Effects Of Resistance Exercise On The Insulin-like Growth Factor-I,MGF And Myostatin In Skeletal Muscle Of Aging Rats

Age-related loss of muscle mass (sarcopenia) is one of the most marked symptom associated with aging. It's consequences mainly reflected in loss of muscle mass ,muscle size and muscle strength . Muscle has an intrinsic ability to adapt to different types of work by reducing the loss of muscle mass .Exercise can prevent or slow down the aging of muscle. Insulin-like growth factor-I (IGF-I) is a positive regulator in proliferation and differentiation of skeletal muscle cells, while myostatin (MSTN)is a member of transforming growth factor -βsuperfamily that 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) play different role in muscle hypertrophy.24 male SD rats were divided into 4 groups randomly, young control group (YC), young experimental group (YE), aging control group (AC), aging experimental group (AE). The old groups were treated with D-galactose .The rats of experimental group take 10 weeks resistance exercise. The IGF-I peptide were observed by immunohistochemistry(IHC).The level of skeletal muscle IGF- I Ea mRNA,MGF mRNA and muscle satellite cell configuration in rats were observed by RT-PCR and transmission electronmicroscope .Based on all of these ,we try to expound the mechanism of skeletal muscle hypertrophy and regeneration after injury.The results indicated that the contents of gastrocnemius muscle IGF- I peptide and the expression of IGF-I Ea mRNA,MGF mRNA decreased while the expression of myostatin increased. After 10 weeks resistance exercise, the contents of IGF- I peptide and the expression of MGF mRNA increased in both young and aging group ,but the expression of IGF-I EamRNA has no change compared with the resting rats .Muscle satellite cell were observed by transmission elecrtonmicroscope. The results show that the level of muscle satellite cell hyperplasia of exercised rats are signifienatly increased compared with the resting ones.Conclusions: Resistance exercise can prevent or slow down the occur of sarcopenia. MGF and IGF- I Ea splice variants are important factors in muscle repair and regeneration, but they have different function. Firstly , MGF active the satellite cell and enhance the cell proliferation. Secondly, 1GF-I Ea up-regulate the protein synthesis and myoblast fuse to myotubule. In this process, MGF is more efficient than IGF-I Ea. Myostatin is a negative regulator of skeletal muscle formation. Myostatin , sensitively to exercise and age, is an important factor in preventing sarcopenia.