title: Resistance exercise alters MRF and IGF-I mRNA content in human skeletal muscle.
abstract: Increasing evidence suggests that the myogenic regulatory factors (MRFs) and IGF-I have important roles in the hypertrophy response observed after mechanical loading. We, therefore, hypothesized that a bout of heavy-resistance training would affect the MRF and IGF-I mRNA levels in human skeletal muscle. Six male subjects completed four sets of 6-12 repetitions on a leg press and knee extensor machine separated by 3 min. Myogenin, MRF4, MyoD, IGF-IEabc (isoforms a, b, and c) and IGF-IEbc (isoform b and c) mRNA levels were determined in the vastus lateralis muscle by RT-PCR before exercise, immediately after, and 1, 2, 6, 24, and 48 h postexercise. Myogenin, MyoD, and MRF4 mRNA levels were elevated (P < 0.005) by 100-400% 0-24 h postexercise. IGF-IEabc mRNA content decreased (P < 0.005) by approximately 44% after 1 and 6 h of recovery. The IGF-IEbc mRNA level was unaffected. The present study shows that myogenin, MyoD, and MRF4 mRNA levels are transiently elevated in human skeletal muscle after a single bout of heavy-resistance training, supporting the idea that the MRFs may be involved in regulating hypertrophy and/or fiber-type transitions. The results also suggest that IGF-IEa expression may be downregulated at the mRNA level during the initial part of recovery from resistance exercise.
authors.affiliation: August Krogh Institute, Copenhagen Muscle Research Centre, DK-2100 Copenhagen, Denmark.
authors.forename: Niklas
authors.initials: N
authors.lastname: Psilander
authors.forename: Rasmus
authors.initials: R
authors.lastname: Damsgaard
authors.forename: Henriette
authors.initials: H
authors.lastname: Pilegaard
mesh_terms: D000328:Adult; D004032:Diet; D005786:Gene Expression Regulation / Q000502:physiology; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases / Q000378:metabolism; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000096:biosynthesis* / Q000235:genetics*; D008297:Male; D018482:Muscle, Skeletal / Q000378:metabolism*; D017570:MyoD Protein / Q000096:biosynthesis; D018006:Myogenic Regulatory Factors / Q000096:biosynthesis* / Q000235:genetics*; D018008:Myogenin / Q000096:biosynthesis; D010809:Physical Fitness / Q000502:physiology*; D012333:RNA, Messenger / Q000096:biosynthesis* / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014891:Weight Lifting / Q000502:physiology*
chemical_list: C503799:MYOG protein, human; D017570:MyoD Protein; D018006:Myogenic Regulatory Factors; D018008:Myogenin; D012333:RNA, Messenger; C063403:myogenic factor 6; D007334:Insulin-Like Growth Factor I; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases