Carcinogenicity of methylated nitrosopiperazines in rats and hamsters

A comparison has been made of the carcinogenic activities of dinitroso-2,6-dimethylpiperazine (Me2DNP) and nitroso-3-4,5-trimethylpiperazine (Me3NP) in F344 rats and Syrian golden hamsters. The compounds were administered in drinking water to the rats and by gavage to the hamsters, at similar dose rates. As measured by the increased rate of mortality from tumors induced, Me2DNP was a more potent carcinogen in rats than Me3NP; Me2DNP induced mainly esophageal tumors, while Me3NP induced tumors of the nasal cavity, but no esophageal tumors. In contrast, in Syrian hamsters, by the same criterion, Me3NP was at least as potent as Me2DNP. Me3NP was more potent in hamsters than Me2DNP as measured by the number and multiplicity of tumors induced. The most numerous tumors induced by both compounds in hamsters were papillomas of the forestomach, but in addition Me3NP induced a high incidence of lung tumors. A small number of hamsters treated with either compound had liver angiosarcomas. Two hamsters given Me3NP had papillomas of the esophagus, a highly unusual tumor in Syrian hamsters.