Tumor development in lung of ddY mice following transplacental exposure to 1-ethyl-1-nitrosourea.

Transplacental induction of lung tumor by 1-ethyl-1-nitrosourea (ENU) was studied in pregnant ddY mice which were given a single intraperitoneal injection of 58.5 mg/kg of ENU in water between day 13 and 19 of gestation. Within 4 approximately 6 weeks after birth, pulmonary tumor nodules were found in all offsprings exposed to ENU, and they were histopathologically adenoma. Number of tumor nodules could be counted under the stereomicroscope from approximately day 40 after birth. The size of tumor increased with the lapse of time but the number of tumor nodules did not increase markedly. Weekly injections of urethan or ENU into mice pretreated with ENU in their fetal age enhanced the number of pulmonary adenoma. The development of other tumor was not seen except a few cases of lymphoma. Tumor development in the lung by injection of ENU in ddY mice during gestation is reproducible, relatively simple, and rapid. Therefore, it is considered that this may be a useful method for screening of antitumor agent.