摘要：Nitric oxide (NO · ) synthesized in endothelial cells , from the terminal guanidino nitrogen atom of L-ARG, by means of NO-synthase (NOS), activates guanylyl-cyclase in smooth muscle cells and plateletes , increasing the levels of the intracellular messenger cyclic guanylyl phosphate ( GMPc ). This phenomens produces smooth muscle relaxation and platelet aggregation inhibition , presumably by reduction of the intracellular free Ca2+ concentration . The endothelial vasodilator prostacyclin causes the same effects through adenylyl-cyclase activation , which increases intracellular level of AMPc . The biological activity of NO · may be modified by oxygen-derived reactive species , such as anion superoxide (O2), hydrogen peroxide (H2O2) and hydroxyl radical (OH · ), contributing to regulate the vascular tone. NO · may posses both cytoprotective and cytotoxic properties , depending on the amount and the isoform of NOS. NO · may regulate hepatic metabolism directly by causing alterations in hepatocellular metabolism and function , or indirectly as a result of its vasodilator properties .
关键词： nitric oxide (NO · ), oxygen-derived reactive species , peroxynitrite (ONOO¯), cytoprotective or/ and cytotoxic properties
