[Presence in the rat of a genetic control of DAB-carcinogenesis]

Functional changes in rat liver mitochondria on administration of 2-methyl-4-dimethylaminoazobenzene

Administration of 2-methyl-4-dimethylaminobenzene in the diet (0.1%, w/w) for 85-90 days doubled the content of mitochondria in the livers of rats. The azodye was covalently bound to liver proteins, and about 15% of the amount found in liver was associated with the mitochondrial fraction. Mitochondria isolated from the livers of azodye-fed animals showed drastically lowered ability to oxidize NAD+-linked substrates. The inhibited electron-transfer step was the reduction of ubiquinone. The organelles showed a large increase in succinate oxidase activity. The activity of cytochrome oxidase and the content of cytochrome aa3 were substantially higher in these organelles. Azodye-fed animals showed depressed serum cholesterol concentrations. The content of ubiquinone in liver also registered a small increase.

N,N-diethyl-4-aminoazobenzene (DEAB): acute actions with respect to possible carcinogenicity as well as the role of solvents. Morphological and pharmacological investigations

The acute action of the azo dye DEAB was investigated in Sprague-Dawley (SD) and Wistar (Wi) rats. The substance was dissolved both in DMSO and sunflower oil and was administered once by stomach tube. Cytochrome P-450-DEPENDENT N-demethylation of ethylmorphine and dimethylnitrosamine are differentially altered depending on the solvent used. The excretion of DEAB as well as of N,N-dimethyl-4-amino-azobenzene (DAB) is delayed and diminished if the substances are dissolved in DMSO. Beside these effects the mitotic number in the adrenal cortex is significantly elevated in both strains of rats. But, in SD rats only DMSO-solution of DEAB is effective. In Wi rats both are effective, the oily solution more than that in DMSO. In this respect DEAB resembles DAB and various other carcinogens which are efficient in stimulating adrenocortical cell division. Considering the positive short-term assay after three other substances which revealed carcinogenic properties in long-term experiments we conclude that also DEAB may be carcinogenic in adequate long-term examination.

Dimethylnitrosamine-demethylase: molecular size-dependence of repression by polynuclear hydrocarbons. Nonhydrocarbon repressors

Studies with 58 polynuclear aromatic hydrocarbons have shown that to repress demethylation of dimethylnitrosamine (DMN) in rat liver, the hydrocarbons must satisfy specific requirements of molecular geometry regarding size, shape, and coplanarity. Expressing the molecular size of these planar compounds by the two-dimensional area occupied, the size for maximal repressor activity ranges between about 85 and 150 A2. In addition to being within the correct molecular size range the hydrocarbons must have an elongated-rather than compact-molecular shape; circularly shaped and/or highly symmetrical hydrocarbons, such as coronene, triphenylene, ovalene, and tetrabenzonaphthalene, have very low activity or are inactive, in spite of being in the optimum size range. Coplanarity of the molecule is a critical requirement; thus, the potent carcinogen, 9,10-dimethyl-1,2-benzanthracene, is inactive as repressor of DMN-demethylase synthesis. Two exceptions, fluoranthene and benzol[ghi] fluoranthene, showed significant induction of DMN-demethylase. The molecular size distribution of hydrocarbons that repress the DMN-demethylase shows a mirror-image relationship with respect to the earlier reported molecular size requirement for indcution of azo dye N-demethylase. Compounds other than hydrocarbons also show the mirror-image relationship in the sense that pregnenolene-16alpha-carbonitrile, alpha- and beta-naphthoflavone, and Aroclor 1254 (known to be inducers of various mixed-function oxidases) are strong repressors of DMN-demethylase. Aminoacetonitrile, a strong inhibitor of carcinogenesis by DMN, is also a potent repressor of DMN-demethylase. The enzyme is inhibited by pretreatment of the animals with cobaltous chloride, an inhibitor of the synthesis of cytochrome P-450. Pregnenolone-16alpha-carbonitrile and 3-methylcholanthrene, despite their similarity of action on DMN-demethylase, have different effects on azo reductase, which is repressed by the former and induced by the latter compound.