抄録
It is generally accepted that skeletal muscle atrophy is induced by hypokinesia and/or hypodynamia such as bed-rest, gypsum fixation, tenotomy, joint immobilization, suspensions and space-flight. On the other hand, skeletal muscle possessed multiple proteolytic systems, and cathepsin B is known to be one of the lysosomal proteases. Both the increased catabolism and decreased synthesis of protein in the muscles may be causally related to muscle atrophy occurring in suspension. Further, muscle atrophy may release muscle dipeptides, e.g., carnosine (CAR) or anserine (ANS). In the present study, therefore, the effects of whole body suspension (WBS) on the muscle protein, cathepsin B and dipeptide levels in rats were investigated. Male SD (n=24, 7wks old) rats were divided into the cage control (CON) group and WBS group. The WBS was carried out for 10 days. The relative weights of soleus (SOL) and gastrocnemius (GAS) muscles per BW were lower in the WBS than those in the CON. SOL and GAS muscle protein contents in the WBS were clearly lower than those in the CON. SOL muscle cathepsin B activities per BW were significantly higher in the WBS than in the CON. The WBS decreased muscle CAR concentrations in SOL and GAS muscles, and decreased muscle ANS concentrations in SOL muscles, compared with the CON. In conclusion, WBS-induced SOL muscle atrophy may be induced by increased breakdown of muscle proteins and/or decreased muscle buffering capacities. [Jpn J Physiol 55 Suppl:S225 (2005)]
