The response of circulating levels of the interleukin-6/interleukin-6 receptor complex to exercise in young men

The formation of an interleukin-6/IL-6 receptor (IL-6/IL-6R) complex increases the biological activity and half-life of IL-6, with its response to exercise currently unknown. The aim of the present study was to determine the response of circulating levels of the IL-6/IL-6R complex to exercise. Nine healthy male participants performed 1h of cycling exercise at a workload required to elicit 90% lactate threshold. Venous blood samples were taken at rest, immediately post-exercise and after 1.5 h rest. Hemoglobin concentration and hematocrit were measured to estimate changes in plasma volume during exercise. The concentrations of IL-6, sIL-6R and the IL-6/IL-6R complex were measured via ELISA and corrected for changes in plasma volume. A single bout of acute exercise resulted in a 5-fold increase (P<0.05) in IL-6 and a 1.2-fold increase (P<0.05) in sIL-6R immediately after exercise. These returned to baseline at 1.5 h after the cessation of exercise. There was a 2.1-fold increase (P<0.05) in the levels of the IL-6/IL-6R complex post-exercise with levels remaining 1.8 times elevated (P<0.05) after 1.5 h rest. The present study has demonstrated, for the first time, that circulating levels of the IL-6/IL-6R complex are increased in response to acute exercise in young males.