Metabolic fate of different inorganic and organic species of thallium in the rat

Different [^201+202Tl] labelled thallium compounds such as inorganic mono-(I) and trivalent Tl(III) ions as well as organic dimethylthallium (III) species have been prepared and administered intraperitoneally or orally to rats. The ^201+202Tl radioactivity was measured in the tissues as well as in the kidney and liver intracellular fractions such as nuclei, mitochondria, lysosomes, microsomes and cytosol. The results also suggest analogies in the metabolic behaviour of the dissimilar inorganic Tl⁺ and Tl³⁺ chemical forms when they were administered by different routes. Qualitative similarities have also been observed in the tissue distribution of inorganic Tl⁺ and Tl³⁺ and dimethylthallium forms, the latter being much less absorbed by the gastro-intestinal tract. However the renal and hepatic subcellular distribution of the organic dimethylthallium were identical with respect to those of the inorganic thallium-treated animals. The present findings suggest that the oxidation state of thallium does not influence its metabolism in vivo. The similar biochemical behaviour of the different thallium species is probably related to a mechanism which transforms the different species to a single form. At present it is not possible to predict the most probable oxidation state of thallium in vivo, because both Tl(I) and Tl(III) have been shown biochemically active in vitro.