Insulin-mediated vasodilation: impairment with increased blood pressure and body mass.

Insulin resistance is associated with hypertension although it is not known if this relationship is casual. Studies have shown that insulin increases skeletal-muscle blood flow despite also increasing sympathetic activity. To determine whether insulin may act as a direct vasodilator and whether insulin-mediated vascular effects are altered in hypertension, we studied insulin-mediated alterations in dorsal-hand-vein compliance in normotensive and mild and borderline hypertensive subjects. In phenylephrine pre-constricted vessels, insulin caused a dose-dependent increase in venous distensibility. Insulin-mediated venodilation was significantly impaired in hypertensive subjects. The vasodilator potency of insulin was significantly correlated with both blood pressure and body mass index. Insulin may be an endogenous vasodilator. Further, in hypertensive and obese subjects, impairment of insulin-mediated vasodilation may contribute to the increase in peripheral resistance characteristic of hypertension.