EFFECT OF DAY OF EXPOSURE ON THE DEVELOPMENTAL TOXICITY OF MANGANESE IN MICE

Manganese is embryotoxic and fetotoxic in mammals. The aim of this stu dy was to determine whether the day of exposure would modify the devel opmental toxicity of manganese (II). Pregnant Swiss mice were given si ngle sc doses of 50 mg manganese chloride tetrahydrate/kg on day 9, 10 , ii or 12 of gestation. No maternal deaths, abortions or early delive ries were observed. Dams were killed on gestational day 18 and the ute rine contents examined. Embryotoxicity, evidenced by significant incre ases in number of late resorptions and in percentage of postimplantati on loss, was especially relevant in groups dosed on gestational days 9 or 10. Fetotoxicity (reduced fetal body weight and increased incidenc e of skeletal defects) was also especially remarkable from doses on da ys 9 or 10 of gestation. However, no teratogenic effects were noted in any group. Although mouse conceptus are adversely affected by sc expo sure to manganese on any of the gestational days 9-12, days 9 and 10 o f gestation are the most sensitive for manganese-induced embryo/fetal toxicity in mice.