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-α 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° C ± 10° 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.