Oxidative dealkylation and reductive denitrosation of nitrosomethylaniline in vitro.

N-Nitrosomethylaniline (NMA) was incubated with liver microsomes from female mice and rats. Both formaldehyde and nitrite formation were determined in the same incubation mixture under various experimental conditions. The animals were pretreated with phenobarbital (PB) or butylhydroxytoluene (BHT) in order to modify microsomal monooxygenase activities. Furthermore, various possibilities were tried to supply the microsomal system with reducing equivalents (NADPH-regenerating system, NADPH-regenerating system plus NADH or NADH alone). It can be deduced from these experiments that both enzymatic activities--oxidative demethylation and reductive denitrosation of NMA--do not proceed in a parallel manner. Thus both reactions are different from each other. They represent two separate pathways in nitrosamine metabolism.