Oxidative state and histological changes in muscles of mastication after conditioning training

Stress due to endurance training of striated muscles leads to adaptive chan ges in the distribution of muscle fiber types (i.e. ratio of type I and typ e II fibers). Moreover, severe training leads to tissue hypoxia and oxidati ve stress in muscles. In the current study, we examined the relationship be tween histological changes and oxidative state in muscles of mastication du ring the acute adaptation phase to a sustained muscle load. Six domestic pi gs received build-ups on the molar teeth in order to induce a sustained loa d of the muscles of mastication for a duration of four weeks. Afterwards th e masseter (M1, M2, M3), medial pterygoid (PM), temporal (TP1, TP2), and ge niohyoid muscles (GH) were removed and the fiber type distribution was dete rmined by enzyme histochemistry. Additionally, the tissue content of glutat hione and lipid peroxidation (LPO) products were measured. The above treatm ent led to muscle fiber transformation of type II into type I (MI, M2, TP2, PM) and a decrease of the GSH content (M1, M2 and TP2). The changes in the GSH/GSSG ratio were in accordance with the changes in proportions of muscl e fiber types, with the lowest GSH/GSSG ratios in the most stressed muscles of the treated animals. No significant changes in LPO products were found. The decrease of the GSH/GSSG ratio in the most stressed muscles indicates a n increased intracellular oxidative stress, which may be caused by tissue h ypoxia during the chronic phase of muscle adaptation.