荷重日内頻度がラットヒラメ筋の廃用性萎縮予防に及ぼす影響

Effect of Weight-Bearing Frequency per Day in Retarding Disuse Atrophy in Rat Soleus Muscle

　［要旨］本研究の目的は，総荷重時間を一定にした場合に，1日の荷重頻度の違いが廃用性筋萎縮に及ぼす影響を検索することである．2週間の後肢懸垂法にてラットヒラメ筋の廃用性萎縮を惹起し，荷重は5日/週行った．ウィスター系雄ラット（219±8g，n＝18）を，①懸垂群，②懸垂中1日1回1時間荷重を実施する1回荷重群，③懸垂中，30分荷重を1日2回実施する2回荷重群，および④対照群の4群に分け比較検討した．

　ATPase組織化学的染色・分析の結果，タイプⅠの筋線維断面積は対照群と比較し，1回荷重群が65％，2回荷重群が54％に減少し，各群間に有意差を認めた．タイプⅡ線維では懸垂群（70％）と2回荷重群（71％）間に差がなかった．また，2回荷重群で著明なマクロファージの増加が観察された．筋線維タイプ構成比率は，実験群間に差がなかった．以上より，総荷重時間を一定にした場合，ラットヒラメ筋の廃用性萎縮の進行抑止に関しては，2回荷重より1回荷重が効果的なことが示唆された．

　The purpose of this study was to investigate the effect of weight-bearing frequency per day in preventing disuse muscle atrophy, given a fixed total time of weight-bearing each day. Soleus muscle atrophy was induced by hindlimb suspension for two weeks. One hour of stationary ground support was provided to two groups of rats each day for five days per week. Male Wistar rats(219±8g, n＝18)were assigned to four groups: ① hindlimb suspension only (HS), ② one hour weight-bearing once a day during the period of hindlimb suspension (SG1), ③ a half hour weight-bearing twice a day during the period of hindlimb suspension (SG2), and ④ control conditions.

　Muscle ATPase histochemical staining, followed by morphometrical analysis, demonstrated that cross-sectional area of type Ⅰ fibers in SG1 and SG2 decreased significantly to 65％ and 54％ of control, respectively. Cross-sectional area of type Ⅱ fibers was not significantly differrent between HS (70％)and SG2 (71％). SG2 also showed an increase in macrophages. Percent distribution of muscle fiber type did not differ among the three experimental groups. In terms of retarding the progress of disuse atrophy in the rat soleus for a given amount of total weight-bearing time, the results suggest that doing all of the weight-bearing in one session per day is more effective than dividing the weight-bearing into two sessions.