Lack of promotion effect of phenobarbital on pulmonary tumorigenesis in ddy mice initiated by transplacental exposure to 1-ethyl-1-nitrosourea.

The promoting effect of phenobarbital (PB) on lung tumorigenesis in mice was examined. Pregnant ddy female mice were injected ip with a single dose of 50 mg/kg 1-ethyl-1-nitrosourea at the 16th day of gestation. Offspring, 160 in total, were divided into two groups: one group of animals was fed a diet containing 0.05% PB continuously and the other was kept on the basal diet. All the animals were killed at 6 months of age and the number, size and histology of pulmonary tumors were examined. There were over 10 pulmonary tumors per animal on average, measuring from 0.5 to 10.2 mm in size, and the histology varied from grade I to III in atypism. A comparative study revealed no difference between PB-treated and control mice in any aspect of the tumorigenesis. It was concluded that PB does not have promoting effect on pulmonary tumorigenesis in this system.