Decreased blood flow but unaltered insulin sensitivity of glucose uptake in skeletal muscle of chronic smokers

Chronic cigarette smoking is associated with dysfunction of the vascular endothelium. Smokers have also been shown to be insulin-resistant, at least in some studies. Since insulin-induced vasodilation is dependent on endothelial cell nitric oxide (NO) synthesis, we tested the hypothesis that decreased skeletal muscle blood flow causes insulin resistance in smokers. We studied 37 young normotensive normolipidemic nondiabetic men, of which 14 were smokers and 23 lifelong nonsmokers. The groups were similar with respect to age, body mass index (BMI), and maximal oxygen uptake (Vo2max). Basal and insulin-stimulated femoral muscle blood flow was measured using [15O]H2O and insulin-stimulated muscle glucose uptake using [18F]fluoro-2-deoxy-d-glucose ([18F]FDG) and positron emission tomography (PET). Whole-body glucose uptake was measured using the hyperinsulinemic (insulin infusion 5 mU/kg · min)-euglycemic clamp technique. In the basal state, muscle blood flow was 51% lower in smokers (17 ± 3 mL/kg muscle · min) versus nonsmokers (35 ± 17 mL/kg · min, P< .0001). Insulin increased muscle blood flow comparably in both groups; the mean rate of insulin-stimulated blood flow was 30 ± 10 and 55 ± 38 mL/kg · min (P= .049), respectively. Whole-body and skeletal muscle glucose uptake were similar in both groups during insulin infusion. We conclude that muscle blood flow is lower in chronic smokers compared with nonsmokers under both fasting and hyperinsulinemic conditions. The insulin-induced increase in muscle blood flow and insulin-stimulated glucose uptake appear normal, suggesting that the vasodilatory and metabolic effects of insulin are intact in smokers and the reduced muscle blood flow per se does not cause insulin resistance in these subjects.