Moderate exercise attenuated airway resistance and inflammation induced by cigarette smoke solution and endotoxin in rats

Abstract

Our aim was to investigate whether exercise would ameliorate the impaired diaphragm muscle function and the inflammation induced by cigarette smoke solution (CSS) and endotoxin in rat lungs. We induced inflammation using intratracheal injections of CSS plus endotoxin in rats. After 2 weeks (day 15), half of these rats (CSS-Run group) began daily treadmill exercise (CSS-Run group) and the other half remained sedentary (CSS group). A third group received intratracheal saline injections and remained sedentary (sham group). Injections continued for 28 days during the study period. To investigate inflammation in the lungs, respiratory function was evaluated and leukocytes were measured. Muscle tension was measured in diaphragm and skeletal muscles, and muscle morphology was histochemically assessed. Compared with the sham group, the inspiratory to expiratory ratios were significantly higher in the CSS group but not in the CSS-Run group. Treadmill exercise increased the percentage of circulating neutrophils. Histology of lungs from the CSS group and the CSS-Run group showed proliferating macrophages; however, aggregation and cell numbers were more remarkable in the CSS group. The peak diaphragm muscle twitch force was significantly higher in the CSS-Run group than in the sham group; additionally, the relative area of fast-twitch glycolytic fibers was more extensive (P < 0.01). We demonstrated that 2 weeks of treadmill exercise improved airway resistance and diaphragm muscle contractile force in rats exposed to repetitive CSS plus endotoxin. We propose that local inflammation was attenuated by aerobic exercise, which increased diaphragm muscle contractility.