Objective: The purpose of this study was to observe the expression of muscle tumor necrosis factor-α (TNF α) in rat during exercise-induced muscle injury and repair. Methods: The gastrocnemius of 8-week-SD rats were fetched at 0h, 6h, 12h, 1d, 2d, 3d, 1w, 2w after one bout of downhill treadmill running( 90min, -16m/min speed and -16 °slope) for HE staining. Serum and muscle TNF α expression was analyzed by ELISA and immunohistochemistry staining. Results: Skeletal muscle had massive inflammatory cells accumulation and infusion 3d after exercise, then gradually attenuated and vanished at 2w. Serum TNF α contents showed minor changes while the expression of TNF α in muscle elevated significantly throughout the whole process, reaching peaks at 0h and 3d respectively. The positive staining of TNF-a appeared not just in inflammatory cells but also in myofiber endochylema. Conclusion: The higher expression of TNF α during muscle injury and repair course suggested multiple roles of TNF α in inflammatory and regeneration of skeletal muscle.

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