A fluorimetric assay for the determination of anthranilic acid in biological materials

In the brain, anthranilic acid may serve as a bioprecursor of the endogenous excitotoxin quinolinic acid. Using a novel isolation procedure followed by HPLC and fluorimetric detection, we have developed an assay which is sufficiently sensitive to determine anthranilic acid in small (> or = 3 mg) samples of rat brain tissue (sensitivity limit: 50 fmol). Anthranilic acid was identified by its retention time in three chromatographic systems. The assay was applied to the measurement of anthranilic acid in rat serum (131 +/- 7 nM) and urine (9.9 +/- 118 nmol/mg creatinine) and in several organs which contained between 0.5 and 2 pmol anthranilic acid/mg protein. Only small differences in anthranilic acid content were found among 10 regions of the rat brain. Neuronal depletion induced by an intrastriatal excitotoxin injection resulted in an increase in anthranilic acid levels, suggesting a nonneuronal localization of the metabolite in the brain. This assay should provide an improved means for the investigation of the neurobiology of anthranilic acid.