Pregnancy-induced mobilization of copper and zinc bound to renal metallothionein in cadmium-loaded rats

Our investigations undertook to examine whether copper (Cu) and zinc (Zn) bound to renal metallothionein (MT) along with cadmium (Cd) in Cd-loaded rats can be mobilized during pregnancy and lactation. Rats of the Wistar strain were injected with Cd. Synthesis of MT containing Cd, Cu and Zn was induced in the kidneys. Concentrations of Cd and essential elements in blood plasma and organs (liver and kidneys) were compared among non-pregnant and pregnant, and Cd-loaded and non-loaded rats at middle and late gestational days and after delivery. Cu bound to renal MT was decreased with gestational age, while Zn was slightly increased. The results indicate that Cu was mobilized and utilized even when the metal was bound to MT in the kidneys of dams. On the other hand, Zn bound to renal MT in Cd-loaded rats was retained and not mobilized during pregnancy. The elution profile of renal MT on an SW column was changed from a typical renal to a mixed profile of renal and hepatic MTs as a result of decreased Cu content in MT. Plasma essential elements changed similarly with gestational age in both concentrations and distributions in non-loaded and Cd-loaded rats. These results indicate that the 3 metals bound to renal MT are dealt with differently during gestation and lactation, and Cu but not Zn is transferred to the fetus, independently of the Cd status of the dam.