Pregnancy-associated changes in plasma metallothionein concentration and renal cadmium accumulation in rats

Pregnancy-associated changes in metallothionein (MT) concentrations in blood plasma were examined using a competitive enzyme-linked immunosorbent assay with a rabbit polyclonal antibody to rat liver MT. Plasma MT of pregnant rats significantly increased after 8 days of gestation and remained high during pregnancy and for 7 days after delivery. Gel filtration showed that both Cu and Zn were associated with the plasma MT of pregnant rats. These results suggest that plasma MT may play a role in the transport of essential metals such as Cu and Zn to fetus during pregnancy, but the source of plasma MT is unknown. Injections of cadmium chloride and cadmium-metallothionein to pregnant rats further increased the plasma MT concentrations. After injection of CdCl2, both MT and Cd concentrations in the liver of the pregnant rats were significantly lower than those of the nonpregnant rats, whereas renal Cd and MT levels were higher in pregnant rats. This increased accumulation of Cd in the kidney of pregnant rats may be related to the increase of plasma MT during pregnancy. About 5% of 6 pg of in vitro added Cd (20 pg/ml) was bound to the MT in the plasma. Therefore, Cd may be transported by the circulating MT to the kidney, leading to an increase in renal accumulation of Cd in pregnant rats.