In mammals, NO which is the smallest signalling molecule known, can be generated by three different isoforms of the enzyme NO synthase, i.e. neuronal ‘n’NOS (or NOS I), inducible ‘i’NOS (or NOS II), and endothelial ‘e’NOS (or NOS III). They all utilize l-arginine and molecular oxygen as substrates and require the cofactors reduced nicotinamide-adenine-dinucleotide phosphate (NADPH), flavin adenine dinucleotide (FAD), flavin mononucleotide (FMN), and (6R-)5,6,7,8-tetrahydrobiopterin (BH4). All three NOS isozymes have regulatory functions in the cardiovascular system. Neuronal NOS is involved in central regulation of blood pressure, and nNOS-containing (nitrergic) nerves can dilate certain vascular beds[1].