Quantitative histology and MGF gene expression in rats following SSC exercise in vivo.
OBJECTIVE
We investigated the effects of muscle length during stretch-shortening cycles (SSC) in vivo on changes in MGF gene expression and quantitative morphometry in rat skeletal muscle.


METHODS
Dorsiflexor muscles of male Sprague-Dawley rats were exposed to seven sets of 10 SSC at 500 degrees .s(-1). Animals were randomly assigned to a long muscle length injury group (L-inj), short muscle length injury group (S-inj), or isometric group (Iso), with recoveries examined at 6 or 48 h post-injury for each group. Following exposure, animals were euthanized, and the tissue was prepared for either histology (quantitative morphometry) or RNA isolation, followed by quantitative real-time reverse transcriptase polymerase chain reaction. mRNA levels were measured for mechano-growth factor (MGF), while 18S ribosomal RNA served as the internal reference sample.


RESULTS
Stereological measures indicative of edema and myofiber degeneration were significantly increased in the L-inj SSC group at 48 h when compared with the S-inj or Iso group. MGF mRNA was increased transiently at 6 h in the isometric group. In contrast, MGF mRNA was increased at 48 h in the S-inj, but was not increased at either time point in the L-inj group.


CONCLUSIONS
These data strongly indicate that exposure to SSC at longer muscle lengths result in greater morphometric indices of inflammation and degeneration than SSC conducted at a shorter muscle lengths or isometric contractions, at the same time that the adaptation to SSC was prolonged and, apparently, not resolved in the L-inj group that was manifested by the lack of up-regulation in MGF mRNA.
National Institute for Occupational Safety and Health, Health Effects Laboratory Division, Morgantown, WV, USA.
Brent A
BA
Baker
K M K
KM
Rao
Robert R
RR
Mercer
Ken B
KB
Geronilla
Mike L
ML
Kashon
Gerald R
GR
Miller
Robert G
RG
Cutlip
D000818:Animals; D015870:Gene Expression / Q000235:genetics*; D007537:Isometric Contraction / Q000502:physiology*; D008297:Male; D009141:Musculoskeletal System / Q000293:injuries* / Q000503:physiopathology; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D017207:Rats, Sprague-Dawley; D014903:West Virginia
D012333:RNA, Messenger