Correlation of clinical and laboratory data with serum tumor necrosis factor activity in horses with experimentally induced endotoxemia.

Serum tumor necrosis factor (TNF) activity was quantitated in 8 horses given an IV infusion of endotoxin (0.03 micrograms of lipopolysaccharide/kg of body weight, from Escherichia coli 055:B5) in 0.9% NaCl solution over 1 hour. Serum TNF activity was likewise measured in 6 horses given only 0.9% sterile NaCl solution at the same rate. The duration of serum TNF activity was determined, and serum TNF activity was correlated with clinical and laboratory changes during the induced endotoxemia. Horses had no serum TNF activity prior to endotoxin administration, but geometric mean serum TNF activity was significantly higher from 1 to 4 hours after the start of the infusion. In response to endotoxin, horses seemed depressed, had signs of mild to moderate abdominal pain, developed tachycardia and fever, and had leukopenia followed by leukocytosis. Association between serum TNF activity and temperature, heart rate, attitude abnormality score, and WBC count of horses given endotoxin was significant. Serum TNF activity had a significant positive linear correlation with attitude abnormality and heart rate and a negative linear correlation with the WBC count during endotoxemia. Geometric mean serum TNF activity peaked approximately 1.5 hours prior to mean peak fever, and these data were significantly correlated. Results of this study suggest that TNF is an important mediator of endotoxemia in horses.