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Data from literature as well as the results of the author's investigations on the genotoxic and carcinogenic effects of sodium nitrite (SN) are presented. Carcinogenicity of SN detected in animal experiments proved to be connected with the formation of nitroso compounds from endogenous nitrosable precursors. Sodium nitrite possessed the transforming and promoting effects in the cell cultures as well as the mutagenic effects in the bacterial systems where predominant effect of SN as compared with N-nitrosodimethylamine (NDMA) was registered. The prolonged pretreatment with SN amplified the liver DNA damage in rats in case of NDMA endogenous synthesis.

Kidney tissue culture of 3-day old rats was cultivated in the presence of carcinogenic N-nitrosodimethylamine (NDMA), sodium nitrite, amidopyrine and a combination of these substances forming NDMA. All these substances induce changes in the number of DNA-synthesizing cells, monolayer density, percentage ratio of epithelial and fibroblastoid cells in the kidney cultures. The above changes are typical of each of the tested components, that permits using one-layer culture of the rat kidneys as a model for investigating cell response to the precursors of NDMA and to this carcinogen.

Lung tissue culture of 3-day old rats was cultivated in the presence of sodium nitrite, amidopyrine and combination of these substances with N-nitrosodimethylamine (NDMA). Each of these compounds produces specific changes in monolayer density, mitotic patterns and level of DNA synthesis in lung cell culture, which is considered to be convenient model for investigating cell response to the precursors of NDMA and to this carcinogen.

On the primary rat lung cell cultures, a study was made of the transforming action of sodium nitrite (NN) and amidopyrine combination with the control for formation of carcinogen--N-nitrosodimethylamine (NDMA) in growth medium. The manifestation of transformation was registered by appearance of morphological changes and multilayer growth foci. As criteria for evaluation after 48 hour treatments with NDMA, NN and AP, were used DNA-synthetizing activity of cells, mitotic index, frequency of mitoses pathology, monolayer density. The effects of transforming dose of NN alone and in combination with AP were the same. But malignization (tumor development in newborn rats in the points of cell suspension inoculation) took place only after administration of NN in combination with AP, when carcinogen was formed. Theophylline decreased the action of NN-AP combination.

After the long-term administration of doxilane-diolane, cresacin, antioxidant S-1 and fluorine varnish to mongrel albino rats and mice no difference in the level of spontaneous tumours both in the control and experimental groups of animals was observed. It is concluded that these drugs possess no carcinogenic activity.

Data obtained from the 10 year study of the spontaneous neoplasm incidence in mongrel mice and rats (males and females) from the colony of the R.E. Kavetskiĭ Institute for Oncology Problems are adduced. Spontaneous carcinogenesis was at an average 1:8 in mice (132 tumours per 1120 mice) and 1:3 in rats (93 tumours per 335 rats). Tumours of mammary glands and of pituitary prevailed in rat females.

By means of a semiquantitative antigenic analysis in the reaction of precipitation in agar with the use of a monospecific serum, obtained by the authors, dynamical changes have been studied in the content of the tissue-specific antigen in cells of subcutaneous connective tissue in rats: in the original and tripsinzed tissues, in 3, 6, 16-day and 1--2--3 month and malignized cultures, as well. It was found that at the 3, 11--13 day and then in 2--3 months of explantation there was a decrease in the content of the tissue-specific antigen, that is positively correlated with the degree of cell differentiation.

Mongrel rats of 12th day of pregnancy were administered sodium nitrite, amidopyrine, mixture of these substances and N-nitrosodimethylamine (NDMA) as well as alpha-tocopherol + ascorbic acid with drinking water. The cultivated lung cells of 3-day newborn rats with NDMA and its precursors were incubated. The transplacental effect of sodium nitrite on rat lung cells was observed. It was manifested in a decrease of the cell suspension viability, in an increase of the pathological mitosis level as well as in changes in cell responses to NDMA. The combination of sodium nitrite with phenobarbital considerably increased sensitivity of cells to the effect of NDMA, mixture of sodium nitrite with amidopyrine and amidopyrine.

The toxic and transformation actions of sodium nitrite (NN) were studied on the primary lung cell cultures of 3-day old noninbred rats. The monolayer density, mitotic index, DNA-synthetizing activity of cells, frequency of pathological mitoses changes in the character of growth, appearance of the multilayer growth foci serve as a criteria for evaluation. It is established that sodium nitrite has a transforming effect on lung cells and that the concentration of 1.035 mg/ml of nutrient medium is a transforming dose at 48 h exposition. Summation of the effect by prolongation of cell exposition with the NN prethreshold doses is possible.