Synthesis and Metabolism of Quinolinic Acid Ring Labeled with Tritium.

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Abstract
Quinolinic acid was labeled in the 4, 5, and 6 positions with tritium by the neutron recoil method. Intraperitoneal injection of the labeled quinolinic acid into rats was followed by excretion of labeled N1-methylnicotinamide in the urine during the next 24 hours. Tritium contents of the excreted N1-methylnicotinamide in two experiments indicated that 7.6 and 23.6% originated from the injected labeled quinolinic acid. Evidence is definite that quinolinic acid can serve in the rat as a source of niacin. Most of the injected quinolinic acid was excreted as such in the urine. The quinolinic acid isolated from the urines of 2 rats had specific activities of 103 and 112% of the injected quinolinic acid. The increase in specific activity suggests that the tritium-labeled quinolinic acid may have been less rapidly metabolized than the unlabeled substance.