耐力训练对大鼠骨骼肌超微结构的影响

Effects of endurance training on the ultrastructure of skeletal muscle in rats

目的:探讨大鼠骨骼肌对中等负荷耐力训练的适应性变化。方法:实验于2004-02/09在第四军医大学基础部完成。选择健康雄性8周龄Wistar大鼠40只,进行上坡跑中等负荷运动,坡度是+5°。以16m/min的速度持续奔跑45min。每周训练6d,休息1d,持续8周。自由活动组5只设为对照组,不施加干预,饲养笼内自由活动。训练组按训练时间分为1,2,3,4,6,8周6个时间水平。每组分别为4,4,6,6,7,8只。按不同的训练时间水平处死大鼠,取比目鱼肌肌腹,用30g/L戊二醛和体积分数0.1的甲醛固定,苏木精伊红染色,中性树胶封固,光镜观察。每组任选4只大鼠的比目鱼肌制备电子显微镜切片,电镜观察在不同训练阶段大鼠比目鱼肌超微结构的变化。主要观察肌原纤维和肌节排列的规则程度,肌节明带(I带)和暗带(A带)的完整情况与位置关系;Z线异常变化包括Z线流、Z线模糊、Z线扭曲和Z线消失,有上述任何一种情况出现的Z线均算作异常Z线。异常Z线数占被观察Z线总数的百分率即是Z线异常率。每只动物所观察的Z线总数在1500条以上行方差分析。各组间差别用独立样本t检验进行比较。结果:40只大鼠实验过程中无死亡,全部进入结果分析。①对照组肌纤维排列紧密,横切片上纤维大小较一致,呈多角形;在纵切片上可见到清晰、规则的肌横纹,肌核均匀分布在肌纤维周围的肌膜下,无增生、肿胀或固缩。组织间血管形态正常,无破裂;肌外膜无纤维增生。训练组可见程度不一的肌肉空泡变性、颗粒变性和透明样变性等,以3周组明显。可见炎症细胞浸润。②训练组比目鱼肌Z线异常率在训练后开始增加,在第3周达到高峰,后逐渐减少。训练组2,3,4周组比目鱼肌Z线异常率均高于对照组,差异显著(10.8±0.566,15.763±0.537,11.812±1.274,2.713±0.203,P<0.01)。结论:肌肉组织学病理改变提示大鼠比目鱼肌发生运动性肌肉损伤,并在第3周时损伤最重,出现骨骼肌结构相对“薄弱期”。运动4周后,Z线异常率逐渐降低,病理改变逐渐减少。说明肌肉损伤有一个逐渐加重后经修复逐渐减轻的过程。在损伤积累的同时,肌肉表现出良好的适应能力,但适应的机制尚不清楚。

AIM： To investigate the adaptive changes of rats＇ skeletal muscle in the endurance training of medium load. METHODS： The experiment was carried out in the Department of Basic Medicine, the Fourth Military Medical University of Chinese PLA from February to September 2004. Forty healthy male Wistar rats of 8 weeks old were forced to take part in an upward-slope （＋5°） running task of medium load, the rats should kept running at the speed of 16 m per minute for 45 minutes, they were trained for 6 days every week with 1-day rest for 8 continuous weeks. The free activity group was taken as the control group （n=5）, the rats were not given any interventions, they could move freely in the cage. The training group was divided into 6 groups according to the training time at the 1, 2, 3, 4, 6 and 8 weeks, and there were 4, 4, 6, 6, 7 and 8 rats in the groups respectively. The rats were killed according to the different training time. The muscle belly of soleus muscle was taken, fixed with 30 g/L glutaral and formaldehyde （volume fraction was 0.1）, stained with haematine eosin, and sealed with neutral gum. The muscle tissue was observed under light microscope. The soleus muscles of 4 randomly selected rats in each group were taken to prepare sections of electron microscope, the uhrastructural changes of soleus muscles at different training period were observed under electron microscope. The regular arrange degree of myofibril and myotome, the completeness and position of myotome light band （I band） and dark band （A band） were mainly observed, Z-line abnormalities included Z-line flow, Z-line vagueness, Z-line twist and Z-line disappearance, the occurrence of any one of the above conditions was taken as abnormal Z-line. The percentage of the number of abnormal Z-line to the total number of observed Z-line was the abnormal rate of Z-line. The total number of observed Z-line in each rat was above 1500. The analysis of variance was applied. The intergroup difference was compared with the independent sample t test. RESULTS： All the 40 rats were involved in the analysis of results, no one died. ①Observational results of muscle tissue under light microscope： In the control group, the muscle fiber arranged closely, the fibers on the cross section were of uniform size and multi-angle like, and clear and regular striated muscle could be observed on the longitudinal section, muscular nuclear evenly distributed under the sarcolemma around muscle fiber, no hyperplasia, swelling or pyknosis were observed. The vascular forms between tissues were normal, and there was no breakage. There was no fibrous proliferation in epimysium. In the training groups, muscular vacuolation of different degree, granular degeneration and hyaloid degeneration were observed, which were more obvious in the 3-week training group. The inflammatory cell infiltration was observed.② In the training groups, the Z-line abnormal rate of soleus muscle began to increase after training, reached the peak value at the 3^rd week, and then decreased gradually. In the 2, 3, 4-week training groups, the Z-line abnormal rate of soleus muscle were all significantly higher than that in the control group （10.8±0.566, 15.763±0.537, 11.812±1.274, 2.713±0.203, P 〈 0.01）. CONCLUSION： The muscular histopathological changes indicated that there was exercise-induced muscular injury of soleus muscle, which wasthe severest at the 3^rd week, the relative“weak period” of skeletal structure occurred. After exercise for 4 weeks, the Z-line abnormal rate gradually decreased, and the pathological changes gradually reduced. It is indicated that muscular injury has a process of gradual aggravatuib and gradual relief after repair. At the same time of injury accumulation, muscle shows good adaptive ability, but the mechanism was still not clear.