Nitric oxide, NO, which is generated by various components of the immune system, has been presumed to be cytotoxic. However, NO has been proposed to be protective against cellular damage resulting during ischemia reperfusion. Along with NO there is often concomitant formation of superoxide/hydrogen peroxide, and hence a synergistic relationship between the cytotoxic effects of nitric oxide and these active oxygen species is frequently assumed. To study more peroxide or to hypoxanthine/xanthine oxidase resulted in the degradation of the dopamine uptake and release mechanism. As was observed in the case of the V79 cells, the presence of NO essentially abrogated this peroxide-mediated cytotoxic effect on mesencephalic cells.Nitric oxide, NO, is one of the proposed cytotoxic species produced by the immune surveillance system (1, 2). Many reports also suggest that during the ischemia reperfusion event, NO mediates tissue injury (3)(4)(5)(6)(7)(8)(9)(10)(11)(12). However, it has been suggested that NO can function as a protective agent on the basis of two lines of evidence: (i) NO synthase (NOS) inhibitors increase tissue damage during in vivo ischemia reperfusion within the cerebral cortex, and (ii) in more direct evidence, NO has been shown to prevent damage during ischemia reperfusion events in both brain and heart (13-18). Additional studies provide evidence that NO, though present, plays a minimal role in the pathological effects associated with ischemia reperfusion injury (19,20) or tumor necrosing factor-mediated cytotoxicity (21). Unfortunately, the exact role(s) NO plays in cytotoxicity in vivo is not clear because there are a number of different physiological functions NO or the NOS inhibitors could affect simultaneously. It has been proposed that NO or reactive nitrogen oxide species can directly cause cell death. However, primary neuronal cell cultures exposed to concentrations of NO as high as 1 mM show no adverse effects (22, 23). Many of the biological events in which NO has been proposed as a toxin occur concurrently with the production of reactive oxygen species-e.g., immune response and ischemia reperfusion injury.To clarify the relationship between the cytotoxic properties of the reactive oxygen species and NO, it is necessary to simplify the system. We now show that NO released from a series of compounds known as the "NONOates" (24) Abstract Service Registry Number 136587-13-8) were synthesized and assayed for NO production via chemiluminescence technique as described (24).Enzyme Analysis/Controls. The activity of XO was monitored in the absence and presence of 1 mM DEA/NO by two different assays. (i) Superoxide-induced reduction of ferricytochrome c to ferrocytochrome c was monitored spectrophotometrically at 550 nm (25). The reaction was carried out in a 1-ml volume in aerated 50 mM phosphate buffer (pH 7.8) containing 50 ,AM diethylenetriaminepentaacetic acid. HX was maintained at 2.5 mM and ferricytochrome c at 20 ,uM. The reactions were initiated with the addition of XO (final con...

The critical regulatory function of nitric oxide (NO) in many physiologic processes is well established. However, in an aerobic aqueous environment NO is known to generate one or more reactive and potentially toxic nitrogen oxide (NOx) metabolites. This has led to the speculation that mechanisms must exist in vivo by which these reactive intermediates are detoxified, although the nature of these mechanisms has yet to be elucidated. This report demonstrates that among the primary bioorganic products of the reaction of cellular constituents with the intermediates of the NO/O2 reaction are S-nitrosothiol (S-NO) adducts. Anaerobic solutions of NO are not capable of nitrosating cysteine or glutathione, while S-NO adducts of these amino acids are readily formed in the presence of O2 and NO. Investigation of the kinetics for the formation of these S-NO adducts has revealed a rate equation of d[RSNO]/dt = kSNO[NO]2[O2], where kSNO = (6 +/- 2) x 10(6) M-2S-1, a value identical to that for the formation of reactive intermediates in the autoxidation of NO. Competition studies performed with a variety of amino acids, glutathione, and azide have shown that cysteine residues have an affinity for the NOx species that is 3 orders of magnitude greater than that of the nonsulfhydryl amino acids, and > 10(6) times greater than that of the exocyclic amino groups of DNA bases. The dipeptide alanyltyrosine reacts with the intermediates of the NO/O2 reaction with an affinity 150 times less than that of the sulfhydryl-containing compounds. Furthermore, Chinese hamster V79 lung fibroblasts depleted of glutathione display enhanced cytotoxicity on exposure to NO.(ABSTRACT TRUNCATED AT 250 WORDS)

In rat striatal membranes, NaCl induced a twofold increase in the maximal number of cocaine binding sites but did not alter the affinity of these sites for cocaine. This effect was concentration-dependent, specific to sodium ions, and occurred in membranes prepared from corpus striatum but not from other brain regions. Lesions with 6-hydroxydopamine but not with kainic acid eliminated the sodium-induced increase in binding and produced a decrease in the Bmax of binding measured in the presence of NaCl. The capacity of a series of drugs to interfere with Na+-dependent cocaine binding correlated well with their capacity to inhibit [3H]dopamine uptake into rat striatal synaptosomes. The present results suggest that Na+-dependent cocaine binding sites are localized presynaptically on dopaminergic nerve terminals in corpus striatum, and may be related to dopamine uptake sites.

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