Differing Responses of Satellite Cell Activity to Exercise Training in Rat Skeletal Muscle

[Purpose] The present study examined satellite cell and hepatocyte growth factor (HGF) responses to exercise intensity in the rat soleus muscle. [Methods] HGF levels assessed during postnatal growth of the gastrocnemius muscle. Depression of HGF levels occurred up to postnatal week 4, so 4-week-old rats were used the exercise training experiment. Rats walked or ran at speeds of 16 or 24 m/min, at -16% grade, 30 min/trial. Soleus muscles were removed after 72 h. Animals were injected with the thymidine analogue 5-bromo-2'-deoxyuridine (BrdU) 1 h before sampling. The right soleus muscle was used for immunofluorescence, and the left soleus muscle was used to measure HGF protein levels. [Result] HGF levels were unchanged, although numbers of BrdU-positive nuclei increased 2.4-fold in rats with exercise training. [Conclusion] The relationship between activation of satellite cells and HGF production after exercise training remains unclear. However, this study indicates the exercise intensity necessary to activate satellite cells. In the future, this result may facilitate the creation of exercise training intensity as an index of satellite cell activity for muscle strength training.