THE RELATIONSHIPS AMONG IGF-1, DNA CONTENT, AND PROTEIN ACCUMULATION DURING SKELETAL-MUSCLE HYPERTROPHY

Insulin-like growth factor-1 (IGF-I) is known to have anabolic effects on skeletal muscle cells. This study examined the time course of musc le hypertrophy and associated EGF-1 peptide and mRNA expression. Data were collected at 3, 7, 14, and 28 days after surgical removal of syne rgistic muscles of both normal and hypophysectomized (HX) animals. Ove rloading increased the plantaris (Plant) mass, myofiber size, and prot ein-to-body weight ratio in both groups (normal and HX; P < 0.05). Mus cle IGF-1 peptide levels peaked at 3 (normal) and 7 (HX) days of overl oading with maximum 4.1-fold (normal) and 6.2-fold (HX) increases. Inc reases in muscle IGF-I preceded the hypertrophic response. Total DNA c ontent of the overloaded Plant increased in both groups. There was a s trong positive relationship between IGF-1 peptide and DNA content in t he overloaded Plant from both groups. These results indicate that ii t he muscles from rats with both normal and severely depressed systemic levels of EGF-1 respond to functional overload with an increase in loc al IGF-1 expression and 2) this elevated IGF-1 may be contributing to the hypertrophy response, possibly via the mobilization of satellite c ells to provide increases in muscle DNA.