Exercise and cytokines with particular focus on muscle-derived IL-6.

Exercise induces increased circulating levels of a number of cytokines. Thus, increased plasma levels of tumour necrosis factor (TNF)-alpha, interleukin (IL-1) beta, IL-1 receptor antagonist (IL-1ra), TNF-receptors (TNF-R), IL-10, IL-8, and macrophage inflammatory protein (MIP)-1 are found after strenuous exercise. The concentration of IL-6 increases up to 100 fold after a marathon race. Recently, it has been demonstrated that IL-6 is produced locally in contracting skeletal muscles and that the net release from the muscle can account for the exercise-induced increase in arterial IL-6 concentration. IL-6 more than any other cytokine is produced in large amounts in response to exercise. It is produced locally in the skeletal muscle in response to exercise, and IL-6 is known to induce hepatic glucose-output and to induce lipolysis. This indicates that IL-6 may represent an important link between contracting skeletal muscles and exercise-related metabolic changes.