Effect of phenobarbital on induction of liver and lung tumors by dimethylnitrosamine in newborn mice.

The effect of phenobarbital on simultaneous induction of liver and lung tumors was examined in inbred DDD mice. Group 1 of newborn mice received a single intraperitoneal (ip) injection of dimethylnitrosamine (DMN) and after weaning they were given 0.05% phenobarbital solution to drink. Group 2 received an injection of DMN like Group 1 but were then given normal water. Group 3 were injected ip with 0.9% NaCl solution and then given phenobarbital solution to drink as in Group 1, and Group 4 were injected with 0.9% NaCl solution like Group 3, and then given tap water to drink. The animals were examined 16 weeks after birth. In Group 1, 27 of 35 mice (77%) had liver tumor and 15 (43%) had lung tumor. In Group 2, 8 of 24 mice (33%) had liver tumor and 16 (67%) had lung tumor. Animals in Groups 3 and 4 did not develop tumors. The difference in the incidences of liver tumor, but not lung tumor, in Groups 1 and 2 was statistically significant (P less than 0.01); that is, a promoting effect of phenobarbital was observed in induction of liver tumor, but not lung tumor.