Thromboxane A2 biosynthesis during endotoxin-induced aggregation of platelets from normal and sensitized guinea-pigs.

Endotoxin lipopolysaccharides Escherichia coli O26:B6 and E. coli O127:B8 were weak inducers of aggregation in normal guinea-pig platelet-rich plasma (PRP), even in the presence of Ca2+. Indomethacin hardly inhibited endotoxin-induced aggregation, indicating that biosynthesis of thromboxane A2 (TXA2) was of little importance. In accordance with this conclusion TXA2 was not detectable by means of bioassay during endotoxin-induced aggregation in normal guinea-pig PRP. Pretreatment of the guinea-pigs with endotoxin sensitized their PRP to endotoxin. This was due to a humoral factor with a selectively directed towards the polysaccharide moiety of endotoxin. The combination of this factor with endotoxin indued a marked biosynthesis of TXA2 and concomitant platelet aggregation.