Endothelial dysfunction as a primary alteration in vascular diseases

Endothelium controls vascular smooth muscle tone by secreting relaxing and contracting factors. There is a constant release of endothelium derived rel axing factors, mainly nitric oxide, a potent vasodilator, inhibitor of plat elet aggregation, monocyte adhesion and smooth muscle proliferation. In add ition, the endothelium may increase to release of NO in response to humoral stimulation by vasoactive substances such as acetylcholine, bradikinin or substance P. Although the endothelium releases a number of products, no sin gle blood test has yet proved useful to determine normal endothelial functi on or as early abnormalities. The most useful test of endothelial function relies on the measurement of endothelium-dependent dilatation in response t o pharmacological or physiologic stimuli. The alteration of this response i s known as endothelial dysfunction and has been observed in a variety of ci rcumstances related to cardiovascular risk. This review summarizes the evid ence that sustains this association and emphasizes the clinical utility of assessing endothelial function presenting two clinical cases of hypercholes terolemia in which a high-resolution vascular ultrasound in the braquial ar tery was used.