Renin - Angiotensin - Aldosterone System

Chronic heart failure (CHF) is associated with endothelial dysfunction. Activation of the renin-angiotensin-aldosterone system (RAAS) is believed to be important in the deterioration of endothelial dysfunction in CHF through stimulation of oxidative stress. Whereas angiotensin-converting enzyme inhibitors (ACE-I) improve endothelial function in CHF, the effects of angiotensin II AT 1-receptor blockers (ARB) are less well established. Therefore we compared the effects of the ACE-I lisinopril vs. the ARB candesartan on endothelial dysfunction in a rat model of CHF. CHF was induced by myocardial infarction (MI) after coronary ligation. Two weeks after MI, daily treatment with lisinopril (2 mg/kg) or candesartan cilexetil (1.5 mg/kg) was started. After 13 weeks, rats were sacrificed and endothelial function was determined by measuring acetylcholine (ACh)-induced vasodilation in aortic rings, with selective presence of the nitric oxide synthase (NOS)-inhibitor N G-monomethyl-L-arginine (L-NMMA) to determine the contribution of nitric oxide (NO). ACh-induced vasodilation was attenuated in untreated MI (-50%) compared with control rats. This was in part due to an impaired contribution of NO (-49%). Lisinopril and candesartan cilexetil fully normalised ACh-induced dilation, including the part mediated by NO. Chronic RAAS-blockade with lisinopril and candesartan cilexetil normalised endothelial function in CHF in a comparable way. The effect of both treatments included the increase of the NO-mediated dilation, further indicating the important role of oxidative stress in the relationship between the RAAS and endothelial dysfunction in CHF. Introduction Experimentally, in animal models of chronic heart failure (CHF), 1-3 as well as clinically in heart failure patients, 4,5 endothelial dysfunction has been identified as the impaired dilatory response to acetyl-choline in a setting of preserved responsiveness to vasodilators such as nitroprusside. This endothelial dysfunction, leading to abnormal vasomotor control, may give rise to increased peripheral vascular resistance , a hallmark of CHF. As such, endothelial dys-function is regarded to be one of the underlying and contributing factors for the progressive nature of CHF. 5 Consequently, prevention or reversal of endothelial dysfunction may be considered an important target for pharmacological intervention in CHF.