Effect of angiotensin II type 1 receptor antagonism on endothelial function: role of bradykinin and nitric oxide.

BACKGROUND: The important role of the endothelium for regulation of vascular tone, growth, inflammatory response, coagulation and thrombocyte adhesion has now been recognized. Endothelial function has largely been assessed as endothelium-dependent vasodilation, assuming that endothelium-dependent vasomotion represents a surrogate marker for other important endothelial functions. An important rational for this approach has been the observation that both endothelium-dependent vasomotion and other protective endothelial functions are at least partially mediated by nitric oxide. Accumulating clinical studies have now demonstrated a close and independent association of impaired endothelium-dependent vasodilation with cardiovascular events and prognosis. These findings have stimulated interest in treatment options to improve endothelial function in patients at high cardiovascular risk. DISCUSSION: This article describes recent insights into endothelial effects of both angiotensin-converting enzyme (ACE) inhibition and angiotensin II type 1 (AT1) receptor blockade, which have both been shown to improve endothelial function (i.e. by increasing endothelial nitric oxide availability via bradykinin-dependent endothelial nitric oxide release). ACE has a high affinity for bradykinin and degrades the peptide, so ACE inhibition may increase bradykinin-dependent effects by preventing bradykinin degradation. Interestingly, AT1-receptor blockade appears to stimulate the bradykinin-nitric oxide pathway by increased angiotensin II type 2 receptor activation. Moreover, both treatment strategies prevent increased inactivation of endothelial nitric oxide by oxygen radicals, by reducing AT1-receptor-dependent activation of the oxidant enzyme NADPH oxidase and increasing the activity of the vascular antioxidant enzyme extracellular superoxide dismutase. These beneficial effects of ACE inhibition and AT1-receptor blockade are likely to contribute to their effects on cardiovascular events.