Effects of childhood exercise and detraining on skeletal muscle mitochondrial metabolism in young OLETF rats

Abstract

【Background and purpose】Long-term childhood exercise prevents obesity not only during exercise period but also during adulthood after detraining period. However, it is unclear why the effects of childhood exercise persist into adulthood. The purpose of this study was to clarify why obesity was controlled after quitting exercise, focusing on mitochondrial metabolism in the skeletal muscle. 【Methods】Four-week-old male Otsuka Long-Evans Tokushima Fatty (OLETF) rats were randomly divided into a sedentary group (OLETF Sed) and an exercise group (OLETF Ex); they exercised from 4- to 12-week-old and detrained from 12- to 20-week-old. Citrate synthase (CS) and 3-hydroxyacyl-CoA dehydrogenase (β-HAD) activities were measured as enzymatic activity analysis for mitochondrial metabolism in the soleus muscle. Succinate dehydrogenase (SDH) activity was also observed for the histological analysis of the skeletal muscles. 【Results】CS activity in the soleus muscle was significantly higher in the OLETF Ex group than in the OLETF Sed group at 12-week-old; however, there were no significant differences at 20-week-old. There were no significant differences in β-HAD activity between the OLETF Ex and OLETF Sed groups at 12- and 20-week-old. In the OLETF Ex group, many muscle fibers were densely stained with SDH staining at 12-week-old; however, at 20-week-old, there were both densely and lightly stained muscle fibers. 【Discussion】Childhood exercise enhanced enzyme activity related to mitochondrial metabolism in the skeletal muscle; however, this adaptation disappeared in adulthood after the detraining period. Increased mitochondrial metabolism in the skeletal muscle due to childhood exercise may contribute little to preventing obesity in adulthood.