RESTORATION BY IODIDE OF HEPATIC REACTIONS TO 2-AMINOFLUORENE IN THYROIDECTOMIZED RATS

Chemical carcinogens. A review and analysis of the literature of selected chemicals and the establishment of the Gene-Tox Carcinogen Data Base. A report of the U.S. Environmental Protection Agency Gene-Tox Program

The literature on 506 selected chemicals has been evaluated for evidence that these chemicals induce tumors in experimental animals and this assessment comprises the Gene-Tox Carcinogen Data Base. Three major sources of information were used to create this evaluated data base: all 185 chemicals determined by the International Agency for Research on Cancer to have Sufficient evidence of carcinogenic activity in experimental animals, 28 selected chemicals bioassayed for carcinogenic activity by the National Toxicology Program/National Cancer Institute and found to induce tumors in mice and rats, and 293 selected chemicals which had been evaluated in genetic toxicology and related bioassays as determined from previous Gene-Tox reports. The literature data on the 239 chemicals were analyzed by the Gene-Tox Carcinogenesis Panel in an organized, rational and consistent manner. Criteria were established to assess individual studies employing single chemicals and 4 categories of response were developed: Positive, Negative, Inconclusive (Equivocal) and Inconclusive. After evaluating each of the individual studies on the 293 chemicals, the Panel placed each of the 506 chemicals in an overall classification category based on the strength of the evidence indicating the presence or absence of carcinogenic effects. An 8-category decision scheme was established using a modified version of the International Agency for Research on Cancer approach. This scheme included two categories of Positive (Sufficient and Limited), two categories of Negative (Sufficient and Limited), a category of Equivocal (the evidence of carcinogenicity from well-conducted and well-reported lifetime studies had uncertain significance and was neither clearly positive nor negative), and three categories of Inadequate (the evidence of carcinogenicity was insufficient to make a decision, however, the data suggested a positive or negative indication). Of the 506 chemicals in the Gene-Tox Carcinogen Data Base, 252 were evaluated as Sufficient Positive, 99 as Limited Positive, 40 as Sufficient Negative, 21 as Limited Negative, 1 as Equivocal, 13 as Inadequate with the data suggesting a positive indication, 32 as Inadequate with the data suggesting a negative indication, and 48 Inadequate with the data not suggesting any indication of activity. This data base was analyzed and examined according to chemical class, using a 29 chemical class scheme.(ABSTRACT TRUNCATED AT 400 WORDS)

Enhancement of hepatic and renal tumorigenesis with thyroidectomized NZR/Gd rats treated with dimethylnitrosamine

Endocrine modulation of DMN carcinogenesis was studied in NZR/Gd rats preconditioned by starving 48 hr and then injected i.p. once with 20 mg DMN/kg. Intact rats developed kidney tumors (44% TBA), most of tubular epithelial type resembling human tumors rather than mesenchymal. Thyroidectomy (Tx) 45 days before DMN significantly enhanced DMN carcinogenesis, renal carcinoma incidence increasing to 69%. Renal carcinomas showed more signs of malignancy in Tx rats. Other neoplastic responses useful for further studies including tumors in nasal epithelium (13%), liver (18%, increased to 59% in Tx rats), and lung (40%): these tumors were rare or not previously reported in single-dose experiments in other rat strains. A sex difference in lung tumor incidence (male 70%, female 16%) was statistically significant and thyroidectomy reduced the sex-differential (to 54% and 39% respectively). The increased incidence of kidney and liver tumors could be due to altered metabolism of DMN in tissues of Tx rats.