INVESTIGATION OF ROLE OF METALLOTHIONEINS IN PROTECTION AGAINST ACUTE TOXICITY OF CADMIUM ION

Pretreatment of female rats with a low dose of CD2+ protects them against a subsequent, normally lethal dose of the same cation, and also induces the synthesis of hepatic Cd-thionein. This protection is maximal 1-3 days after pretreatment and then decreases, whereas both the increased content and capacity for the synthesis of the metallothionein are maintained. Because of this increased capacity for Cd-thionein synthesis a greater percentage of a subsequent dose of Cd2+ is retained in the liver of the pretreated animal than in the non-pretreated control. Uptake of the cation into other organs (i.e., heart, kidney, pancreas and spleen) is unaffected by the pretreatment. Although Cd2+ is bound more strongly by the apoprotein thionein than is Zn2+, pre-induction of hepatic Zn-thionein by restriction of food intake does not lead to increased resistance to the toxic cation. Pre-induced metallothioneins probably do not have a significant role in the protection against the acute toxicity of Cd2+.