A novel spectrophotometric nitrite (NO-2) nitrate (NO-3) assay system for a small quantity (5 μl) of dialysate sample obtained by in vivo brain microdialysis was developed based on the diazotization reaction. The system has the advantages of in vivo consecutive measurement, high precision, good reproducibility, technical simplicity, relatively short resolution time (2.5-20 min), and wide availability. The NO-3 level in the rat striatum was found to be 3 times higher than the NO-2 level. A nitric oxide (NO) synthase inhibitor, NG-nitro-l-arginine methyl ester, reduced striatal NO-2 citrulline formation in a dose-related manner and increased arginine, indicating that the tissue NO-2 level detected by this assay system adequately reflects the striatal NO synthase activity.
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