PLATELET-ACTIVATING-FACTOR - ITS EFFECTS IN THE ANESTHETIZED PONY ANDITS ROLE IN THE CHANGES FOLLOWING EQUINE LARGE COLON TORSION

Surgical correction of large colon torsion causes systemic hypotension , tachycardia, fever, thrombocytopenia, and death in ponies that do no t receive supportive therapy. Changes that occur in the colon include vascular congestion, edema, and mucosal necrosis. Potent inflammatory compounds released by the body in response to intestinal ischemia or t o endotoxemia are thought to cause many of these local and systemic ch anges. Clinical application would exist for drugs that could block the actions or release of these compounds. Platelet activating factor is one very potent inflammatory mediator deriving from membrane phospholi pids, that is released following physiologic insults including trauma, hemorrhage, and intestinal ischemia in many species. This compound, w hen administered intravenously to anesthetized ponies, causes systemic hypotension, pulmonary hypertension, cardiac depression, and leukopen ia, changes similar to those following endotoxin administration. Admin istration of the specific PAF antagonist WEB 2086 completely prevented all effects following IV PAF administration to ponies, and also preve nted some of the peripheral cellular responses that follow large colon torsion and reperfusion. The prior administration of WEB 2086 did not modify the cardiovascular depression or morphological changes in the colon that follow large colon torsion. This suggests that it is not a critical mediator in the changes observed.