Endotoxin receptor site. II. Specificity of endotoxin receptor of platelets and sensitivity to endotoxin in vivo

The biological specificity of the endotoxin receptor on platelet membranes was examined. The binding indices of platelets in experimental endotoxemia which was induced by intravenous administration of endotoxin (Lipopolysaccharide of E. coli, Difco) to rabbits were found to be 30% of the control at 60 min after the injection. The result suggests that the endotoxin receptor of platelets was already occupied. The binding indices of human platelets were measured after pretreatment with pharmacologically active substances which were assumed to effect platelet activity. The binding of LPS to platelets showed competitive inhibition at pharmacologically effective doses, but other substances merely inhibited platelet activity. One interpretation is that there is a common receptor on platelet cell membranes for lipopolysaccharide of E. coli and endotoxin. The sensitivity to endotoxin in vivo and binding indices of platelets were examined in rabbits and guinea pigs since their response to endotoxin is almost opposite with regard to sensitivity. The binding indices of platelets from rabbits and guinea pigs showed a positive correlation with the endotoxin sensitivity. Those findings indicate that platelets play a key role in vivo in the clinical course of endotoxemia.