Pathogenesis of fever in a rat burn model: the role of cytokines and lipopolysaccharide.

We investigated the possible causal relationship between interleukin-6 (IL-6) and increased body temperature (T(B)) in a rat burn model. Transmitters for measuring core temperature and estimating activity were implanted in the abdominal cavity. Animals in the burn group were clipped and received full-thickness scald burns to 45% to 55% of the body surface area, and control animals were clipped. T(B) and activity were measured continuously through the tenth postburn day. Carotid lines were placed, and serial blood samples obtained for lipopolysaccharide, IL-6, and tumor necrosis factor-alpha assay. From the third through the tenth postburn day, the burn group had a consistently significantly higher T(B) during light hours than the control group did (average, 0.45 degrees C +/- 10 degrees C, p = 0.0001). Differences in activity during light hours were not significant between the two groups, therefore, do not account for the observed significant difference in T(B). The average IL-6 serum levels were 3.5-fold higher for the burned animals. In this study, burn and control serum levels of IL-6 demonstrated positive correlation with T(B). These data suggest, but do not prove, a causal relationship between IL-6 and fever in the rat burn model, and make it unlikely that circulating systemic lipopolysaccharide is the cause.