Excretion of Metabolites of 14C-Pyrimidine-labeled Thiamine by the Rat at Different Levels of Thiamine Intake

Abstract

The effect of the level of intake of radioactive thiamine on the quantitative and qualitative aspects of the urinary excretion of thiamine metabolites was studied in rats. Rats were maintained with different levels of ¹⁴C-pyrimidine-labeled thiamine (8, 20, 30, 50, 100 µg/day) and urinary metabolites were partitioned by column and paper chromatography. Five peaks of radioactivity were obtained. The percentage of total radioactivity in three of these peaks remained constant at all intake levels. The percentage of radioactivity declined in one peak and increased in another as intake increased. Virtually no thiamine appeared in the urine at intake levels of less than 100 µg/day or at tissue levels of less than 75% of saturation. At the lower levels of intake, the thiamine content of the urine as assayed microbiologically was only about 2% of that predicted from the radioactivity. About 13% of the radioactivity of the intake appeared daily in the feces. The thiamine values found for tissues by microbiological assay were somewhat higher than those obtained by radioactivity measurement. The microbiologically inactive products of thiamine metabolism observed in the urine are apparently not present in appreciable quantity in the tissues.