Relaxing Factor in Extracts of Blood Platelets and its Function in the Cells

Abstract

THE known release of 5-hydroxytryptamine from blood platelets exposed to thrombin¹ has led to further investigations in this laboratory concerning the mechanism of action of the enzyme on the cells. Recently published results of these investigations² show that a number of intracellular constituents, including 5-hydroxytryptamine, are simultaneously released from the cells through the operation of a sequential reaction system for which the term ‘release reaction of the platelets’ was suggested. In this process a proteolytic reaction catalysed by thrombin represents the first step. It is followed by a reaction which requires calcium ions. Observations indicate that the final step consists in active contraction of the platelet, by which water and solutes are extruded into the surrounding medium.