We examined age-related changes in functional, morphological and metabolic adaptations of the rat diaphragm muscle to compensatory increased activity. Forty-two male Wistar rats (6, 48 and 100 weeks after birth) were randomly divided into control (CTL) and compensatory activation (CAC) groups (n=7 in each group). In the CAC group, denervation surgery in the hemidiaphragm was performed to induce compensatory activation on the contralateral hemi-diaphragm muscle. Four weeks later (10 weeks, 1 year and 2 years after birth), isometric contraction properties by in-vitro physiological measurement, fiber type composition and metabolic properties (succinic dehydrogenase (SDH), 3-hydroxyacyl-CoA dehydrogenase (HAD) and phosphofructkinase (PFK)) were analyzed by histochemical and biochemical procedures.
In the CTL groups, significant prolongations in the contraction and half-relaxation times were found in 2-year group, as compared to 10-week group. This age-related changes were attributed to changes in muscle fiber type composition; selective hypertrophy in Slow-twitch Oxidative fiber. In 2-year CAC group, as compared to age matched CTL group, significant improves were found in the half-relaxation time, SDH activities in each fiber type, HAD and PFK activities of the diaphragm muscle.
These results demonstrated that the aged diaphragm muscle has a tendency toward slow muscle in functional and morphological properties, and that the muscle has a high adaptability to compensatory increased activity, at least in metabolic properties.