Mechanisms of early and late hypermetabolism and fever after localized tissue injury in rats

Inflammation and localized tissue injury were induced in rats by intramuscular injection of turpentine. This caused rapid and sustained (2-24 h) increases in colonic temperature (T(c); up by 2.5°C) and oxygen consumption (V̇O2; up by 30%) as well as hypophagia (57%). The early responses (0-2 h) were attenuated by anesthesia, C-fiber deafferentation, peripheral but not central injection of a cyclooxygenase inhibitor, or central injection of a neutralizing antibody to corticotropin-releasing factor (CRF). In contrast, the later (18-20 h) changes in T(c) and V̇O2 were unaffected by anesthesia, C-fiber deafferentation, or central injection of a CRF antibody but were inhibited by either peripheral or central administration of a cyclooxygenase inhibitor. β-Adrenoceptor blockade reduced both phases of the response, and brown adipose tissue activity was significantly elevated from 4 to 24 h after turpentine injection. These data suggest that different mechanisms mediate the metabolic response to localized tissue injury, the early phase involving neural mechanisms characteristic of stress and inflammation, whereas the later phase appears to depend on humoral factors that are commonly associated with infection.