TNF and serum lipopolysaccharide activity: Based on previous observations that pretreatment with IL-6 decreased the levels of TNF-α, NO and other pro-inflammatory cytokines in a model of endotoxemia in mice [21], we suggest that in our model, the low levels of eNO and TNF-α in the exercised animals could, at least in part, be secondary to the continuous release of IL-6 induced by exercise.