Embryotoxic effects of methylmercuric chloride administered to mice and rats during orangogenesis.

Pregnant C57BL mice were given a daily dose of 7.5, 6.0, 5.0 or 2.5 mg/kg methylmercuric chloride (MMC) orally from the sixth through the thirteenth day of pregnancy. Pregnant Wistar rats were given a daily dose of 7.5, 5.0 or 2.5 mg/kg MMC orally from the seventh through the fourteenth day of pregnancy. Fetal examinations were performed on days 18 and 20 in mice and rats, respectively. In mice, the dose of 7.5 mg/kg was embryocidal. The dose of 6.0 mg/kg also caused a high incidence of fetal death, decreased fetal weight and a marked increase in malformations. A dose of 5.0 mg/kg caused a decrease in fetal weight and a marked increase in the incidence of malformations. The most common malformations were cleft palate and fused thoracic vertebrae. In rats, the dose of 7.5 mg/kg caused a high incidence of fetal death and malformations. The most frequent malformations were cleft palate, generalized edema, brain lesions and wavy ribs. A dose of 5.0 mg/kg caused a significant decrease in fetal weight and a significant increase in the incidence of malformations.