Group 8 , endogenous nitric oxide

Nitroprusside and organic nitrites (eg, amyl nitrite) and nitrates (eg, isosorbide dinitrate) contain NO groups that can be released as nitric oxide. Arginine is the normal source of endogenous nitric oxide. Histamine stimulates the production of nitric oxide from arginine. The answer is (C). 

The role of CuZnSOD on oxygen radical production in cerebral vessels has been studied. Didion et al. [28] demonstrated that endogenous CuZnSOD diminished superoxide levels in rabbit cerebral blood vessels and affected nitric oxide- and cyclooxygenase-mediated responses in cerebral microcirculation. A subsequent study by the same group [29] showed increased superoxide production and vascular dysfunction in CuZnSOD-deficient mice. Chang et al. [30] suggested that superoxide induced cytokines, which activated microglial... 

As described below, tolerance is an important consideration in the use of nitrates. While tolerance may be caused in part by a decrease in tissue sulfhydryl groups, it can be only partially prevented or reversed with a sulfhydryl-regenerating agent. The site of this cellular tolerance may be in the unknown reaction responsible for the release of nitric oxide from the nitrate, since other agents, eg, acetylcholine, that cause vasodilation via release of nitric oxide from endogenous substrates do not show cross tolerance with the nitrates. 

An additional group of oxygen-containing radicals, termed RNOS, contain nitrogen as well as oxygen. These are derived principally from the free radical nitric oxide (NO), which is produced endogenously by the enzyme nitric oxide synthase. Nitric oxide combines with O2 or superoxide to produce additional RNOS. 

Nitrosothiols are difficult to control as donors, since the release of NO is catalyzed by traces of free metal ions, in particular copper(I) Cu" ". The endogenous synthesis of NO may be enhanced by activating existing nitric oxide synthases with supplementation of cofactors like tetrahydrobiopterin, with folic acid or vitamin C, or by phosphorylation of certain serine groups of the enzyme. Alternatively, the expression of NOS enzyme in tissues or cell cultures may be artificially enhanced by gene therapy, i.e., genetic transfection with viral vectors. Finally, under favorable conditions NO levels may be increased by blocking the... 

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