Insulin Does Not Reduce Forearm «*-Vasoreactivity in Obese Hypertensive or Lean Normotensive Men

Evidence supports the hypothesis that an impaired capacity of insulin to antagonize norepinephrineinduced vasoconstriction increases «-adrenergic tone in overweight young men with insulin resistance and mild hypertension. Therefore, the effects of regionally infused insulin at 100 /iU/mL on forearm blood flow (mllliliters per deciliter per minute) and responses to norepinephrine were measured in seven obese hypertensive and eight lean nonnotenslve men younger than 45 years old. The obese hypertensive men were hyperinsulinemic and insulin resistant compared with the normotensive men, as evidenced by abnormal values for fasting insulin (15.5±1.6 versus 7.2±0.8 /lU/mL, P<.001), the insulin area under the curve in response to a 2-hour oral glucose tolerance test (12.0±1.5 versus 6.7±1.1 mUxmin/dL, /<.01), and the disappearance rate of glucose during a 15-minute insulin tolerance test (2.7±0.3 versus 4.1 ±0.3 mg%/min, P<.05). The logarithm of the norepinephrine ECM was not significantly different in obese hypertensive men (mean, 95% confidence interval: —8.15, -8.42 to —7.87) versus lean normotensive men (-7.91, -8.23 to -7.59). The 2-hour regional insulin infusion at 100 /iU/mL did not significantly alter the ECH for norepinephrine in either group. Insulin at this concentration induced significant and similar increases of forearm blood flow in the hypertensive and normotensive groups (1.7±0.4 versus 1.7±0.6 mL/100 mL per minute, P=NS). At approximately 100 jiU/mL, insulin does not antagonize norepinephrine-induced vasoconstriction in the forearm circulation of either obese hypertensive or lean normotensive men. At this dose, the direct forearm vasodilator actions of insulin, in contrast to indexes of insulin-mediated glucose disposal, are comparatively well preserved in obese young men with mild hypertension. Thus, abnormalities of the regional vascular actions of insulin do not explain the previously reported elevation of forearm vascular or-adrenerglc tone in obese, mildly hypertensive young men. (Hypertension. 1993^2:584-590.)