Nitric oxide (NO) was once regarded as a noxious environmental pollutant, when in the 1980s several lines of research showed that NO is essential of the human body. NO is a short-lived gas that is produced locally from L-arginine by the enzyme NO-synthase NOS). NOS is found in preganglionic and postganglionic autonomic neurons, as well as in vascular endothelial cells. Inside the VSMC (vascula…