In vitro development of zinc-deficient and replete rat embryos

The development of the zinc-deficient rat embryo has been studied in vitro using embryo culture techniques. Normal 9.5 day embryos cultured for 48 h in serum obtained from zinc-deficient rats grew and developed to the same extent as those cultured in zinc-replete serum. Embryos from dams which had been fed a zinc-deficient diet since mating were also removed for culture. Such zinc-deficient embryos fell into two broad morphological categories. One group appeared identical to the normal embryos, while the others had apparently normal visceral yolk sacs but small embryonic poles and retarded or abnormal embryonic development. Culture of the first group in either zinc-deficient or replete serum produced morphologically normal embryos; however, those which appeared abnormal at day 9.5 were grossly malformed after 48 h incubation in either sera. When embryos were cultured in the presence of 65Zinc, the most severely affected zinc-deficient embryos accumulated as much zinc as the zinc-replete and apparently unaffected zinc-deficient embryos, indicating that the malformations do not arise from an inability of the embryo or yolk sac to accumulate zinc from the surrounding fluid. The results from these studies suggest that the teratogenic effects of zinc deficiency cannot be induced by direct culture of zinc-replete embryos in zinc-deficient serum. Furthermore, it would appear that maternal zinc deficiency can exert its teratological influence prior to day 9.5 of gestation and that these effects are not readily reversible.