Antioxidants and mitochondrial respiration in lung, diaphragm, and locomotor muscles: Effect of exercise

Previous studies have shown that exhaustive exercise may increase reactive oxygen species (ROS) generation in oxidative muscles that may in turn impai r mitochondrial respiration. Locomotor muscles have been extensively examin ed, but there is few report about diaphragm or lung. The later is a privile ged site for oxygen transit. To compare the antioxidant defense system and mitochondrial function in lung, diaphragm and locomotor muscles after exerc ise, 24 young adult male rats were randomly assigned to a control (C) or ex ercise (E) group. E group rats performed an exhaustive running test on a mo torized treadmill at 80-85% (V)over dot O-2max. Mean exercise duration was 66 +/- 2.7 min. Lung, costal diaphragm, mixed gastrocnemius, and oxidative muscles (red gastrocnemius and soleus: RG/SOL homogenate) were sampled. Mit ochondrial respiration was assessed in tissue homogenates by respiratory co ntrol index (RCI: rate of uncoupled respiration/rate of basal respiration) measurement. Lipid peroxidation was evaluated by malondialdehyde concentrat ion (MDA) and we determined the activity of two antioxidant enzymes: supero xide dismutase (SOD) and glutathione peroxidase (GPX). We found elevated ba sal (C group data) SOD and GPX activities in both lung and diaphragm compar ed to locomotor muscles (p < .001). Exercise led to a rise in GPX activity in red locomotor muscles homogenate (GR/SOL; C = 10.3 +/- 0.29 and E = 14.4 +/- 1.51 mu mol.min(-1).gww(-1); p < .05), whereas then was no significant change in lung and diaphragm. MDA concentration and mitochondrial RCI valu es were not significantly changed after exercise. We conclude that lung and diaphragm had higher antioxidant protection than locomotor muscles. The ex ercise test did not lead to significant oxidative stress or alteration in m itochondrial respiration, suggesting that antioxidant function was adequate in both lung and diaphragm in the experimental condition. (C) 1999 Elsevie r Science Inc.