Tumor necrosis factor is not involved in exercise-induced elevation in core temperature.

Female Sprague-Dawley rats (12:12-h light-dark photoperiod) with access to running wheels have an elevated body temperature (BT) both during exercise (nighttime) and nonexercise periods (daytime). We studied whether the exercise-induced increase in BT is modulated by the release of the cytokine, tumor necrosis factor-alpha (TNF). Two weeks after the onset of exercise, nighttime temperatures of exercising rats were elevated approximately 0.5 degree C compared with preexercise values (P = 0.006). By 3 wk after the onset of exercise, daytime temperatures had increased 0.3 degree C (P = 0.03) above control levels. To confirm that endogenously produced TNF can modulate fever in female rats, we injected six rats with antiserum to TNF (300 microliters/rat) and six rats with control serum 24 h before intraperitoneal injection of lipopolysaccharide (50 micrograms/kg). As occurred in earlier studies on male rats, antiserum-treated female rats had significantly enhanced fevers (P = 0.017). To determine whether endogenously produced TNF was involved in modulating the daytime and nighttime increases in BT, antiserum to TNF (300 microliters/rat, n = 7) or control serum (300 microliters/rat, n = 5) was injected intraperitoneally in exercising rats. Neither injection of antiserum nor control serum had any effect on daytime or nighttime BTs. Because BTs of exercising female rats injected with antiserum against TNF were not affected, we conclude that TNF is not responsible for modulating their exercise-induced rise in BT.