Studies on the metabolism of dimethylnitrosamine in vitro by rat-liver preparations. III. Effect of cobaltous chloride treatment.

1. The effects of CoCl2 administration to rats on xenobiotic metabolism, dimethylnitrosamine (DMN) metabolism to formaldehyde and methanol, and monoamine oxidase (MAO) enzyme activities in hepatic subcellular fractions have been studied. 2. CoCl2 treatment markedly decreased hepatic mixed-function oxidase enzyme activities and microsomal cytochrome P-450 content. In contrast, the N-oxidation of N, N-dimethylaniline and the activity of microsomal NADPH-cytochrome c reductase was unaffected. 3. The metabolism of DMN to formaldehyde by postmitochondrial supernatant fractions was decreased at substrate concn. of 0 . 5, 5 and 50 mM by CoCl2 treatment but the metabolism of 5 and 50 mM DMN to methanol was affected less. 4. CoCl2 had little effect on MAO activities in whole homogenates, but microsomal MAO activities were markedly inhibited. 5. The inhibition of microsomal MAO indicates that CoCl2 is not a specific inhibitor of cytochrome P-450-dependent biotransformations and consequently the inhibition of DMN metabolism is not evidence of a wholly cytochrome P-450-dependent process.

The excretion of metabolites of the D-glucuronic acid pathway in human urine. Effect of phenobarbitone administration.

1. The urinary excretion of four metabolites of the D-glucuronic acid pathway, namely D-glucaric acid, free (unconjugated) D-glucuronic acid, L-gulonic acid and xylitol, has been studied in normal male volunteers and in male and female epileptic patients receiving phenobarbitone anticonvulsant therapy. 2. In normal male subjects the urinary excretion of the D-glucuronic acid metabolites, expressed per unit of creatinine, was similar in first void and total (24 h) urine samples and was fairly constant over a period of 4 weeks. 3. In male and female epileptic patients phenobarbitone treatment enhanced the urinary excretion of D-glucaric acid and xylitol and the combined excretion of D-glucaric acid, l-gulonic acid and xylitol. 4. It is suggested that the measurement of a spectrum of urinary D-glucuronic acid metabolites may provide a more reliable index for assessment of the induction of hepatic xenobiotic-metabolizing enzyme activities in man than the determination of urinary D-glucaric acid alone.

Studies on the gastrointestinal absorption of N-nitrosamines: effect of dietary constituents.

Studies on the intestinal absorption of N-nitrosodimethylamine (DMN) in the rat have shown that the presence of dietary constituents such as fat markedly reduced the rate of disappearance of this nitrosamine whereas the presence of protein and carbohydrate had little effect on the absorption rate. Fat was also found to reduce the absorption rate of N-nitrosodiethylamine (DEN), N-nitrosopyrrolidine (NPY) and N-nitrosopiperidine (NPIP). Further it was confirmed that the small-intestinal tract of the rat has the ability to degrade DMN. The implications of these findings are discussed in terms of the biological fate of orally ingested nitrosamines.

The hydrolysis of flavouring esters by artificial gastrointestinal juices and rat tissue preparations.

The rates of hydrolysis of sixteen esters used as constituents of artifical flavours have been determined in artificial gastrointestinal juices and in fresh preparations of rat liver and small intestine. The artificial gastrointestinal juices exhibited a limited ability to hydrolyse the esters and of which methyl anthranilate was virtually uneffected. On the other hand, rat liver and small intestinal preparations were found readily to hydrolyse the esters to their component acids and alcohols. These findings showing large differences between the results obtained from the two methods suggest that use of tissue preparations is likely to produce data more relevant to the toxicological assessment of esters.