The role of nitric oxide on endothelial function.

The vascular endothelium is a monolayer of cells between the vessel lumen and the vascular smooth muscle cells. Nitric oxide (NO) is a soluble gas continuously synthesized from the amino acid L-arginine in endothelial cells by the constitutive calcium-calmodulin-dependent enzyme nitric oxide synthase (NOS). This substance has a wide range of biological properties that maintain vascular homeostasis, including modulation of vascular dilator tone, regulation of local cell growth, and protection of the vessel from injurious consequences of platelets and cells circulating in blood, playing in this way a crucial role in the normal endothelial function. A growing list of conditions, including those commonly associated as risk factors for atherosclerosis such as hypertension, hypercholesterolemia, smoking, diabetes mellitus and heart failure are associated with diminished release of nitric oxide into the arterial wall either because of impaired synthesis or excessive oxidative degradation. The decreased production of NO in these pathological states causes serious problems in endothelial equilibrium and that is the reason why numerous therapies have been investigated to assess the possibility of reversing endothelial dysfunction by enhancing the release of nitric oxide from the endothelium. In the present review we will discuss the important role of nitric oxide in physiological endothelium and we will pinpoint the significance of this molecule in pathological states altering the endothelial function.