Viral expression of insulin-like growth factor-I enhances muscle hypertrophy in resistance-trained rats

Abstract

Muscle hypertrophy is the product of increased drive through protein synthetic pathways and the incorporation of newly divided satellite cells. Gains in muscle mass and strength can be achieved through exercise regimens that include resistance training. Increased insulin-like growth factor-I (IGF-I) can also promote hypertrophy through increased protein synthesis and satellite cell proliferation. However, it is not known whether the combined effect of IGF-I and resistance training results in an additive hypertrophic response. Therefore, rats in which viral administration of IGF-I was directed to one limb were subjected to ladder climbing to test the interaction of each intervention on muscle mass and strength. After 8 wk of resistance training, a 23.3% increase in muscle mass and a 14.4% increase in peak tetanic tension (P(o)) were observed in the flexor hallucis longus (FHL). Viral expression of IGF-I without resistance training produced a 14.8% increase in mass and a 16.6% increase in P(o) in the FHL. The combined interventions produced a 31.8% increase in muscle mass and a 28.3% increase in P(o) in the FHL. Therefore, the combination of resistance training and overexpression of IGF-I induced greater hypertrophy than either treatment alone. The effect of increased IGF-I expression on the loss of muscle mass associated with detraining was also addressed. FHL muscles treated with IGF-I lost only 4.8% after detraining, whereas the untreated FHL lost 8.3% muscle mass. These results suggest that a combination of resistance training and overexpression of IGF-I could be an effective measure for attenuating the loss of training-induced adaptations.

β-Hydroxy-β-Methylbutyrate Did Not Enhance High Intensity Resistance Training-Induced Improvements in Myofiber Dimensions and Myogenic Capacity in Aged Female Rats

“…RT was implemented using a ladder climbing apparatus as described by Lee et al (2004). Briefly, the device was 1 m in length at a 75° incline with 1 cm of space between adjacent ladder rails.…”

“…10 g, 15 g, 20 g, or 40 g) to the base of the rat's tail with foam tape and a clip. The RT protocol was adapted from Lee et al (2004), who demonstrated that ladder climbing produced a 23.3% increase in muscle mass following 8 weeks of training. Daily training consisted of 8 total repetitions beginning with one repetition at 70% of maximum weight determined from pre-test (MAX), two repetitions at 80% MAX, two repetitions at 90% MAX, one repetition at MAX, one repetition at MAX plus 20 g, and one repetition at MAX plus 40 g. Two-minute rest intervals were provided between repetitions.…”

Comparative evaluation of IGF-I gene transfer and IGF-I protein administration for enhancing skeletal muscle regeneration after injury

“…[15][16][17] Viral-mediated IGF-I delivery prevents the age-related loss of skeletal muscle function and has been shown to promote skeletal muscle hypertrophy in an additive manner when combined with resistance exercise training. 18,19 Non-viral plasmid-based electroporationassisted IGF-I gene transfer has been shown to enhance skeletal muscle regeneration after laceration injury. 20 Administration of recombinant IGF-I protein has been shown to promote restoration of muscle function after strain or laceration injuries.…”

Terapia gênica, doping genético e esporte: fundamentação e implicações para o futuro

“…Such episode was observed both in animals which were submitted to strength training and sedentary ones. When the extra IGF-1 gene introduction was combined with strength training, hypertrophy and strength development were higher than the ones observed in only strength-trained animals (and not super-expressed IGF-1) and in the ones which only super-expressed IGF-1 (and did not train strength) (13) . Thus, it can be said that the IGF-1 superexpression may boost in great magnitude the muscular responses to physical training, especially in strength training.…”

“…Since it is still in eminently experimental character stage, there are problems in the gene therapy application, being its risks control one of the most important (7)(8)(9)(10)(11) . However, studies in animal models (2,(12)(13)(14)(15) as well as some studies in humans (1,(6)(7)(16)(17)(18)(19) have presented promising results.…”