Identification and measurement of kynurenic acid in the rat brain and other organs

Kynurenic acid, a biologically active tryptophan metabolite, has been identified and measured in the rat brain and other organs using HPLC and GC MS. Both the described methods required extraction of the compound in alkaline ethanol and initial purification on Dowex ion-exchange resins. The GC MS approach used 3-hydroxy-2-naphthoic acid as an internal standard and a derivatization procedure with diazomethane and trifluoroacetic anhydride. The HPLC procedure was performed on a reverse-phase column using a spectrophotometric detector. Both the GC MS and the HPLC methods had the lowest detection limit in the range of 10 pmol/injection, but the variability of the results was lower when HPLC was used. HPLC analysis showed the content of kynurenic acid to be 14 ± 2 pmol/g wet wt in the brain, 75 ± 7 in the heart, 87 ± 8 in the liver, and 298 ± 10 in the kidneys. Comparable but variable values were obtained with GC MS.