Catabolism of 14C-Thiazole-labeled Oxythiamine and Its Effects on Thiamine Catabolism in the Rat

Abstract

The metabolism of oxythiamine and its effects on thiamine metabolism were studied. Three groups of six rats each were injected daily with 40 µg ¹⁴C-thiamine, 40 µg ¹⁴C-thiamine + 80 µg oxythiamine, or 40 µg thiamine + 80 µg ¹⁴C-oxythiamine. Injections were continued for 8 to 20 weeks after which time the urinary excretions of thiamine and oxythiamine metabolites were studied. Under these conditions oxythiamine was less susceptible to destruction by opening of the thiazole ring than was thiamine. Oxythiamine was poorly retained by the rat tissue but enhanced the excretion of thiamine. Injection of somewhat higher oxythiamine-to-thiamine ratios (4:1, 6:1) resulted in a decrease in the amount of ¹⁴CO₂ generated from thiamine and the urinary excretion of thiamine and its metabolites. Higher ratios (8:1, 10:1) had less effect. Oxythiamine yielded only about half as many urinary metabolites as thiamine. One product of oxythiamine metabolism appears to be thiamine itself but the amount converted is extremely low and is of no apparent benefit to the rat.