonists, yohimbin and phentolamine, but not by alpha (1)-antagonist prazosin or beta -antagonist propranolol. These results suggested that the epinephrine-induced rat platelet aggregation is occurring through alpha (2)-adrenergic receptors as is the case with human platelets. (C) 2000 Elsevier Science Ltd. All rights reserved.