Searching for effective countermeasures to disuse muscle atrophy

采用尾部悬吊模型，探讨了大鼠肌肉萎缩的机制。我们还评估了在尾部悬吊期间穿插周期性负重作为肌肉萎缩对策的有效性。将6周龄大鼠随机分为4组：悬吊组、悬吊间歇12h/d负重组(S体重12h)、悬吊间歇间歇负重1h/d组(S体重1h/d)、对照组。停药2周。悬吊期结束后，取4组大鼠的指长伸肌和比目鱼肌，进行生理生化分析。总体而言，比目鱼肌的影响比EDL肌肉的影响要深刻得多。无论是从绝对张力(G)还是从每湿重张力(g/mg)来判断，悬浮剂导致比目鱼肌强直性张力降低。这一下降并不完全归因于肌原纤维蛋白含量或浓度的下降。这表明，除肌原纤维蛋白外，其他因素也参与了比目鱼肌强直性张力的降低。悬浮物使比目鱼肌收缩得更快。伴随着肌球蛋白重链(HC)同工酶组成的变化。肌球蛋白Hc2d和2b的新表达增加了Hc2a的百分比表达，降低了Hc1的表达百分比。每天负重1h可部分抑制悬浮诱导的变化。将负重时间延长到每天12小时被证明是一种更有效的对策。

Using tail-suspension model, we investigated the mechanism of muscle atrophy in the rat. We also evaluated the effectiveness of periodic body weight bearing interspersed during tail-suspension as a countermeasure to muscle atrophy. Six-week-old rats were divided into 4 groups ; Suspension, Suspension interspersed with 12hour of weight bearing per day(S with 12 hr WB), Suspension interspersed with 1 hour of weight bearing per day(S with 1 hr WB), Control. Suspension lasted for 2 weeks. At the end of suspension period, the extensor digitorum longus(EDL)and soleus muscles from the 4 groups were removed and subjected to physiological and biochemical analyzes.The results obtained in this study were as follows. Overall effects were much more profound on the soleus than on the EDL muscle. The suspension caused reduction in tetanic tension of the soleus muscle as judged either from absolute tension(g) or from tension per wet weight(g/mg). This reduction was not entirely attributable to a decrease in myofibrillar protein content or concentration. It was suggested that other factors than myofibrillar protein were also involved in the reduction in tetanic tension in the soleus muscle. The suspension made contraction of the soleus muscle faster. This was accompanied by the change in myosin heavy chain(HC) isozyme composition. A novel expression of myosin HC 2d and 2b were observed in addition to increased percentage expression of HC 2a and decreased percentage expression of HC 1. The body weight bearing for 1 hour per day partially suppressed suspension-induced changes. Prolongation of the time of the body weight bearing to 12 hours per day was shown to be a more effective as the countermeasure.