Plasma endothelin concentrations are elevated in cirrhosis and correlate with disease severity. This study assessed forearm vascular responses to exogenous endothelin-1 (ET-1), and evaluated the contribution of endogenous ET-1 to the maintenance of basal peripheral vascular tone in patients with well-compensated cirrhosis (n ؍ 11) and matched healthy controls (n ؍ 8). Bilateral forearm blood flow (FBF) was measured at baseline and following unilateral, subsystemic, intrabrachial artery infusions of ET-1 (2 and 6 pmol/min); BQ-123, a selective ET A receptor antagonist (3 and 10 nmol/min); and BQ-788, a selective ET B receptor antagonist (0.3 and 1 nmol/min) using venous occlusion plethysmography. Baseline systemic hemodynamics and plasma ET-1 and big ET-1 concentrations were measured using electrical bioimpedance and radioimmunoassay, respectively. Patients and controls had similar baseline FBF, systemic hemodynamics, and plasma ET-1 and big ET-1 concentrations. In both groups, ET-1 and BQ-788 caused significant vasoconstriction (P < .001) and BQ-123 caused significant vasodilatation (P < .001). Compared with controls, cirrhotic patients had attenuated ET-1 responses (P < A hyperdynamic circulation characterized by low arterial pressure, high cardiac output, and low systemic vascular resistance is a feature of patients with advanced cirrhosis and portal hypertension. [1][2][3] This hyperdynamic circulation worsens with disease progression [4][5][6] and is accompanied by a reduced reactivity to vasopressor systems including the reninangiotensin and sympathetic nervous systems. These hemodynamic changes play a crucial role in the pathogenesis of portal hypertension and its complications, including variceal hemorrhage, ascites, and the hepatorenal syndrome. 7,8 Endothelin-1 (ET-1) is the most potent vasoconstrictor known, belonging to a 21-amino acid peptide family with a range of biological effects. 9-11 ET-1 was originally identified in the culture medium of porcine aortic endothelial cells 9,10 and is derived from a larger pre-pro-endothelin-1 (212 amino acids), which is cleaved by endopeptidases to produce big ET-1 (38 amino acids), which is then converted to ET-1 by specific endothelin-converting enzymes. [9][10] Molecular studies have, so far, identified 2 endothelin receptor subtypes in mammalian species: endothelin-A (ET A ) and endothelin-B (ET B ). In vascular smooth muscle cells, both receptors are expressed 11,12 and mediate vasoconstriction. [11][12][13][14] Only the ET B receptors are found on endothelial cells, where these cause vasodilatation through the release of endothelium-derived vasodilators, such as nitric oxide (NO). 15 ET-1-induced vasoconstriction is predominantly mediated by the ET A receptor, but ET B receptors may contribute under some circumstances. 16 Since 1991, many studies have reported increased plasma concentrations of ET-1 in patients with cirrhosis. [17][18][19][20][21][22][23][24][25][26] The mechanisms underlying the elevated ET-1 concentrations are unclear and do not appe...