Epinephrine induced platelet aggregation in rat platelet-rich plasma

Epinephrine at even high concentrations neither caused shape change nor agg regation of rat platelets. However, epinephrine induced aggregation in the presence of low (near-threshold) concentrations of collagen at which concen tration only platelet shape change was induced without aggregation. The pla telet aggregation was also induced by some other catecholamines and clonidi ne but not by beta -agonist isoproterenol. The aggregatory potencies of R-( -)-isomers, (-)-epinephrine and (-)-norepinephrine were higher than the cor responding desoxy derivatives, epinine and dopamine. In addition, the epine phrine-induced rat platelet aggregation was inhibited by alpha (2)-antagoni sts, 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 L td. All rights reserved.