Metabolism of Thiamine-S35 in the Rabbit.

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Abstract
The fat of thiamine (vitamin B1), labeled with sulfur-35 in the thiazole moiety, was studied in rabbits after oral and parenteral administration of doses in the physiological range (50-200 [mu]g). Urinary and fecal sulfur fractions, inorganic sulfate (IS), ethereal sulfate (ES), and neutral sulfur (NS), were isolated and analyzed for S35 content by conversion of all sulfur to barium sulfate, and measurement of radioactivity in a windowless flow-gas Geiger-Mueller counter. In 4 to six 24-hour periods following administration of thiamine-s35 (B1-S35), average total recoveries of S35 were: 77% after administration by stomach tube, 86% after intramuscular injection, and 54% after intravenous injection. When the oral dose of B1-S35 was followed 6 hours later by an intramuscular injection of a 20-fold larger dose of non-radioactive thiamine, an additional 17% of the S35 was recovered in the urine, indicating a flushing out of the B1-S35 by the excess of injected non-radioactive B1. In all cases, the NS fraction of urine contained more than 50% of the recovered S35, and the greater portion of this was excreted in the first 24-hour period; urinary IS and ES, and the fecal sulfur fractions, are minor excretory pathways for B1-S35 and its metabolites. The main metabolites, unchanged B1-S35 and its thiazole-s35 moiety, were isolated from the urine after oral administration of B1-S35, the former by adsorption on a strong cation exchange resin, and the latter by ether extraction. The unchanged B1-S35 and thiazole-S35 moiety together accounted for approximately 95% of the S35 of the NS fraction in the first 24-hour period, and were excreted in a ratio of 2:1, respectively.

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