Intra-arterial infusion of insulin attenuates vasoreactivity in human forearm

Hyperinsulinemia may contribute to the development of hypertension. The aim of the present study was to determine whether hyperinsulinemia modulates vascular reactivity to phenylephrine or angiotensin II. In 10 young, healthy volunteers, the left brachial artery was cannulated for drug infusion and direct measurements of arterial pressure. We measured forearm blood flow by a strain-gauge plethysmograph while infusing phenylephrine (0.2, 0.8, and 2.4 micrograms/min) and angiotensin II (5, 10, and 20 ng/min) locally into the brachial artery before and during simultaneous intra-arterial infusion of insulin (0.15 mU/kg per minute). Forearm vascular resistance was calculated from directly measured arterial pressure and forearm blood flow. Intra-arterial infusion of insulin raised the local plasma insulin level from 10.3 +/- 1.4 to 133.3 +/- 21.1 microU/mL (P < .01) and did not change blood glucose level in the venous effluents of the forearm. Insulin infusion slightly but not significantly increased basal forearm blood flow (4.6 +/- 1.5 to 5.5 +/- 0.9 mL/min per 100 milliliters, NS) and decreased forearm vascular resistance (22.1 +/- 2.1 to 20.3 +/- 2.8 U, NS). Phenylephrine and angiotensin II increased forearm vascular resistance dose dependently before and during simultaneous insulin infusion (P < .01 for both). Intra-arterial infusion of insulin attenuated vascular reactivity to phenylephrine (P < .01) and angiotensin II (P < .01). None of these drugs changed blood pressure or heart rate. Our results suggest that hyperinsulinemia attenuates vascular reactivity in the forearm resistance vessels in healthy humans.