| [ Summary ] |
Nitric oxide (NO) is a diffusible and reactive molecule, which plays important roles in the vascular, nervous, gastro-intestinal and immune systems. NO is synthesized from L Arginine by a family of three NO synthases(NOS). NOSs are characterized as cytochrome P-450-like hemeproteins, which have a reductase domain at the C terminus and an oxidative domain at the N terminus. Neuronal NOS(nNOS, NOS1) and endothelial NOS(eNOS, NOS3) are constitutive and termed cNOS.CNOS is dormant until activated briefly by Ca2+ transients. NO produced by nNOS in the brain acts as neuromodulator to control behavioral activity,influence memory formation,and intensify responses to painful stimuli. In the peripheral nervous systems, NO regulates gastrointestinal motility, regional blood flow and neuroendocrine function. NO from eNOS in the vascular endothelium causes vasorelaxation and is a principal factor involved in the antiatherosclerotic propertis of the endothelium. A third NOS (iNOS, NOS2) is expressed only after transcriptional induction, but once induced by endotoxins or cytokines, iNOS is active for prolonged periods and produces large amount of NO, which plays important roles in sepsis and inflammation. |