Effects Of Eccentric Exercise On Distribution And Expression Of Desmin In Skeletal Muscles Of Rats Under Hypoxic Condition

The purpose of this study was to investigate skeletal muscle injury induced by eccentric exercise from the angle of desmin cytoskeleton and to observe effects of hypoxia on muscle injuries. 128 female SD rats of 7-week old were adopted as the objects of this study and the model of injury for a bout of exhaustive eccentric exercise on a treadmill. The gradient of the treadmill was -16°and the speed was 16m/min. The rats were randomly divided into the hypoxic groups, which was placed in the hypoxic cabin with the PO2 of 12.7%, corresponding to the altitude of 4000m. They were accommodated to this condition for 3 days first, and then they were divided into the hypoxic sedentary control groups (killed on 0,1,2,4,7 days after exercise) and hypoxic exhaustive exercise groups (killed immediately and on 1,2,4,7 days after hypoxic exhaustive exercises). As for the normoxic groups there were one sedentary control group and five exhaustive exercise groups (killed immediately and on 1,2,4, 7 days after a bout of exhaustive exercise). In this study,there were sixteen groups of rats, eight in each group. All the rats in the exercise groups performed exhaustive exercises under normoxic condition.The main results of this study are as follows:(1) After eccentric exercises staining for desmin in part of muscle fibers faded and obscured in different degree and to different extent. It was even lost and negative fibers of desmin occurred, showing that the damage of desmin cytoskeleton is the morphological sign of injuries induced by eccentric exercises. (2) Immunohistochemical staining of desmin was proven to be a tool for estimating the early injury of skeletal muscles. Decrease of desmin staining started immediately after exhaustive eccentric exercise, which was the early representation of injuries and indicated that the muscle fibers would be further injured and become necrosis. The remodeling of part of fibers started on the 4 days after exercise or earlier. During the recovery of injury, the increase of desmin expression is likely to be related to the remodeling of myofibrils.(3) The expression of desmin was mainly regulated at the transcriptional level and the contents of desmin mRNA decreased after eccentric exercise (4) The total activity of calpain in skeletal muscles increased immediately after the eccentric exercise, The activated calpain started to selectively degradate protein substrate, followed by the increase of desmin degradation, the breakdown of desmin filament, the loss of myofibrillar registry, which resulted in the disorder of the Z-line streaming as well as the A-band. In addition, the polypeptide fragments produced by calpain autolysis were likely to become chemoattractant, which was related to the early response of the neutrophils on injuries. (5) Analyzing the influence of hypoxia under the condition of this experiment on injuries induced by eccentric exercises from the aspects of the duration of the downhill running until exhaustion on the treadmill,the expression of desmin and desmin mRNA, the change of the calpain activity, the infiltration of inflammatory cell, it was found that the trends of those changes were basically consistent, showing that the process of the skeletal muscle injuries of rats under the hypoxic condition is consistent with those under the normoxic condition and that the hypoxia is unable to obviously accelerate or deepen the injuries.