Metabolism of 1,3,7-trimethyldihydrouric acid in the rat: new metabolic pathway of caffeine.

[1-CH3-14C] 1,3,7-trimethyldihydrouric acid which, in quantity, is the most important caffeine metabolite, was isolated and purified from the urine of rats fed with [1-CH3-14C] caffeine. The oral administration of this metabolite to rats showed that 1,3,7-trimethyldihydrouric acid was excreted unchanged in urine and was therefore an end product of caffeine metabolism. This result implies a new metabolic pathway of caffeine.