An investigation of the role of metallothioneins in protection against the acute toxicity of the cadmium ion

Abstract

Pretreatment of female rats with a low dose of Cd 2+ protects them against a subsequent, normally lethal dose of the same cation, and also induces the synthesis of hepatic cadmium-thionein. This protection, however, 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 cadmium-thionein synthesis a greater percentage of a subsequent dose of Cd 2+ 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), however, is unaffected by the pretreatment. Although Cd 2+ is bound more strongly by the apoprotein, thionein, than is Zn 2+. pre-induction of hepatic zinc- thionein by restriction of food intake, does not lead to increased resistance to the toxic cation. These observations suggest that pre-induced metallothioneins do not have a significant role in the protection against the acute toxicity of Cd 2+.