Metabolism of 35S-labelled copper-, zinc-and cadmium-thionein in the rat.

A comparative study has been made of the metabolism in the rat of intravenously-administered hepatic copper-, zinc- and cadmium-thioneins. In all cases the 35S-labelled protein was rapidly removed from the circulation. About 20% of the 35S was present in the kidneys after 30 min byt only small amounts of 35S were found in the liver, intestinal mucosa or pancreas. In the case of copper-thionein, 30% of the injected 35S was recovered in the urine within 2 h, mainly as intact copper-thionein. The 35S which appeared in the kidneys was also present initially as metallothionein but this was degraded very rapidly, especially when zinc-thionein was give. Both copper and cadmium from the injected proteins accumulated in the kidneys as metallothionein, but there was no increase in renal zinc concentrations in the rats dosed with zinc-thionein. These findings are discussed in relation to the development of renal damage in chronic cadmium and copper toxicity.