Mechanisms of platelet release reaction by macromolecules

Abstract

In order to understand the mechanism by which positively charged polylysine induces platelet release reaction in platelet rich plasma, the effects of neutral macromolecule, dextran, on platelets were studied in the presence or abscence of plasma. In the present study, three types of dextrans (DX 40, DX 250, DX 2000) were tested in platelet rich plasma (PRP) and in washed platelet suspension (WPS) for the ability to cause platelet release reaction and the effect of various inhibitors on the aggregation.We observed that all three types of dextrans could induce platelet aggregation in PRP and WPS, but could not elicit the release reaction not only in WPS but also in PRP. Various inhibitors such as adenosine, aspirin, NEM, PGE1 did not inhibit the platelet aggregation in both systems. Heparin, negatively charged acid mucopolysaccharide, also did not inhibit the dextran-induced platelet aggregation in both systems.Earlier we investigated the effects of polylysine on platelets. The study demonstrated that in platelet rich plasma, polylysine elicited the release reaction of serotonin in contrast to dextran and polylysine formed more tightly packed platelet aggregate than dextran which was inhibited by negatively charged heparin. It was suggested that polylysine induced aggregation more effectively than dextran by reducing the negative surface charge and the possible mechanism by which polylysine elicited the release reaction was the formation of more tightly packed platelet aggregate than that by dextran in the presence of low calcium ion concentration in citrated platelet rich plasma.