Abstract— The incorporation of 14C into amino acids of the brain was determined at different times after injection of [U‐14C]glucose and [U‐14C]ribose to rats maintained on thiamine‐supplemented and thiamine‐deficient diets for 22 days. The 14C‐content of amino acids in the brain of thiamine‐deficient rats decreased at times 2–10 min after injection of [U‐14C]glucose. but it increased at 2 min and decreased at times 5–10 min after injection of [U‐14C]ribose. The results of labelling of amino acids indicated that the activities in vivo of the thiamine pyrophosphate requiring enzymes, pyruvate oxidase, a‐oxoglutarate dehydrogenase and transketolase were similar in the two groups. It was suggested that the observed decrease in the labelling of amino acids was due to one or more of the following factors: (i) a decrease in the activities of glycolytic enzymes catalysing the conversion of glucose into triose phosphate; (ii) a decrease in the transport of substrate to the active site of the enzymes; or (iii) altered neurohistopathology of the brain. Thiamine deficiency in rats showed a 5% decrease in glutamate (P < 0–05), 46% decrease in threonine (P < 0001) and 16% increase in glycine (P < 0–01) content of the brain.

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