Abstract
Muscle hypertrophy induced by functional overload (FO) provides an in vivo model to study muscle growth. Glutamine has been shown to improve muscle function, maintain contractile protein levels, and reduce inflammation; however, its effects during muscle growth is unclear. PURPOSE: These experiments tested the hypothesis that glutamine supplementation positively impacts the skeletal muscle response to a growth stimulus as evidenced by greater hypertrophy, increased growth factor levels, and improved contractile function compared to placebo. METHODS: Mice underwent FO of the plantaris or sham surgery. In vivo plantaris force and fatigue resistance (% of maximal force after 10 contractions) were measured 14 days after FO or sham in mice receiving daily glutamine (1 g/kg body mass) or placebo (n= 7-9/group). Insulin-like growth factor 1 (IGF-1) was measured in the plantaris by ELISA after 14 days of FO or sham. Data were analyzed with 2-way ANOVAs. RESULTS: FO increased plantaris mass independent of treatment; however, glutamine tended to enhance muscle hypertrophy compared to placebo (Placebo: 15 ± 0.6 vs. 28 ± 2 mg and Glutamine: 16 ± 0.5 vs. 34 ± 3 mg, for sham and FO, respectively, p<0.05). Maximal isometric force relative to body mass was unchanged with FO, independent of glutamine. Fatigue resistance was increased with FO compared to sham, independent of glutamine (Placebo: 39 ± 4 vs. 50 ± 5% and Glutamine: 33 ± 2 vs. 56 ± 2%, for sham and FO, respectively, p<0.05). Muscle levels of IGF-1 were significantly increased with FO, independent of glutamine (Placebo: 55 ± 7 vs. 848 ± 131 pg/mg protein and Glutamine: 25 ± 10 vs. 813 ± 174 pg/mg protein, for sham and FO, respectively, p<0.05). CONCLUSIONS: Functional overload was associated with significant hypertrophy, elevated IGF-1 levels, and increased fatigue resistance, but these adaptations were not enhanced with glutamine supplementation. Supported by Iowa Space Grant Consortium Undergraduate Research Award
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