Insulin therapy improves endothelial function in type 2 diabetes

A total of 75 in vivo endothelial function tests (intrabrachial artery infu sions of endothelium-dependent [acetylcholine] and -independent [sodium nit roprusside] vasoactive agents) were performed in 18 type 2 diabetic patient s (aged 58+/-2 years, body mass index 28.5+/-0.6 kg/m(2), and fasting plasm a glucose 229+/-11 mg/dL) and 27 matched normal subjects. These tests were performed before and 6 months after combination therapy with insulin and me tformin and before and 6 months after metformin therapy only. Before insuli n therapy, blood flow responses to acetylcholine (15 mu g/min) were signifi cantly blunted in type 2 diabetic patients (7.5+/-0.7 mL . dL(-1) . min(-1) ) compared with normal subjects (11.6+/-0.9 mL . dL(-1) . min(-1), P<0.01). During insulin therapy, the acetylcholine response increased by 44% to 10. 8+/-1.6 mL . dL(-1) . min(-1) (P<0.05). Insulin therapy also significantly increased the blood flow responses to both low and high doses of sodium nit roprusside. We conclude that insulin therapy improves endothelium-dependent and -independent vasodilatation. These data support the idea that insulin therapy has beneficial rather than harmful effects on vascular function.