Effects of bacterial endotoxin and platelet activating factor (PAF) on human platelet aggregation in native whole blood

Abstract

The effect of bacterial endotoxins E. coll 0111:B4 or S. minnesota and platelet activating factor (1-O-alkyl-2-acetyl-SN-glycero-3-phosphorylcholine) on platelet aggregation in native whole blood (NWB) were evaluated by impedance aggregometry. In the absence of anticoagulants the patterns of impedance changes associated with aggregation were distinct from those of clotting. Both E. coll 0111:B4 and S. mlnnesota endotoxins shortened the time to clot formation, but impedance changes suggestive of accelerated platelet aggregation were minimal or absent. In contrast, PAF caused an increased impedance, with oscillations characteristic of aggregation, which in some instances was superseded by the smooth impedance change associated with clotting. E. coll 0111:B4 endotoxin blocked aggregation and delayed the onset of clotting after PAF, whereas S. minnesota endotoxln accelerated platelet aggregation by PAF in ten of thirteen experiments. Incubation of E. coll 0111:B4 endotoxin and PAF markedly enhanced aggregation by PAF, whereas the effect of S. minnesota was variable. Although E. coli 0111:B4 and S. minnesota endotoxins accelerated clotting but not platelet aggregation of human NWB In vitro , their Interaction with PAF is complex, depending on the type of endotoxin and individual reactivity. The findings suggest that endotoxin could interact with PAF to significantly augment possible hemorrhagic and/or thrombotic complications of septic shock In humans.