Phenobarbital enhances the formation of reactive oxygen in neoplastic rat liver nodules

The effect of treatment of rats with the liver monooxygenase inducer phenobarbital on the formation of reactive oxygen in neoplastic liver nodules and the surrounding normal tissue was investigated. Liver nodules were induced by treatment of rats with diethylnitrosamine (single i.p. injection of 0.15 mumol/kg body weight on day 1 after birth) followed by chronic administration of phenobarbital-sodium (PB; 0.05% in diet) after weaning. Groups of rats were kept on PB until sacrifice or were withdrawn from the promoter 3-6 weeks prior to killing. Emission of chemiluminescence was used as a sensitive means to detect the formation of reactive oxygen in microsomal preparations from the various tissues incubated with NADPH and the chemiluminigenic detector lucigenin. In addition, a 2-dimensional photon counting system has been developed that permits the analysis of the spatial distribution of lucigenin-chemiluminigenic signals over liver tissue sections incubated with reduced phosphopyridine dinucleotides. In general, we observed increased levels of reactive oxygen formation in liver nodules when compared with the normal liver tissue. Highest levels were seen in nodules that stemmed from PB-induced rats. Studies on the expression and activity of cytochrome P-450 in liver nodules as well as experiments with specific inhibitors point towards a participation of the liver monooxygenase system in reactive oxygen formation, although additional metabolic pathways seem to be involved as well. The observed increases in reactive oxygen in liver nodules of PB-treated rats might be related to the promoting activity of this drug.