In order to evaluate possible differences between men and women with regard to the ability of insulin to induce vasodilatation, promote glucose uptake and enhance endothelium-dependent vasodilatation, 12 young (22-28 years), non-obese women and 15 corresponding males were subjected to 2h of euglycaemic hyperinsulinaemia (insulin infusion rate of 56m-unitsċmin-1ċm-2). Forearm blood flow was measured by venous occlusion plethysmography. Endothelium-dependent vasodilatation was evaluated by the local intra-arterial infusion of methacholine into the brachial artery (2-4μg/min). The cardiac index was measured by thoracic bioimpedance. A 2h period of hyperinsulinaemia increased the plasma insulin concentration to a similar degree in both sexes (females, 84±8.8m-units/l; males, 87±7.5m-units/l), but induced a more marked increase in forearm blood flow in females than in males (+104±67% and +52±30% respectively; P < 0.01; 95% confidence interval for difference 11-94%). Furthermore, a significant decrease in total peripheral resistance (-20±6.9%; P < 0.01) and an increase in cardiac index (+23±13%; P < 0.01) were seen in women only (P < 0.05 compared with men). Blood pressure and heart rate were not altered in either sex. Whole-body insulin-mediated glucose uptake and forearm glucose uptake did not differ between the sexes, and the ability of insulin to enhance endothelium-dependent vasodilatation (+19%; P < 0.01) was similar in men and women. In conclusion, the present study shows that the ability of insulin to cause vasodilatation was greater in non-obese young women compared with men. However, no differences between the sexes were seen with regard to insulin-mediated glucose uptake and the ability of insulin to enhance endothelium-dependent vasodilatation.

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