title: Characteristics of myogenic response and ankle torque recovery after lengthening contraction-induced rat gastrocnemius injury.
abstract: BACKGROUND
  Although muscle dysfunction caused by unfamiliar lengthening contraction is one of most important issues in sports medicine, there is little known about the molecular events on regeneration process. The purpose of this study was to investigate the temporal and spatial expression patterns of myogenin, myoD, pax7, and myostatin after acute lengthening contraction (LC)-induced injury in the rat hindlimb.
  
  
  METHODS
  We employed our originally developed device with LC in rat gastrocnemius muscle (n = 24). Male Wistar rats were anesthetized with isoflurane (aspiration rate, 450 ml/min, concentration, 2.0%). The triceps surae muscle of the right hindlimb was then electrically stimulated with forced isokinetic dorsi-flexion (180°/sec and from 0 to 45°). Tissue contents of myoD, myogenin, pax7, myostatin were measured by western blotting and localizations of myoD and pax7 was measured by immunohistochemistry. After measuring isometric tetanic torque, a single bout of LC was performed in vivo.
  
  
  RESULTS
  The torque was significantly decreased on days 2 and 5 as compared to the pre-treatment value, and recovered by day 7. The content of myoD and pax7 showed significant increases on day 2. Myogenin showed an increase from day 2 to 5. Myostatin on days 5 and 7 were significantly increased. Immunohistochemical analysis showed that myoD-positive/pax7-positive cells increased on day 2, suggesting that activated satellite cells play a role in the destruction and the early recovery phases.
  
  
  CONCLUSIONS
  We, thus, conclude that myogenic events associate with torque recovery after LC-induced injury.
authors.affiliation: Korea Institute of Sport Science, San223-19, Gongneung-2DongNowon-gu, Seoul 139-242, South Korea.
authors.forename: Hongsun
authors.initials: H
authors.lastname: Song
authors.forename: Eisuke
authors.initials: E
authors.lastname: Ochi
authors.forename: Kihyuk
authors.initials: K
authors.lastname: Lee
authors.forename: Kenji
authors.initials: K
authors.lastname: Hiranuma
authors.forename: Koichi
authors.initials: K
authors.lastname: Nakazato
mesh_terms: D000818:Animals; D000843:Ankle Joint / Q000503:physiopathology*; D001696:Biomechanical Phenomena; D015153:Blotting, Western; D004195:Disease Models, Animal; D006614:Hindlimb; D007150:Immunohistochemistry; D008297:Male; D009119:Muscle Contraction; D024510:Muscle Development; D018482:Muscle, Skeletal / Q000293:injuries* / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology*; D017570:MyoD Protein / Q000378:metabolism; D018008:Myogenin / Q000378:metabolism; D055435:Myostatin / Q000378:metabolism; D051761:Paired Box Transcription Factors / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D020127:Recovery of Function; D012038:Regeneration; D032496:Satellite Cells, Skeletal Muscle / Q000378:metabolism / Q000473:pathology; D013180:Sprains and Strains / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology*; D013997:Time Factors; D019415:Torque
chemical_list: C525913:Mstn protein, rat; D017570:MyoD Protein; C503803:Myog protein, rat; D018008:Myogenin; D055435:Myostatin; C530821:PAX7 protein, rat; D051761:Paired Box Transcription Factors