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Comparative carcinogenicity of two isomers of nitroso-2,6-dimethylmorpholine in guinea pigs
Abstract:
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.
Insights
The cis isomer of nitroso-2,6-dimethylmorpholine (Me2NMOR) caused high rates of liver, lung, and adrenal tumors in guinea pigs. The trans isomer showed significantly less tumor development, suggesting different activation mechanisms between species.
Area of Science:
- Toxicology
- Carcinogenesis
- Comparative Oncology
Background:
- Nitroso-2,6-dimethylmorpholine (Me2NMOR) is a chemical compound with known toxicological properties.
- The cis and trans isomers of Me2NMOR may exhibit differential biological activity and carcinogenic potential.
- Understanding species-specific responses to chemical carcinogens is crucial for risk assessment.
Purpose of the Study:
- To investigate the carcinogenic effects of cis and trans isomers of Me2NMOR in male Strain-2 guinea pigs.
- To compare the tumor incidence and types induced by each isomer.
- To explore potential differences in metabolic activation pathways between guinea pigs and rats.
Main Methods:
- Male Strain-2 guinea pigs were administered cis or trans isomers of Me2NMOR via oral gavage.
- Treatment was conducted twice weekly for a duration of 30 weeks.
- Tumor incidence, type, and location were monitored in the treated animals.
Main Results:
- Administration of the cis isomer of Me2NMOR resulted in a nearly 100% incidence of liver tumors, along with lung and adrenal cortex tumors.
- Animals treated with the trans isomer exhibited a significantly lower incidence of tumors.
- A notable difference in isomer potency was observed compared to rats, where the trans isomer is more potent.
Conclusions:
- The cis isomer of Me2NMOR is a potent carcinogen in guinea pigs, inducing tumors in multiple organs.
- The trans isomer of Me2NMOR demonstrates significantly weaker carcinogenic activity in this species.
- Discrepancies in isomer potency between guinea pigs and rats suggest species-specific metabolic activation pathways for Me2NMOR.