Phenobarbital lacks promoting activity for neurogenic tumors in F344 rats transplacentally exposed to ethylnitrosourea.

A chronic rodent study in F344 rats was conducted to investigate the promoting ability of phenobarbital (PB) on neurogenic tumors initiated by transplacental administration of ethylnitrosourea (ENU). Pregnant F344 rats were given a single intravenous dose of 3.5 mg ENU/kg or vehicle on the twentieth day of gestation. A total of 192 male offspring were divided into four groups: ENU-PB, ENU-control, PB-control, and control-control. Rats in ENU-PB and PB-control groups received 0.05% PB in their drinking water from four to 78 weeks of age. Nervous system tumors were induced only in animals exposed to ENU. The difference in the incidence of neuroectodermal tumors in rats that were ENU initiated only (13/37; 35%) compared to the incidence in rats that were initiated and given PB (13/57; 23%) was not statistically significant (p greater than 0.05). ENU-control and ENU-PB treatment groups exhibited no differences in tumor multiplicity or tumor latency. These results demonstrate that PB lacks promoting activity for neurogenic tumors in F344 male rats transplacentally exposed to ENU.