Inhibition of rat yolk sac pinocytosis by cadmium and its reversal by zinc.

The effect of cadmium on the in vitro pinocytic rate of 10- and 11-day-old rat yolk sacs grown on rat serum in culture was studied using the synthetic substrate 125I-labeled polyvinylpyrrolidone. In medium containing concentrations of added cadmium similar to those achieved in serum by intraperitoneal dosing of rats, the rate of pinocytosis in vitro was decreased by up to 55%. When zinc was included in the medium as well, the effect of cadmium was markedly reduced, and the rate of pinocytosis was restored to about normal. The results of this in vitro study suggest that cadmium can limit and supply of nutrients to the rat embryo in a nonspecific manner, and that elevated levels of zinc can restore the ability of the yolk sac to accumulate substances from the surrounding medium. Whereas cadmium may act as a teratogen at a number of sites, the demonstrated effect of this metal on the yolk sac provides a new insight into what could be a primary mode of action of cadmium on fetal development.