DIFFERENCES RELATED TO THE PRODUCTION OF ARACHIDONIC-ACID BETWEEN COLLAGEN-STIMULATED AND THROMBIN-STIMULATED HUMAN PLATELETS

The effects of collagen and thrombin on the liberation of free arachid onic acid were investigated in human platelets by fluorometric high-pe rformance liquid chromatography. Collagen induced a concentration-depe ndent increase in the extent of platelet aggregation, as well as an ac cumulation of arachidonic acid in human platelets. By contrast, thromb in effectively provoked a potent aggregation at relatively low concent ration without any accumulation of free arachidonic acid, although the accumulation of arachidonic acid was detected at a high concentration of thrombin ( > 0.1 U/ml) that induced full aggregation. The selectiv e liberation of arachidonic acid was found in thrombin-stimulated plat elets. Non-selective liberation of fatty acids occurred in platelets t hat had been stimulated with a high concentration of collagen (10 mu g /ml), as well as in platelets stimulated with A23187. The net amount o f free arachidonic acid in collagen-stimulated platelets was estimated by use of eicosatetraenoic acid (ETYA), which is an inhibitor of both cyclooxygenase and lipoxygenase. ETYA markedly potentiated the accumu lation of free arachidonic acid in collagen-stimulated platelets witho ut changing the amounts of other fatty acids in the cell.