Impaired Endothelium-Dependent Vasodilation in Patients With Essential Hypertension

Abstract

Background Patients with essential hypertension have abnormal endothelium-dependent vascular relaxation, largely related to reduced bioactivity of nitric oxide (NO). The purpose of the present investigation was to determine whether this defect is due to a deficit at the specific intracellular signal-transduction pathway level or is a consequence of a more generalized endothelial abnormality. Methods and Results The responses of the forearm vasculature to acetylcholine and bradykinin (endothelium-dependent agents that act through different signal transduction pathways) and to sodium nitroprusside (a direct dilator of vascular smooth muscle) were studied in 10 hypertensive patients (5 men, 5 women; aged 48±9 years old [mean±SD]) and 12 control subjects (6 men, 6 women; aged 48±7 years old). To determine the contribution of NO to bradykinin-induced vasodilation, the vascular responses to bradykinin were also measured after administration of N G -monomethyl- l -arginine, an arginine analogue that inhibits the synthesis of NO. Drugs were infused into the brachial artery, and forearm blood flow was measured by strain-gauge plethysmography. The response to acetylcholine was significantly blunted in hypertensive patients (maximal blood flow, 7.5±2 versus 16.6±8 mL · min −1 · 100 mL −1 in control subjects [mean±SD]; P <.005). Similarly, the vasodilator effect of bradykinin was significantly reduced in hypertensive patients compared with control subjects (maximal blood flow, 8.7±2 versus 15.8±6 mL · min −1 · 100 mL −1 in control subjects; P <.005). A significant correlation was found between the maximal blood flow with acetylcholine and that with bradykinin ( r =.89). No significant differences were found between the two groups for vascular response to sodium nitroprusside. N G -monomethyl- l -arginine significantly blunted the response to bradykinin in control subjects (maximal blood flow decreased from 15.8±6 to 10.1±2 mL · min −1 · 100 mL −1 , P <.003). In contrast, inhibition of NO synthesis did not modify the response to bradykinin in hypertensive patients (maximal blood flow, 8.7±2 and 8.5±3 before and during infusion of N G -monomethyl- l -arginine, respectively; P =NS). As a consequence, the response to bradykinin after inhibition of NO synthesis was not significantly different between the two groups. Conclusions Patients with essential hypertension have impaired endothelium-dependent vasodilator responses to both acetylcholine and bradykinin. These findings indicate that the endothelial dysfunction in this condition is not related to a specific defect of a single intracellular signal-transduction pathway and suggest a more generalized abnormality of endothelial vasodilator function.