Effects of streptozotocin diabetes, insulin treatment, and training on the diaphragm

The adaptive capability of the diaphragm, the only skeletal muscle considered a vital organ, has received little investigative attention compared with the limb muscles. Since it is chronically active, we asked whether it will adapt to exercise training and if so to what extent. Metabolic adaptations of the diaphragm to exercise training were studied under three conditions: normal, streptozotocin-diabetic, and diabetic receiving insulin treatment. The activities of hexokinase (HK), phosphorylase, and phosphofructokinase (PFK) in the diaphragm of sedentary diabetic Sprague-Dawley albino rats were 22-36% lower than in normal animals. Insulin treatment returned PFK and HK to normal and above normal, respectively. Tricarboxylic acid cycle marker enzymes were not affected by the diabetic condition or insulin treatment. beta-Oxidation enzyme 3-hydroxyacyl-CoA dehydrogenase (HADH) was 60% higher than normal in the diabetic diaphragm and returned to normal with insulin treatment. Training resulted in increases in the glycolytic and aerobic capacities of all groups. The aerobic changes were similar to those of limb muscles. HADH activity was increased in the normal and diabetic insulin-treated trained groups, but because of its already high activity in the diabetic diaphragm, it did not require an adaptation.