Improved endothelium-dependent vasodilation after blockade of endothelin receptors in patients with essential hypertension

Abstract

Background - Hypertensive patients have both impaired endothelium-dependent vasodilation and increased activity of the endothelin (ET-1) system, which participate in their increased vascular tone and may predispose them to atherosclerosis. This study investigated the contribution of increased ET-1 activity to the impaired endothelium-dependent vasodilator function of hypertensive patients. Methods and Results - Forearm blood flow (FBF) responses to intraarterial infusion of acetylcholine (ACh; 7.5, 15, and 30 μg/min) and sodium nitroprusside (SNP; 0.8,1.6, and 3.2 μg/min) were assessed by strain-gauge plethysmography before and after nonselective blockade of ETA and ETB receptors by combined infusion of BQ-123 (ETA blocker; 100 nmol/min) and BQ-788 (ETB blocker; 50 nmol/min). During saline administration, the vasodilator response to ACh was significantly blunted in hypertensive patients compared with controls (P<0.001), whereas the vasodilator effect of SNP was not different between groups (P=0.74). Blockade of ET-1 receptors resulted in a significant increase in FBF from baseline in hypertensive patients (P<0.008) but not in controls (P=0.15). In hypertensive patients, a combined ETA/B blockade resulted in a significant potentiation of the vasodilator response to ACh compared with saline (P=0.01), whereas the response to SNP was unchanged (P=0.44). In contrast, the response to ACh was not significantly modified by ET-1 receptor antagonism in healthy subjects (P=0.14 compared with saline). Conclusions - These findings indicate that blockade of ET-1 receptors improves endothelium-dependent vasodilator function in hypertensive patients, thereby suggesting that an increased ET-1 activity may play a role in the pathophysiology of this abnormality.