Inhibition of platelet shape-change by sodium thiamylal

Canine platelets were treated in vitro with sodium thiamylal and allowed to surface activate on glass coverslips. Platelet surface activation was markedly inhibited by sodium thiamylal at concentrations as low as 2 X 10(-4) M and this inhibitory effect was most pronounced after pretreating the platelets for 30 minutes with sodium thiamylal. Treatment with sodium thiamylal prevented spreading platelets from reaching the fully spread stage. Additional experiments demonstrated that sodium thiamylal need not be present in the medium during the activation process in order to exert its effect. Preliminary platelet aggregation studies show sodium thiamylal in the 10(-4) - 10(-3) M range to be capable of inhibiting aggregation induced by adenosine diphosphate.