NITRIC-OXIDE PRODUCTION AND PERIVASCULAR TYROSINE NITRATION IN BRAIN AFTER CARBON-MONOXIDE POISONING IN THE RAT

Nitric oxide is a short-lived free radical and physiological mediator which has the potential to cause cytotoxicity, Studies were conducted to investigate whether nitric oxide, and the potent oxidant peroxynitr ite, were generated in brain during experimental carbon monoxide (GO) poisoning in the rat, Nitric oxide production was documented by electr on paramagnetic resonance spectroscopy, and found to be increased by n inefold immediately after CO poisoning. Evidence that peroxynitrite wa s generated was sought by looking for nitrotyrosine in the brains of G O-poisoned rats. Nitrotyrosine was found deposited in vascular walls, and also diffusely throughout the parenchyma in immunocytochemical stu dies. The affinity and specificity of an anti-nitrotyrosine antibody w as investigated and a solid phase immunoradiochemical assay was develo ped to quantify nitrotyrosine in brain homogenates, A 10-fold increase in nitrotyrosine was found in the brains of GO-poisoned rats. Platele ts were involved with production of nitrotyrosine in the early phase o f exposure to CO, However, nitrotyrosine formation and leukocyte seque stration were nor decreased in thrombocytopenic rats poisoned with 60 according to the standard model. When rats were pre-treated with the n itric oxide synthase inhibitor, L-nitroarginine methyl ester, formatio n of both nitric oxide and nitrotyrosine in response to CO poisoning w ere abolished, as well as leukocyte sequestration in the microvasculat ure, endothelial xanthine dehydrogenase conversion to xanthine oxidase , and brain lipid peroxidation. We conclude that perivascular reaction s mediated by peroxynitrite are important in the cascade of events whi ch lead to brain oxidative stress in CO poisoning.