Quantitative studies on the in vitro metabolic activation of dimethylnitrosamine by rat liver postmitochondrial...

The metabolic activation of dimethylnitrosamine (DMN) to mutagenic and/or cytotoxic intermediates in vitro has been characterized and the relationship between DMN demethylase and ethoxyresorufin-O-deethylase (EROD) or ethylmorphine-N-demethylase (EMND) has been evaluated. A mammalian assay system which uses the postmitochondrial supernatant (S-15 fraction) prepared from a rat liver homogenate as an enzyme source and V79 Chinese hamster cells as targets for chemically induced damage was used. The enzyme pattern of the S-15 fraction was altered by pretreatment of experimental animals in vivo and/or by the use of enzyme inhibitors in vitro. The results of these studies indicate that the concentration of S-15 fraction in the reaction mixture can markedly influence the degree of DMN-induced cytotoxicity when it is metabolized in vitro and that the degree of DMN-induced cytotoxicity and mutagenicity are linearly related. The degree of cytotoxicity and mutagenicity induced in V79 cells by DMN does not correlate with EROD activity (a measure of 3-methylcholanthrene-inducible mixed-function oxidases) nor with EMND activity (a measure of phenobarbital-inducible mixed function oxidases) in the S-15 fraction.