| [ Summary ] |
Nitric oxide (NO) is synthesized from L-arginine by an enzyme, called NO synthase (NOS). Two types of NOS have been identified ; one is a constitutive NOS (cNOS), that is expressed under normal conditions, and the other referred to as inducible NOS (iNOS), is induced by inflammatory cytokines. The NO produced by CNOS acts as a transduction molecule underlying various physiological responses, whereas that produced by iNOS acts as a cytotoxic molecule to kill the invade microorganism or tumor cells. The dual actions of NO are also seen in the stomach : cNOS/NO plays a role in maintaining mucosal integrity, in collaboration with other protective factors such as prostaglandins(PGs) and sensory neurons. However, iNOS/NO exerts complex influences, playing the part of both a pathogenic and a protective molecule, depending on the particular experimental conditions. Further studies should be done to disclose the interactive role of NO in relation to other protective factors, such as PGs, as well as the nature of the dual reactions induced by NO in the gastric mucosa. |