Metabolism of Thiamine and Thiamine Tetrahydrofurfuryl Disulfide to 4-Methylthiazole-5-Acetic Acid in Conventional and Germfree Rats under Various Dosing Conditions

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Abstract
The urinary excretion of thiamine and 4-methylthiazole-5-acetic acid was studied in both conventional and germfree rats under various dosing conditions of thiazole-2-14C-labeled thiamine or thiamine tetrahydrofurfuryl disulfide. The urine was fractionated by Amberlite CG-50 chromatography and the thiazole acid was determined by the isotope dilution method. Thiamine, in an oral dose larger than 1.5 mg/rat, was predominantly excreted in the urine after conversion to the thiazole acid, whereas most of the injected thiamine was eliminated unchanged. The thiamine moiety of thiamine tetrahydrofurfuryl disulfide was also converted to the thiazole acid upon oral ingestion but less was excreted as the thiazole acid and more as the unchanged thiamine, comparing with the administration of thiamine. Time course study on the urinary metabolite pattern showed that most of the thiazole acid was excreted during the first 3 hours after oral ingestion of both vitamins. The thiazole acid was also identified as a metabolite of thiamine in germfree rats and there was no essential difference in the urinary metabolite pattern between conventional rats and germfree ones. This finding indicates that intestinal microflora are not primarily responsible for the conversion of thiamine to the thiazole acid in the rat.