Effects of adrenaline on human blood platelets

Abstract

Adrenaline at concentrations too low to cause aggregation of human platelets potentiates the aggregation by ADP. Noradrenaline [norepinephrine] has the same effect but is less active than adrenaline; isopro-pylnoradrenaline is inactive or inhibitory. The potentiation of ADP by catecholamines is blocked by the adrenergic [alpha]-receptor antagonists phentolamine and dihydroergotamine but not by 2-halogenoethylamines or by adrenergic [beta]-receptor antagonists. Both the 1st and 2nd phases of ADP aggregation are potentiated by catecholamines but the 2nd phase more than the 1st. The release from the platelets of adenine nucleotides which is associated with the 2nd phase of aggregation is also increased by adrenaline.