Myogenin, MyoD and IGF-I Regulate Muscle Mass but not Fiber-type Conversion during Resistance Training in Rats

A. F. Aguiar; I. J. Vechetti-Júnior; R. W. Alves de Souza; E. P. Castan; R. C. Milanezi-Aguiar; C. R. Padovani; R. F. Carvalho; M.D P. Silva

doi:10.1055/s-0032-1321895

International Journal of Sports Medicine, Table of Contents

Int J Sports Med 2013; 34(04): 293-301
DOI: 10.1055/s-0032-1321895

Physiology & Biochemistry

Myogenin, MyoD and IGF-I Regulate Muscle Mass but not Fiber-type Conversion during Resistance Training in Rats

Authors

A. F. Aguiar

¹Morphology, Univ Estadual Paulista (UNESP), Botucatu, Brazil
I. J. Vechetti-Júnior

²Morphology, Univ Estadual Paulista, Botucatu, Brazil
R. W. Alves de Souza

²Morphology, Univ Estadual Paulista, Botucatu, Brazil
E. P. Castan

²Morphology, Univ Estadual Paulista, Botucatu, Brazil
R. C. Milanezi-Aguiar

²Morphology, Univ Estadual Paulista, Botucatu, Brazil
C. R. Padovani

³Bioestatística, Universidade Estadual Paulista, Botucatu, Brazil
R. F. Carvalho

²Morphology, Univ Estadual Paulista, Botucatu, Brazil
M.D P. Silva

⁴Instituto de Biociências de Botucatu, Universidade Estadual Paulista Júlio de Mesquita Filho, Morphology, Botucatu, Brazil

Abstract

The purpose of this study was to test the hypothesis that skeletal muscle adaptations induced by long-term resistance training (RT) are associated with increased myogenic regulatory factors (MRF) and insulin-like growth factor-I (IGF-I) mRNA expression in rats skeletal muscle. Male Wistar rats were divided into 4 groups: 8-week control (C8), 8-week trained (T8), 12-week control (C12) and 12-week trained (T12). Trained rats were submitted to a progressive RT program (4 sets of 10–12 repetitions at 65–75% of the 1RM, 3 day/week), using a squat-training apparatus with electric stimulation. Muscle hypertrophy was determined by measurement of muscle fiber cross-sectional area (CSA) of the muscle fibers, and myogenin, MyoD and IGF-I mRNA expression were measured by RT-qPCR. A hypertrophic stabilization occurred between 8 and 12 weeks of RT (control-relative % area increase, T8: 29% vs. T12: 35%; p>0.05) and was accompanied by the stabilization of myogenin (control-relative % increase, T8: 44.8% vs. T12: 37.7%, p>0.05) and MyoD (control-relative % increase, T8: 22.9% vs. T12: 22.3%, p>0.05) mRNA expression and the return of IGF-I mRNA levels to the baseline (control-relative % increase, T8: 30.1% vs. T12: 1.5%, p<0.05). Moreover, there were significant positive correlations between the muscle fiber CSA and mRNA expression for MyoD (r=0.85, p=0.0001), myogenin (r=0.87, p=0.0001), and IGF-I (r=0.88, p=0.0001). The significant (p<0.05) increase in myogenin, MyoD and IGF-I mRNA expression after 8 weeks was not associated with changes in the fiber-type frequency. In addition, there was a type IIX/D-to-IIA fiber conversion at 12 weeks, even with the stabilization of MyoD and myogenin expression and the return of IGF-I levels to baseline. These results indicate a possible interaction between MRFs and IGF-I in the control of muscle hypertrophy during long-term RT and suggest that these factors are involved more in the regulation of muscle mass than in fiber-type conversion.

Key words

muscle hypertrophy - fiber-type - strength training - myogenic regulatory factor - insulin-like growth factor

Full Text

References

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