Cadmium-thionein and the protection by cadmium against the nephrotoxicity of mercury.

Uptake of Hg2+ into the renal and hepatic metallothioneins of rats is increased by pretreatment with Cd2+. This increased uptake occurs both by displacement of Cd2+ (and of Zn2+) from the presynthesized cadmium-thionein, and by further synthesis of thionein. The former mechanism predominates in the kidney of the male rat, which is more sensitive than the female to Hg2+. The latter mechanism, which occurs particularly in the kidney of the female, also is considered to involve an initial displacement of Cd2+ from cadmium-thionein, but is followed by further synthesis of the metalloprotein, which is induced by the liberated cation. Pretreatment with Cd2+ increases not only the incorporation of Hg2+ into the renal metallothionein, but also the uptake of Hg2+ into other components of the kidney. At dose levels of Hg2+ at which Cd2+-pretreatment gives complete protection against the nephrotoxicity in male and female rats, the increase in Hg2+-uptake into both the particulate components and into the soluble fraction of the kidney is greater than into metallothionein. It is concluded, therefore, that binding of Hg2+ by pre-induced cadmium-thionein alone cannot explain the protection by Cd2+ against the nephrotoxicity of Hg2+.