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.