eccentric exercise results in a prolonged increase in interleukin-6 and tumor necrosis factor-α levels in rat skeletal muscle

Interleukin-6 (il-6) and tumor necrosis factor-alpha (tnf-α) are well-known cytokines with pro-inflammatory capabilities, and have been shown to be involved in adaptation to exercise as multifaceted myokines. however, the precise role of il-6 and tnf-α during exercise-induced skeletal muscle injury and subsequent repair processes is not fully understood. in this study, il-6 and tnf-α were examined in soleus muscles at the gene and protein levels using in situ hybridization and immunohistochemical staining, respectively, and serum levels of il-6 and tnf-α were determined before and after a 90-min downhill running session in rats. there were no changes in serum levels of il-6 and tnf-α after exercise, but il-6 and tnf-α mrna increased and maintained high expression in muscles for 1–2 weeks after exercise. il-6 and tnf-a mrnas were identified in both the cytoplasm and the nuclei of myocytes, as well as in invading inflammatory cells. il-6 and tnf-α protein mainly distributed in cytoplasm unevenly and had a prolonged expression until 2 weeks after eccentric exercise. our results demonstrate that there is increased il-6 and tnf-α expression in skeletal muscle that is induced by eccentric exercise and that the high expression of il-6 and tnf-α in the long-term phase after eccentric exercise be more involved in the subsequent recovery of damaged muscle.