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

• Published in: International journal of sports medicine 2013-04, Vol.34 (4), p.293-301
• Main Authors: Aguiar, A. F., Vechetti-Júnior, I. J., Alves de Souza, R. W., Castan, E. P., Milanezi-Aguiar, R. C., Padovani, C. R., Carvalho, R. F., Silva, M.D P.
• Format: Article
• Language: English
• Subjects: Adaptation, Physiological; Animals; Biological and medical sciences; Fundamental and applied biological sciences. Psychology; Hypertrophy; Insulin-Like Growth Factor I - genetics; Insulin-Like Growth Factor I - metabolism; Male; Muscle Fibers, Skeletal - pathology; Muscle, Skeletal - metabolism; Muscle, Skeletal - pathology; MyoD Protein - genetics; MyoD Protein - metabolism; Myogenin - genetics; Myogenin - metabolism; Physical Conditioning, Animal - methods; Physiology & Biochemistry; Rats; Rats, Wistar; Real-Time Polymerase Chain Reaction; RNA, Messenger - metabolism; Vertebrates: body movement. Posture. Locomotion. Flight. Swimming. Physical exercise. Rest. Sports
• ISSN: 0172-4622; 1439-3964
• DOI: 10.1055/s-0032-1321895

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