Interleukin-6 production in contracting human skeletal muscle is influenced by pre-exercise muscle glycogen content

1. Prolonged exercise results in a progressive decline in glycogen content and a concomitant increase in the release of the cytokine interleukin-6 (IL -6) from contracting muscle. This study tests the hypothesis that the exerc ise-induced IL-6 release from contracting muscle is linked to the intramusc ular glycogen availability. 2, Seven men performed 5 h of a two-legged knee-extensor exercise, with one leg with normal, and one leg with reduced, muscle glycogen content. Muscle biopsies were obtained before (pre-ex), immediately after (end-ex) and 3 h into recovery (3 h rec) from exercise in both legs. In addition, catheters were placed in one femoral artery and both femoral veins and blood was sam pled from these catheters prior to exercise and at 1 h intervals during exe rcise and into recovery. 3. Pre-exercise glycogen content, was lower in the glycogen-depleted leg co mpared with the control leg. Intramuscular IL-6 mRNA levels increased with exercise in both legs, but this increase was augmented in the ley having th e lowest glycogen content at end-ex. The arterial plasma concentration of I L-6 increased from 0.6 +/- 0.1 ng l(-1) pre-ex to 21.7 +/- 5.6 ng l(-1) end -ex. The depleted leg had already released IL-6 after 1 h (4.38 +/- 2.80 ng min(-1) (P < 0.05)), whereas no significant release was observed in the co ntrol leg (0.36 +/- 0.14 ng min(-1)). A significant net IL-6 release was no t observed until 2 h in the control leg 4. This study demonstrates that glycogen availability is associated with al terations in the rate of IL-6 production and release in contracting skeleta l muscle.