Platelet aggregation in rabbits made tolerant to endotoxin.

Endotoxin may cause abnormal deposition of platelet-endotoxin aggregates, and this event could have damaging effects. We compared the aggregation characteristics of platelets from rabbits made tolerant to the lethal effects of endotoxin with those of platelets from normal rabbits. Platelets from tolerant rabbits aggregated more rapidly (greater than 90 s faster) in the presence of endotoxin than did platelets from nontolerant animals. Furthermore, platelets from tolerant animals aggregated reversibly. These characteristics of platelets from tolerant animals are due to humoral factors in the plasma, because 1:1 dilution of normal platelet-rich plasma with plasma from tolerant rabbits caused the normal platelets to behave like those from tolerant animals. Survival after challenge with lethal quantities of endotoxin was enhanced in tolerant rabbits; this may be due to promotion of more efficient removal of endotoxin-platelet complexes from the blood by the reticuloendothelial system.