[The relationship between insulin resistance and endothelium-dependent vasodilatation in obese subjects]

To study the relationship between insulin resistance and endothelium-dependent vasodilatation function in obese subjects with normal blood glucose, serum cholesterol and blood pressure and to explore the non-traditional risk factors associated with atherosclerosis.

24 euglycemic obese males (OB) and 12 age and sex matched lean controls (Lean) underwent oral glucose tolerance test (OGTT), euglycemic hyperinsulinemia clamp study with an insulin infusion rate of 120 mU/m(2)/min to evaluate the peripheral glucose disposal rate (GDR) in steady-state, brachial artery ultrasound study to assess the endothelium-dependent vasodilation (EDV) and independent vasodilation (EIV), the combined intima-media thickness (IMT) of common carotid arteries examined by high resolution ultrasound, and fasting lipids profile and free fatty acids (FFAs) concentration.

The blood glucose and serum cholesterol levels were all normal in the OB group but the serum FFA and triglyceride concentrations were elevated compared with those of the controls (FFA: 888 microM/l +/- 158 microM/l vs 508 microM/l +/- 137 microM/l, P < 0.05; TG: 1.8 mM/l +/- 0.6 mM/l vs 1.1 mM/l +/- 0.5 mM/l, P < 0.05) The GDR in steady-state was 6.7 mg x min(-1) x kg(-1) +/- 1.4 mg x min(-1) x kg(-1) in the OB group, significantly lower than that of the controls (12.2 mg x min(-1) x kg(-1) +/- 3.1 mg x min(-1) x kg(-1), P < 0.05). In the OB group the flow-mediated dilation of the brachial artery caused by reactive hyperemia (EDV) were impaired and the relaxation time was shorter than that of the controls (P < 0.05) but the EIV was not significantly different between these two groups. There was a significantly positive correlation between GDR and EDV (r = 0.438, P < 0.05). The IMT of common carotid arteries was thicker in the OB group than in the control group (0.50 mm +/- 0.02 mm vs 0.34 mm +/- 0.19 mm).

The endothelium-dependent vasodilation was impaired in obese subjects even though without hyperglycemia, hypercholesterolemia, and hypertension. Traditional cardiovascular risk factors cannot fully account for the increased risk of cardiovascular disease in metabolic syndrome. Elevated circulating FFA concentration, is characteristic of metabolic syndrome, may play a role in endothelial dysfunction.