Linkage between whole body suspension-induced muscle a trophy and muscle proteolysis in rats

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The purpose of this study is to examine the effect of whole body suspension on skeletal muscle lysosomal cathepsin B and J activities and muscle dipeptide (anserine and carnosine) contents in rats. Six week male Sprague Dawley rats were divided into the control (CON) group and whole body suspended (WBS) group. The rats of the WBS group were maintained under whole body suspension for 10 days. On the morning of the experimental day, slow-twitch muscle (soleus : SOL) and fast-twitch muscle (gastrocnemius : GAS) were isolated and weighed. Adrenal glands, spleen and thymus also were immediately removed and weighed. Muscle lysosomal cathepsin B and J activities were assayed by fluorimetry, and muscle anserine and carnosine contents were analyzed by HPLC method. The relative weight of SOL muscles was 0.67 times (p<0.001) lower in the WBS group than in the CON group, and that of GAS muscle was not changed by WBS. Lysosomal cathepsin B and J activities in SOL muscles were 2.3 times and 2,2 times, respectively, significantly higher in the WBS group than in the CON group. These lysosomal enzyme activities in GAS muscles, however, were not changed by WBS. Carnosine and anserine contents in SOL muscles were 0.56 times and 0.78 times, respectively, significantly lower in the WBS group than in the CON group. However, these dipeptide contents in GAS muscles were not changed by WBS. These results suggest that whole body suspension-induced SOL muscle atrophy in rats may be associated with higher hydrolytic enzyme activity in slow-twitch muscles.