Long-term turnover of cadmium metallothionein in liver and kidney following a single low dose of cadmium in rats.

Rats were injected subcutaneously on two consecutive days with CdCl2, and sampled animals, killed at monthly intervals from 1 to 6 months thereafter, exhibited the presence of Cd,Zn-thionein in both the liver and kidney. At 6 months, hepatic thionein was present as the two major polymorphic forms previously demonstrated in short term Cd-injection studies. [35S]cysteine incorporation studies showed that both polymorphic forms of thionein underwent continual turnover at similar rates throughout th study. The slow hepatic and renal turnover of Cd, therefore, was not due to a highly stable form of Cd-thionein, but apparently due to an inefficient mechanism for excretion of Cd from these tissues. The Cd/Zn ratio of hepatic thionein remained relatively constant, suggesting that continual thionein induction results in a long-term hepatic trapping of Zn by thionein, but the ratio of renal thionein showed a marked increase during the course of the study.