Insulin treatment increases skeletal muscle fibre area in patients with diabetes mellitus type 2

The effects of insulin treatment on skeletal muscle characteristics were studied in 18 patients (62 +/- 11 years) with poorly controlled diabetes mellitus type 2 (mean duration 7.5 +/- 6 years). Skeletal muscle biopsy samples were taken from the lateral portion of the quadriceps muscle before and after a period of insulin treatment of 40 +/- 14 days. Enzyme activities (phosphofructokinase, 3-hydroxyacyl-CoA dehydrogenase, citrate synthase, lactate dehydrogenase and creatine kinase) and myoglobin content were assessed. In a subgroup of 11 patients (60 +/- 11 years), skeletal muscle fibre type composition (type I, IIA, IIB and IIC) and fibre type cross-sectional area were also analysed. Following insulin treatment there were 32 and 38% increases, respectively, in the cross-sectional areas of type IIA and IIB fast-twitch fibres (P < 0.02). The fibre type distribution did not change. The myoglobin content in muscle decreased by 20% (P < 0.01). Of the enzymes tested, the 3-hydroxyacyl-CoA dehydrogenase activity decreased by 10% (P < 0.04). Serum glucose, HbA1(C) and serum triglyceride levels decreased (P < 0.001) and body weight and arm muscle circumference increased (P < 0.02). In conclusion, insulin treatment of patients with poorly controlled non-insulin-dependent diabetes mellitus increased the fast-twitch fibre area, reduced myoglobin levels and decreased muscle enzyme activity related to fatty acid oxidation.