Effects of ONO-6240, a platelet-activating factor antagonist, on endotoxin shock in unanesthetized sheep.

To determine the role of platelet-activating factor (PAF) in endotoxin shock, we studied the effects of ONO-6240, a PAF antagonist, on endotoxin shock in unanesthetized sheep. Changes in hemodynamics, lung lymph balance, leukocyte and platelet counts, and arterial blood gas tensions were measured in four groups; endotoxin alone; endotoxin plus ONO-6240; ONO-6240 alone; vehicle control. Pretreatment with ONO-6240 in sheep given endotoxin significantly prevented the decreases in systemic arterial pressure, left atrial pressure and cardiac output observed in sheep given endotoxin alone. A partial effect on diminishing the magnitude of peripheral leukopenia was also noted. However, pretreatment with ONO-6240 had little effect on pulmonary hypertension and lung lymph balance. We conclude that endotoxin causes two different effects: vascular collapse and direct lung injury; and that PAF is involved only in the circulatory manifestations.