While the overall benefits of strength/resistance training on skeletal muscles were well documented, the effects of resistance training on the content of insulin-like growth factor-1 (IGF-1) and myostatin is still not clear. Insulin-like growth factor- I (IGF- I) is a positive regulator in proliferation and differentiation of skeletal muscle cells, while myostatin acts as a negative regulator of skeletal muscle mass. The systemic type of IGF-I (IGF-I Ea) and the other IGF-I splice variants-mechano growth factor (MGF) may play a different role in muscle adaptation to resistance exercise. The purpose of this study was to determine the effects of 10 weeks ladder climbing (as a means of resistance exercise) on the mechanism of skeletal muscle' adaptation by studying the changes of IGF-1, IGF-1EamRNA, MGFmRNA, and myostatin mRNA in gastrocnemius of rats.
Method
Twelve male Sprange-Dawley (SD) rats were divided randomly into two groups: 6 in the control group (C) and 6 in the exercise group (E). Exercise group rats took ladder climbing with weights attached to their tails (3 days/week, 6 reps/day) for 10 weeks. The attached weights were increased gradually from 30% to 200% of their body weights, about 20% per week,. The ladder is one meter long and inclined at 85 degrees. The rats in the E-group were sacrificed 48 hours following their last exercise session and so did the rats in the C-group. Their muscle IGF-1 peptide was measured by the immunohistochemistry (IHC), and their IGF-1Ea mRNA, MGF mRNA, myostatin mRNA were measured by the Reverse Transcription-Polymerase Chain Reaction (RT-PCR).
Analysis/Results
After 10 weeks resistance training, the contents of IGF-1 peptide (M±SD: E-group = 24.958±2.172 vs. C-group = 20.900±1.890) and the expression of MGF mRNA (0.351±0.017 vs. 0.222±0.038) increased significantly (p<.05), but the expression of IGF-1EamRNA (0.258±0.075 vs. 0.218±0.040) had no change. In addition, the expression of myostatin mRNA in E-group (0.076±0.030) decreased significantly (p <.05) compared to C-group (0.204±0.064).
Conclusions
The 10 weeks resistance exercise can lead to an increase in IGF-1 content and decrease in the expression of myostatin mRNA. After 10 weeks resistance exercise, the expression of IGF-1Ea has no change, but MGF' expression increased significantly . It seems that MGF may be more sensitive, as well as playing a more important role, in the adaptation to resistance exercise than the IGF-1Ea.