PRIOR EXERCISE SUPPRESSES THE PLASMA TUMOR-NECROSIS-FACTOR RESPONSE TO BACTERIAL LIPOPOLYSACCHARIDE

This study was initiated to determine the effect of physical exercise on the in vivo tumor necrosis factor-alpha (TNF) response to Escherichia coli lipopolysaccharide (LPS). Rats familiarized with treadmill running and surgically implanted with vascular catheters were either not exercised or exercised to near exhaustion (mean run time of 102 +/- 13 min) before intravenous LPS challenge (1 mg/kg; lethality of dose is 10-20% in 24 h). Compared with time-matched nonexercised control rats, exercised rats had increased heart rates, plasma lactate, and plasma corticosterone and decreased plasma glucose at the conclusion of exercise. In response to LPS, both groups became hypotensive, exhibited transient hyperglycemia, and sustained hyperlactacidemia. By 30 min post-LPS, plasma corticosterone levels were similar in the two groups. Nonexercised rats exhibited a normal plasma TNF response to LPS with the peak value (10,400 +/- 2,000 U/ml) occurring 90 min after LPS challenge. In contrast, the TNF response in rats exercised before LPS administration was blunted to 17% of the nonexercised group, with the peak occurring at an earlier time after LPS. Addition of recombinant murine TNF to postexercise plasma was fully expressed. The TNF response remained attenuated when LPS was administered up to 6 h after completion of exercise, but it returned to normal in rats allowed to recover for 24 h. The results demonstrate that exercise, perhaps as a stress modality, markedly suppresses the systemic TNF response that is normally observed in response to LPS challenge.