Metabolic enzymatic activities in the intercostal and serratus muscles and in the latissimus dorsi of middle-aged normal men and patients with moderate obstructive pulmonary disease.

The glycolytic and oxidative enzyme activities (lactate dehydrogenase (LDH), hexokinase (HK), citrate synthase (CS) and 3-hydroxyacyl-CoA-dehydrogenase (HAD] were measured in the fifth internal and external intercostal muscles, in the vertical and horizontal parts of the serratus, an accessory inspiratory muscle, and in a non-respiratory muscle, the latissimus dorsi (LD) of twenty middle-aged men: nine subjects with normal lung function and eleven patients with moderate chronic obstructive pulmonary disease (COPD). In the normal subjects the enzyme activities of the respiratory muscles were similar to those of the LD, and there were no differences between the internal and the external intercostal muscles. In the COPD patients the metabolic activities of HK, CS and HAD were higher in both intercostals than in LD. Furthermore, there was a significant increase in these enzymatic activities as compared to the intercostals of the normal subjects. These data support the hypothesis that the internal and external intercostal muscles play a more important role in COPD patients than in normal subjects. They are consistent with the hypothesis that COPD has an endurance training effect on both intercostal muscles which could compensate for diaphragmatic disuse.