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Angiotensin II type 1 receptor blockade: a novel therapeutic concept
1Department of Medicine, University of Melbourne, Austin and Repatriation Medical Centre, Victoria, Australia.
Abstract:
Angiotensin II type 1 (AT1) receptor blockers, such as candesartan, are attractive alternatives to ACE inhibitors in the treatment of hypertension and cardiovascular disease. Although angiotensin-converting enzyme (ACE) inhibitors are able to suppress the renin-angiotensin system (RAS), their mechanism of action may limit their clinical utility in the treatment of hypertension. For example, they act as competitive inhibitors of ACE. This means that their effects can be overcome by high levels of angiotensin I, which occur after ACE inhibition due to removal of the negative feedback effect of angiotensin II on renal renin release. ACE inhibitors are also unable to block the production of angiotensin II by non-ACE-mediated pathways. Furthermore, ACE is not a specific enzyme. Its inhibition therefore has effects on other substances, such as bradykinin, leading to the class-specific side effects associated with ACE inhibitors. Candesartan, on the other hand, binds insurmountably to the AT1-receptor, thereby providing more complete blockade of the negative cardiovascular effects of angiotensin II than is possible with ACE inhibitors. The specificity of AT1-receptor blockade also ensures that efficacy is achieved without inducing the side effect of cough that results from the non-specific consequences of ACE inhibition. Preclinical and early clinical studies demonstrate that AT1-receptor blockers produce at least the same degree of target-organ protection as has been demonstrated for ACE inhibitors. Additional benefits of AT1-receptor blockers may arise from the fact that, unlike ACE inhibitors, they do not prevent the activity of angiotensin II on AT2-receptors in the heart, which is thought to reduce cardiac remodelling. From a mechanistic perspective, therefore, AT1-receptor blockers appear to have advantages over ACE inhibitors, in terms of a more complete blockade of angiotensin II effects, while also avoiding the specific side effects associated with ACE inhibition.