THE L-ARGININE - NITRIC-OXIDE PATHWAY

Nitric oxide (NO) is synthesized from L-arginine by an enzyme called the NO synthase. NO production by vascular endothelial cells accounts for the biological properties of endothelium-derived relaxing factor and maintains a vasodilator tone. Platelets also produce NO, which modulates their aggregability. In the central nervous system NO mediates the effects of excitatory amino acids. In all these tissues the L-arginine: NO pathway acts as a transduction mechanism for the soluble guanylate cyclase, for which NO is the endogenous stimulator. NO is also released after immunological stimulation in macrophages, neutrophils, and other cells. NO thus released acts as part of the host defense mechanism, for it is cytotoxic or cytostatic for tumor cells and invasive organisms and may mediate other aspects of the immunological response. Discovery of the L-arginine: NO pathway has far reaching implications for the understanding of several areas in biology and indicates potential novel therapies for a number of diseases.