Effects of low dose mixtures of four N-nitroso compounds on hepatic foci development in the rat (original) (raw)

Potential synergism between four N-nitroso compounds (nitrosomorpholine, nitrosodimethylamine, nitrosodiethanolamine, nitroso-oxazolidine) in rat liver carcinogenesis was examined in the medium-term bioassay. Mage F344 rats were initially given diethylnitrosamine (DEN, 200 mg/kg, ip) and beginning 2 weeks later received test chemicals for 6 weeks individually at a full or l/4 dose of that proven to be carcinogenic individually or in combination. All animals ware subjected to partial hepatectomy at week 3 and killed at week 8. Induction of immunohistochemically-demonshated glutathione Stransferase placental form (GSTP) positive foci was evaluated. The numbers and size of GST-P positive foci were significantly higher than the control levels by the treatment with each nitrosamine at full (l/l) and one quarter doses (114), excepting nitrosodiethanolamine and by combination of the four chemicals at l/4 and l/16. Because the dose-response curves were considered non-linear for most nitrosamines, synergistic effects were not apparent for the l/4 mixture. In~~st~~~, however, the values for rats treated with these four chemicals in combination at the l/4 dose level were almost the same as the average of four individual treatments at the full dose, and those for the l/16 dose mixture were almost the same as the average of l/4 individual treatment groups. These results indicate that these nitrosamines worked additively, rather than synergistically, in rat liver carcinogenesis.