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

Depletion of fat-free mass (FFM) significantly contributes to decreased ske letal muscle weakness and impaired exercise capacity in patients with chron ic 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 w hether there is a role for AAs in the mechanisms for skeletal muscle dysfun ction in COPD, basic knowledge of AA metabolism in the muscle during exerci se is important. We examined the effects of 20 min of exercise on AA metabo lism in 14 patients with COPD and eight control subjects. Arterialized veno us blood and a quadriceps femoris muscle biopsy were obtained before and im mediately after exercise. FFM was not significantly different between the g roups. In COPD, a significant reduction of most muscle AAs was present post exercise, whereas several plasma AAs were increased (p < 0.05). Consequentl y, sum AAs was reduced in muscle (20%; p < 0.01) and increased in plasma (1 6%, 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 alte rs amino acid (intermediary) metabolism in patients with COPD and independe nt of the presence of FFM wasting.