IL-6 and TNF-α expression in, and release from, contracting human skeletal muscle

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Abstract
The aim of the present study was to examine whether IL-6 and TNF-α are expressed in, and released from, human skeletal muscle during exercise. We hypothesized that the skeletal muscle will release IL-6, but not TNF-α, during exercise because of previous observations that TNF-α negatively affects glucose uptake in skeletal muscle. Six healthy, male subjects performed 180 min of two-legged knee-extensor exercise. Muscle samples were obtained from the vastus lateralis of one limb. In addition, blood samples were obtained from a femoral artery and vein. Plasma was analyzed for IL-6 and TNF-α. We detected both IL-6 and TNF-α mRNA in resting muscle samples, and whereas IL-6 increased (P < 0.05) ∼100-fold throughout exercise, no significant increase in TNF-α mRNA was observed. Arterial plasma TNF-α did not increase during exercise. Furthermore, there was no net release of TNF-α either before or during exercise. In contrast, IL-6 increased throughout exercise in arterial plasma, and a net IL-6 release from the contracting limb was observed after 120 min of exercise (P < 0.05).