Microsomal metabolism of the carcinogen, N-2-fluorenylacetamide, by the mammary gland and liver of female rats. I. Ring- and N-hydroxylations of N-2-fluorenylacetamide.

We determined ring- and N-hydroxylations of a systemic mammary gland carcinogen, N-2-fluorenylacetamide (2-FAA), by microsomal fractions of liver and mammary gland of female rats and the effects of in vivo and/or in vitro modifiers of these oxidations. Pretreatment of lactating rats with 3-methylcholanthrene (3-MC) or beta-naphthoflavone (beta-NF) and non-lactating (50-day old virgin) rats with beta-NF showed similar effects in that the formation of 3-, 5-, 7-, 9- and N-hydroxy-2-FAA by hepatic microsomes was increased manyfold and the formation of 1-hydroxy-2-FAA was induced. In mammary gland microsomes, the formation of 3-, 5- and 7-hydroxy-2-FAA was likewise increased, but of 9-hydroxy-2-FAA was unaffected. Only mammary microsomes of lactating rats had capacity for N-hydroxylation which was increased approximately 3 times by pretreatment of rats with 3-MC or beta-NF. All of the induced increases of metabolites of 2-FAA in hepatic and mammary microsomes were inhibited by 0.1 mM alpha-naphthoflavone (alpha-NF) in vitro. Pretreatment of non-lactating rats with phenobarbital increased only the formation of 7-hydroxy-2-FAA in hepatic microsomes which was further stimulated by alpha-NF in vitro. The latter also stimulated the formation of 7- and 9- hydroxy-2-FAA by hepatic microsomes of the uninduced rats, but had no effects in mammary microsomes, in which 9-hydroxy-2-FAA was a major metabolite. Hence, the data showed qualitative and quantitative differences between lactating and non-lactating rats in metabolism of 2-FAA by mammary microsomes which may result from differences in the levels (e.g., of cytochrome P-450) and activities of microsomal enzymes determined herein. In hepatic microsomes of these rats, differences in quantities of metabolites of 2-FAA (3-, 7-, 9- and N-hydroxy-2-FAA) were found in corn oil-treated rats only. The solvent (methanol or acetone) used for addition of 2-FAA to the incubation mixtures altered quantitatively the metabolite profiles in hepatic and mammary microsomes of 3-MC or beta-NF treated rats. The formations of 1- and 3- or 5- and 7-hydroxy-2-FAA were greater in the presence of acetone or methanol, respectively. The results of this study suggest that the formation of phenolic and N-hydroxy metabolites of 2-FAA in both hepatic and mammary microsomes of lactating rats is catalyzed by similar form(s) of cytochrome P-450 induced by pretreatment with 3-MC or beta-NF.(ABSTRACT TRUNCATED AT 400 WORDS)