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Quantitative Histology and MGF Gene Expression in Rats following SSC Exercise In Vivo

BAKER, BRENT A.; RAO, K. M. K.; MERCER, ROBERT R.; GERONILLA, KEN B.; KASHON, MIKE L.; MILLER, GERALD R.; CUTLIP, ROBERT G.

Medicine & Science in Sports & Exercise: March 2006 - Volume 38 - Issue 3 - pp 463-471
doi: 10.1249/01.mss.0000191419.67030.69
BASIC SCIENCES: Original Investigations

Purpose: 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°·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.

Conclusion: 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

Address for correspondence: Robert G. Cutlip, Ph.D., 1095 Willowdale Road, MS L-2027, Morgantown, WV 26505; E-mail: rgc8@cdc.gov.

Submitted for publication February 2005.

Accepted for publication August 2005.

©2006The American College of Sports Medicine