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Effects of stretch-shortening cycle-induced muscle injury on gene expression.

Baker-BA; Rao-KMK; Geronilla-KB; Miller-GR; Metheny-R; Kashon-M; Cutlip-RG
Med Sci Sports Exerc 2003 May; 35(5)(Suppl 1):S157
Investigation of gene expression due to contraction-induced injury would be beneficial in elucidating the mechanisms involved in skeletal muscle response and repair. PURPOSE: To investigate the effect of stretch-shortening cycle ROM (range of motion) on gene expression in rats. METHODS: Testing was performed on dorsiflexor muscles of Sprague-Dawley rats in vivo. Animals were randomly assigned to a long ROM group (L-Inj), short ROM group (S-Inj), or isometric control group (CON). The injury protocol consisted of 7 sets of 10 S-S cycles at 500/s. The S-Inj group received S-S cycles between 70-120, whereas the L-Inj group received S-S cycles between 90-140 ankle angle. The CON group received muscle stimulation only at 90. Dorsiflexor muscles were stimulated for 2.8 s each set, and sets were administered at 1-min intervals. Rats were sacrificed at 6 and 48 hours postinjury. Following sacrifice, tissue was excised, weighed, sectioned, quick-frozen, and stored at -80C. Tissue samples were homogenized directly in Lysis buffer, quick-frozen, and stored at -80C until RNA isolation. RNA was isolated, followed by reverse transcription (RT) and polymerase chain reaction (PCR). Changes in the expression (mRNA) of several genes of interest were measured by real-time PCR. RESULTS: No significant differences were found with respect to collagen-III, IL-1[beta], neonatal myosin, desmin, or IGF-1, whereas significant differences were found with MGF (muscle growth factor). MGF displayed a significant treatment-time interaction (p < 0.05). Post-hoc analysis indicated S-Inj at 48 hr was greater than CON at 48 hr (p < 0.05). Also, the S-Inj at 48 h was greater than the S-Inj at 6 hr (p < 0.05). Furthermore, the L-Inj at 6 hr was greater than S-Inj at 6 hr (p < 0.05). CON at 6 hr was greater than CON at 48 hr (p < 0.05). CONCLUSION: Stretch-shortening cycles increased gene expression of MGF but not IGF-1 in this model over time, and also resulted in elevated levels as compared to isometrically exercised controls. MGF is thought to have an autocrine function while IGF-1 has a systemic function.
Injuries; Musculoskeletal-system; Musculoskeletal-system-disorders; Animals; Laboratory-animals; Muscle-tension; Muscle-stress; Mechanical-properties; Muscles; Muscle-tissue; Muscle-function; Genes; Injuries; Muscle-contraction
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Medicine and Science in Sports and Exercise