Glutamate induces hydroxyl radical formation in vivo via activation of nitric oxide synthase in Sprague–Dawley rats

Abstract

It was recently reported that neuronal nitric oxide synthase (NOS) generates oxygen-derived free radicals in vitro at low concentrations of l-arginine. Using the microdialysis technique, we monitored both hydroxyl radical ( ⋅OH) and nitric oxide ( ⋅NO) formation in rat striatum perfused with glutamate (500 mM). ⋅OH and ⋅NO were quantitated in microdialysates by measuring the amounts of the non-enzymatic hydroxylation product of salicylate (2,3-dihydroxybenzoic acid) and the metabolites of ⋅NO (nitrite+nitrate), respectively. ⋅OH levels were dramatically increased during glutamate perfusion, while ⋅NO generation was virtually abolished. ⋅OH production was inhibited by the specific NOS blocker, N G-nitro- l-arginine methyl ester. This effect was not reversed but potentiated by l-arginine. Thus, it is likely that NOS generates oxygen-derived free radicals instead of ⋅NO in brain subjected to highly excitotoxic conditions.