Insulin-mediated vasodilatation, but not glucose uptake or endothelium-mediated vasodilatation, is enhanced in young females compared with males

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.