Cadmium toxicity on mouse pre-implantation zygotes in vitro: interactions of cadmium with manganese, zinc and calcium ions.

Simultaneous treatment with cadmium chloride (5 micrograms/ml medium) and manganese chloride (5 or 10 micrograms/ml medium) was less toxic to mouse pre-implantation zygotes in vitro than cadmium alone. Such a protective effect of manganese, resembling that of zinc, suggests that amelioration of cadmium-treated pre-embryos in vitro is not unique to zinc. The amelioration may require only the presence of another divalent metallic ion, such as zinc or manganese, which is capable of competing with cadmium for binding sites possibly involved in uptake. Under calcium-free conditions cadmium embryotoxicity is enhanced, showing a summation effect of the cadmium toxicity and the lack of calcium. This supports the notion that excessive exogenous calcium may render the effects of cadmium on compaction inconspicuous. The non-compacted pre-embryos treated with 5 micrograms/ml cadmium in a calcium-free medium had fewer blastomeres than those treated at a lower dose of 1 microgram/ml. Cadmium appeared to inhibit the cleavage from 8-cell to 16-cell stage, but not from 4-cell to 8-cell.