Dimethylnitrosamine, dipropylnitrosamine, methylethylnitrosamine, nitrosopiperidine and nitrosopyrrolidine were assayed for mutagenicity in the Ames test in the presence of hepatic postmitochondrial preparations isolated from the mouse, rat, hamster, pig and man. Prior to each mutagenicity assay all activation systems were fully characterised with respect to monoamine oxidase, mixed-function amine oxidase and mixed-function oxidase activities. The hamster was the most efficient activator for all nitrosamines followed by the mouse. The latter species, however, activated nitrosopyrrolidine only weakly which was the only carcinogen readily activated by the human preparation. None of the aliphatic nitrosamines was activated by the rat or pig. No correlation was observed between efficiency of activation and any of the enzyme activities studied.

Three enzymes used for the determination of cytochrome P-448 activity, namely aryl hydrocarbon hydroxylase, biphenyl 2-hydroxylase and ethoxyresorufin O-de-ethylase, were evaluated with respect to their specificity, sensitivity and inducibility. Purified cytochrome P-448 (LM4), but not cytochrome P-450 (LM2), catalysed the O-de-ethylation of ethoxyresorufin in a reaction that was markedly inhibited by 9-hydroxyellipticine. After the administration of 3-methylcholanthrene to rats all three activities were induced, the extent of induction being highest for ethoxyresorufin O-de-ethylase. Administration of very small doses of benzo[a]pyrene (50 micrograms/kg) to rats to induce cytochrome P-448 specifically increased only the O-de-ethylation of ethoxyresorufin. 3-Hydroxybenzo[a]pyrene, the major metabolite determined by the aryl hydrocarbon hydroxylase assay, undergoes further NADPH-dependent oxygenation leading to loss of fluorescence. On the basis of these observations and those by other workers, we conclude that ethoxyresorufin O-de-ethylase provides the most specific, sensitive and reproducible means of determining cytochrome P-448 activity.

No abstract

No abstract

No abstract