Insulin Resistance and the Effect of Insulin on Blood Pressure in Essential Hypertension

Abstract

Abstract —The aim of this study was to investigate the effect of 2 weeks of insulin administration on blood pressure and to simultaneously measure insulin sensitivity and insulin-induced vasodilatation in obese hypertensive patients. In a prospective, randomized, double-blind, crossover study (study 1), 23 obese, untreated, nondiabetic, hypertensive patients received either neutral protamine Hagedorn (NPH) insulin (0.3 U/kg body wt per day) or placebo subcutaneously for 2 weeks (washout period, 2 weeks). Office and 24-hour blood pressure values were measured at the beginning and end of each treatment period. In an open-label study (study 2), 8 obese hypertensive patients and 10 healthy control subjects 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 plethysmography. Insulin administration decreased mean±SD office blood pressure from 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 pressure 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 in obese insulin-resistant hypertensive subjects. Obese hypertensive patients are resistant to the effects of insulin with regard to both glucose uptake and vasodilatation. Administration of insulin exerts a small blood pressure–lowering effect in these patients. These data strongly argue against the postulated pressor action of insulin in essential hypertension.