This experiment was conducted to study teratogenesis and carcinogenesis in relation to organogenesis, using the properties of short-action and high placental permeability of urethan.
Pregnant mice were exposed to urethan on various days of gestation (day 5 to 19) by a "single" injection, and malformations and neoplasms were induced in their offspring. Lung and tail anomalies were induced in 70-80% of the day 9 urethantreated group only, and this same group also developed a malignant teratoma. Pulmonary tumors were induced in high incidence in the groups exposed to urethan after day 13 of gestation. Embryological studies revealed that lung buds of mouse fetuses of this strain appeared on day 12. The same chronological relation was observed in induced hepatomas. Histologically, most of these pulmonary tumors were papillary adenomas. When the injection-parturition interval was short and late in term, pulmonary tumors were induced in higher incidence. Actual incidence of pulmonary tumors decreased in the day 19 urethan-treated group, when compared to that in the day 15 or 17 urethan-treated group. About one-third of mothers developed endometrial hyperplasia and hemangioma of uterine or placental origin.
When urethan was injected to lactating mothers, pulmonary tumors were induced in more than 50% of sucklings. This indicates that sucklings were exposed to urethan through the mother's milk.