AT 1 -Receptor Antagonism Improves Endothelial Function in Coronary Artery Disease by a Bradykinin/B 2 -Receptor-Dependent Mechanism

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Abstract
Impaired flow-dependent, endothelium-mediated vasodilation is an early finding in patients with coronary artery disease (CAD). Experimental and some clinical studies observed that angiotensin type-1 receptor antagonists (AT1A) enhance endothelium-dependent relaxation in CAD. The present study was designed to determine whether AT1A improves flow-dependent dilation (FDD) in patients with CAD and, if so, whether bradykinin and NO are involved. High-resolution ultrasound was used to measure radial artery diameter at rest and during reactive hyperemia, causing endothelium-mediated vasodilation. Twenty patients with CAD were randomly assigned to receive intrabrachial infusion of candesartan (800 microg/min) with and without icatibant, a bradykinin B2-receptor antagonist (90 microg/min; group A) or N-monomethyl-l-arginine (L-NMMA), an NO-synthase inhibitor (7 micromol/min; group B). The AT1A candesartan improved FDD by >40%, an effect that was inhibited by icatibant (group A: control, 7.3+/-0.9; candesartan, 10.3+/-1.1; candesartan+icatibant, 5.0+/-0.5%). Similarly, L-NMMA blunted the beneficial effect of candesartan (group B: control, 6.3+/-0.6; candesartan, 8.9+/-0.6; candesartan+L-NMMA: 4.7+/-0.5%; each P<0.01). The angiotensin type-1 receptor antagonist candesartan improves flow-dependent, endothelium-mediated vasodilation in patients with CAD. This effect is inhibited by either icatibant and or L-NMMA, suggesting that both bradykinin and NO contribute to the vascular effects of AT1-receptor antagonists in this patient population.