Effect of dietary phenobarbital on spontaneous hepatic tumorigenesis in germfree C3H/He male mice.

Phenobarbital (PB) is known to be a promoter of liver tumorigenesis in rats and mice. The present study was designed to examine the effect of PB on liver tumorigenesis in C3H/He germfree (Gf) male mice. Gf and conventional (Cv) animals were given an irradiated (5 Mrad) basal diet containing 200 ppm PB from 6 weeks old until termination of the experiment. When they were 12 months old, the animals were killed under CO2 inhalation and autopsied for the number and size of tumor nodules. The incidence of liver tumors was significantly higher in PB-fed Gf animals (67%) than in non-treated Gf controls (30%), and higher in PB-fed Cv animals (100%) than in non-treated Cv controls (75%). The number of tumor nodules per mouse was also significantly higher in PB-fed Gf animals (2.0) than in non-treated Gf controls (0.4), and higher in PB-fed Cv animals (4.5) than in non-treated controls (1.3). The present study demonstrated that dietary PB induced increases in number of the tumor nodules and decreases in the tumor size of C3H/He mice.