Comparative carcinogenicity of two isomers of nitroso-2,6-dimethylmorpholine in guinea pigs.

The cis and trans isomers of nitroso-2,6-dimethylmorpholine (Me2NMOR) were administered by gavage to male Strain-2 guinea pigs as solutions in oil twice weekly for 30 weeks. Those animals treated with the cis isomer developed almost 100% incidence of liver tumors, together with tumors of the lung and adrenal cortex. In contrast, almost none of the animals treated with the trans isomer died with tumors. In rats, the trans isomer was considerably more potent than the cis, whereas this is not the result in guinea pigs, in which the cis is possibly more potent than the trans. This suggests that the mechanisms of activation in the 2 species might be different.