A study was conducted to determine whether serum
interleukin-6 (IL-6) activity increased in horses during experimentally induced
endotoxemia and whether serum
IL-6 activity correlated to changes in clinical or laboratory data. Six clinically normal horses were given
endotoxin IV (30 ng/kg of
body weight) in
0.9% NaCl solution over 1 hour. Five of these and 1 additional horse served as controls and were given only
0.9% NaCl solution. Venous blood, for determination of serum
IL-6 activity and WBC count, was collected before and at various times through 8 hours after the start of
endotoxin or NaCl infusion. Rectal temperature and heart and respiratory rates were recorded throughout the study period. Serum
IL-6 activity was determined by bioassay of proliferation of the B13.29 clone B.9 hybridoma cell line. From 1.5 through 5 hours after start of the infusion, serum
IL-6 activity was significantly (P less than 0.05) increased in horses given
endotoxin. Mean peak serum
IL-6 activity was observed between 3 and 4 hours. In response to
endotoxin infusion, horses became lethargic, tachycardic, and febrile.
Leukopenia developed by 1 hour, followed by
leukocytosis at 8 hours. Significant (P less than 0.05) positive association and linear correlation were apparent between mean serum
IL-6 activity and mean rectal temperature in the group of horses that were given
endotoxin. Changes from baseline were not evident in any of the clinical or laboratory values in horses given only NaCl
solution.