Physiological and pathophysiological roles of nitric oxide

Nitric oxide (NO), identified as the biochemical messenger of endothelial-dependent relaxation, is of obvious chemical simplicity, but the range and complexity of its biological actions are only now emerging. NO is an important determinant of vascular resistance, it reduces thrombogenicity of the vascular endothelium, contributes to non-specific, host-defence mechanisms, and is a neurotransmitter in the peripheral and central nervous systems. In addition to these physiological roles, there is now convincing evidence that excessive, prolonged production of NO contributes to tissue damage in septicemia, ischemia/reperfusion injury, and other inflammatory conditions.