In the failing heart, the local angiotensin II concentration is increased, and the extent of cardiac angiotensin II release is related to the clinical signs of heart failure. The enzymes involved in myocardial generation of angiotensin II are the angiotensin-converting enzyme (ACE) and chymases. While myocardial angiotensin II is mainly generated by chymases in the human heart, ACE inhibitors nevertheless improve left ventricular (LV) function, attenuate LV remodelling and reduce mortality in heart failure patients. These beneficial actions of ACE inhibitors, however, relate to their beneficial effect on kinin metabolism. Angiotensin II type 1 receptor (AT1) antagonists also mediate part of their beneficial effects through increased bradykinin formation. However, in contrast to ACE inhibitors, AT1 receptor antagonists attenuate downstream signalling of angiotensin II-induced AT1 receptor activation, which increases the activity of existing proteins (e.g. NADPH oxidase) and the de novo synthesis of proteins (e.g. inducible nitric oxide synthase, tumor necrosis factor-alpha ) in cardiomyocytes. Given the multiple actions of AT1 receptor activation on cardiomyocyte and non-cardiomyocyte function in the presence of an increased myocardial AngII concentration, the reduction of cardiovascular mortality and rate of hospitalization following AT1 receptor blockade in heart failure patients not receiving ACE inhibitors is not surprising. Most importantly, the beneficial effects of AT1 receptor blockade are not only achieved when used as an alternative to ACE inhibition, but also when used on top of ACE inhibitors.
Copyright 2005 S. Karger AG, Basel.