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The endothelium and the renin-angiotensin system.

An enhanced risk for myocardial infarction has been observed in humans with sustained activation of the local and/or systemic renin-angiotensin system, such as a high renin-sodium profile or a heritably enhanced expression of angiotensin converting enzyme. Chronic renin-angiotensin system blockade by angiotensin converting enzyme inhibition reduces the rate of myocardial reinfarction in patients with moderate heart failure. Preliminary experimental evidence suggests that these clinical observations may be partially explained by a proatherogenic effect of an activated renin-angiotensin system, which can downregulate the expression of the endothelial nitric oxide synthase III. Nitric oxide exerts many potentially antiatherogenic effects on endothelium, platelets and low density lipoproteins and indirectly on monocytes and leukocytes Hypertension-induced chronic distension of elastic arteries upregulates the local renin-angiotensin system in these arteries and thereby downregulates nitric oxide synthase. Enhanced local synthesis of the trophic factor angiotensin-II and reduced releasability of the antitrophic factor nitric oxide appear to cooperate in the trophic adaptation of the distended vessel wall to the enhanced load, but with the disadvantage of enhanced susceptibility for atheroma development due to reduced availability of nitric oxide. Chronic blockade of the renin-angiotensin system by angiotensin converting enzyme inhibitors or by angiotensin receptor type-1 antagonists normalizes a reduced endothelial nitric oxide availability in several models, partially by a bradykinin-dependent mechanism. This endothelial protection proved to attenuate the progression of atherosclerosis in experimental models. The antiatherogenic potential of renin-angiotensin system blockade in humans is presently under study.