Organic nitrates are polyol esters of nitric acid, whereas organic nitrites are esters of nitrous acid. Nitrate esters (—C—O—NO2) and nitrite esters (—C—O—NO) are characterized by a sequence of carbon—oxygen—nitrogen, whereas nitro compounds possess carbon-nitrogen bonds (C—NO2). Glyceryl trinitrate is not a nitro compound, but the name nitroglycerin is well entrenched. Organic nitrates of low molecular mass (e.g. nitroglycerin) are moderately volatile, oily liquids, whereas the high-molecular-mass nitrate esters (e.g., erythrityl tetranitrate, isosorbide dinitrate, and isosorbide mononitrate) are solids. The organic nitrates and nitrites, collectively termed nitrovasodilators, must be reduced to produce the reactive free radical NO, the active principle of this class of compounds.
Nitrites, organic nitrates, nitroso compounds, and a variety of other nitrogen oxide-containing substances (including nitroprusside) lead to no formation. no activates guanylyl cyclase, increases the cellular level of cyclic GMP, activates PKG, and modulates the activities of PDEs 2, 3, and 5 in a variety of cell types. In smooth muscle, no-mediated increase in intracellular cyclic GMP activate PKG, which leads to reduced phosphorylation of myosin light chain, reduced Ca2+ concentration in the cytosol, and vasorelaxation. Although the soluble isoform of guanylyl cyclase remains the most extensively characterized target for no, no also forms specific adducts with thiol groups in proteins and with reduced glutathione to form nitrosothiol compounds with distinctive biological properties.
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