Role of hepatic metallothionein during perinatal development in the rat.

The concentration of metallothionein (MT) in the liver of the perinatal rat is relatively high at term and 7 days after birth and then decreases to barely detectable levels by day 28. The developmental pattern MT-zinc parallels that of MT. When challenged with a single injection of cadmium chloride, the 26-day-old rat responds with a dose-related increase in hepatic MT which sequesters both cadmium and zinc. When the 5-day-old rat is similarly challenged, induction of MT occurs only at the highest dose tested (6 mg Cd/kg); however, due to the pre-existence of MT in these younger rats, cadmium administered at the lower doses still binds to the MT in a dose-related manner. Despite the induction of MT seen in both age groups following the 6.0 mg/kg dose, exposure to that level of the metal produced death in 30% of the younger animals but in only 4% of the older animals. When cadmium was administered to pregnant rats on day 19 of gestation, it was found to produce a dose-related induction of maternal hepatic MT over the following 48 hr. In contrast, maternal exposure to the metal led to a significant depression of fetal hepatic MT over the same time interval.