Lactate Dehydrogenase Isozymes in Skeletal Muscle of Patients With Chronic Obstructive Pulmonary Disease

Introduction and Objectives: In patients with chronic obstructive pulmonary disease (COPD), lactate dehydrogenase (LDH) levels in skeletal muscles are normal or tend to be elevated; on exercise, these levels increase more rapidly than in individuals without COPD. As it is likely that concentrations of LDH isozymes LDH4 and LDH5 are elevated in such patients, we measured those isozymes in peripheral muscle of patients with COPD. Patients and Methods: Eighteen patients with COPD and 10 healthy nonsmokers were included in the study. Spirometry and the 6-minute walk test were performed, and a biopsy of the quadriceps muscle was taken to measure levels of both total LDH and LDH isozymes by agarose gel electrophoresis and to classify the types of muscle fi bers. Results: Controls and patients had similar concentrations of total LDH (mean [SE], 130 [30] μmol/min/g vs 152 [50] μmol/min/g, respectively) and LDH isozymes. A subgroup of 5 patients showed increased levels of isozymes LDH1, LDH2, and LDH3, with decreased LDH5 levels; these patients were women and had a lower oxygen saturation. The LDH5 level was directly correlated with the 6-minute walk test and oxygen saturation. The percentage of type IIA fi bers correlated directly with LDH3 and LDH4 concentrations whereas type IIX fi bers were inversely correlated with LDH3 concentration. Conclusion: Measurement of LDH isozyme concentrations enabled a subgroup of patients to be identifi ed with a higher concentration of cardiac isoenzymes and lower concentration of muscle isoenzymes, a situation which might indicate adaptation that favors aerobic metabolism.