Effects of exercise on amino acid metabolism in patients with chronic obstructive pulmonary disease

Depletion of fat-free mass (FFM) significantly contributes to decreased skeletal muscle weakness and impaired exercise capacity in patients with chronic obstructive pulmonary disease (COPD). FFM wasting suggests disturbances in intermediary metabolism, confirmed by data showing profound alterations in the skeletal muscle amino acid (AA) status in COPD at rest. To unravel whether there is a role for AAs in the mechanisms for skeletal muscle dysfunction in COPD, basic knowledge of AA metabolism in the muscle during exercise is important. We examined the effects of 20 min of exercise on AA metabolism in 14 patients with COPD and eight control subjects. Arterialized venous blood and a quadriceps femoris muscle biopsy were obtained before and immediately after exercise. FFM was not significantly different between the groups. In COPD, a significant reduction of most muscle AAs was present postexercise, whereas several plasma AAs were increased (p < 0.05). Consequently, sum AAs was reduced in muscle (20%; p < 0.01) and increased in plasma (16%, p < 0.05), suggesting an enhanced AA release from muscle in COPD during exercise. In the COPD group, the increase in plasma alanine and glutamine was even higher postexercise (61%, p < 0.01 and 21%, p < 0.01, respectively), suggesting enhanced nitrogen efflux. This study shows that exercise alters amino acid (intermediary) metabolism in patients with COPD and independent of the presence of FFM wasting.