INSULIN RESISTANCE AND THE EFFECT OF INSULIN ON BLOOD-PRESSURE IN ESSENTIAL-HYPERTENSION

The aim of this study was to investigate the effect of 2 weeks of insu lin administration on blood pressure and to simultaneously measure ins ulin sensitivity and insulin-induced vasodilatation in obese hypertens ive patients. In a prospective, randomized, double-blind, crossover st udy (study 1), 23 obese, untreated, nondiabetic, hypertensive patients received either neutral protamine Hagedorn (NPH) insulin (0.3 U/kg bo dy wt per day) or placebo subcutaneously for 2 weeks (washout period, 2 weeks), Office and 24-hour blood pressure values were measured at th e beginning and end of each treatment period. In an open-label study ( study 2), 8 obese hypertensive patients and 10 healthy control subject s underwent a 3-step hyperinsulinemic, euglycemic glucose clamp (step 1, 0.5; step 2, 2.5; step 3, 5.0 mU.kg(-1).min(-1) [120 minutes each]) . Leg blood flow (LBF) was measured by venous occlusion plethysmograph y. Insulin administration decreased mean+/-SD office blood pressure fr om 131+/-13 to 128+/-12 mm Hg (placebo, 132+/-13 and 132+/-13 mm Hg; P < 0.05 between final examinations) and mean+/-SD 24-hour blood pressu re by -3.3+/-6.9 mm Hg (placebo, +0.7+/-4.6 mm Hg; P < 0.05). Insulin infusion increased LBF significantly in the healthy controls but not i n obese insulin-resistant hypertensive subjects. Obese hypertensive pa tients are resistant to the effects of insulin with regard to both glu cose uptake and vasodilatation. Administration of insulin exerts a sma ll blood pressure-lowering effect in these patients. These data strong ly argue against the postulated presser action of insulin in essential hypertension.