Tissue and Intracellular Distribution of Radioactive Thiamine in Normal and Thiamine-deficient Rats

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Abstract
The distribution of radioactive 14C-thiazole-labeled thiamine in intracellular fractions of rat liver, brain, kidney, and testes was studied in adult rats of the Sprague-Dawley strain that had been injected with physiological levels of thiamine for a long period of time. In all tissues 60 to 70% of the radioactivity was noted in the mitochondrial plus soluble fractions. About 20% of the radioactivity was present in the nuclear fractions from liver, kidney and testes but only 9% was found in this fraction from brain. Liver and kidney microsomal fractions contained 7 to 8% of the radioactivity, but 20 to 24% of the radioactivity in brain and testes appeared in this fraction. It is considered that mitochondrial contamination of the nuclear fractions prepared from liver, kidney and testes contributed some of the observed radioactivity in this fraction. The high thiamine content of the mitochondrial and microsomal fractions of brain may likewise be related to contamination with “pinched-off” nerve endings. During thiamine depletion the thiamine in the intracellular compartments depleted uniformly, i.e., no one compartment lost thiamine preferentially. The failure to observe a preferential depletion of thiamine from the soluble fraction of the cell was interpreted to mean that transketolase has a higher thiamine requirement than other enzymes requiring this co-factor or that the apoenzyme level itself was reduced.