Regenerating skeletal muscle cells express insulin-like growth factor I

The expression of the trophic peptide insulin-like growth factor I (IGF-I; somatomedin C) was investigated in the regenerating soleus muscle of mice after injury by the snake venom taipoxin. No specific IGF-I immunoreactivity was observed in muscle cells during control conditions. Within 2 days after taipoxin injection, IGF-I immunoreactivity could be demonstrated in activated satellite cells. Myoblasts and myotubes expressed high IGF-I immunoreactivity. The IGF-I immunoreactivity was strictly cytoplasmatic and obviously associated with polyribosomes. No vesicular or membraneous IGF-I immunoreactivity could be demonstrated. It is concluded that IGF-I is synthesized in myogenic cells during skeletal muscle regeneration. It is suggested that IGF-I exerts its effects on skeletal muscle mainly by autocrine mechanisms.