[Chemoinduced early precancerous colonic lesions in rats].

The aim of this study was to investigate the early histological changes during 1.2-dimethylhydrazine-induced carcinogenesis in the rat, and to search for a dose-response relationship. Thirty Wistar female rats received 1.2-methylhydrazine 15 mg/kg sc, weekly in a single injection, and were sacrificed after 1 to 9 weeks. The left portion of the colon was cut serially (300-350 sections per animal) and was then submitted to a routine histochemical study with 18 stains. Loss of mucous secretion and apical basophilia lesions were observed as early as the 2nd week. The rate of apical basophilia lesions, expressed in percentage of the total number of lesions, was significantly correlated with the total dose of carcinogen administered (p less than 0.001). The severity of the lesions (expressed as the logarithm of the total number of sections showing altered tubes) increased with the dose, first quickly, then more slowly afterwards. A significant correlation was observed between the site, as defined by the distance from the anal verge and the severity of the injuries (p less than 0.001) as they were located more proximally as the doses increased. The comparison of the results obtained from this series of animals sacrificed early and those from a former series with spontaneous survival, suggests that only 2 p. 100 of the apical basophilia lesions should develop macroscopic lesions (polyps or cancers). Hence, it is advisable to consider the chronology and the site of the sampling in order to interpret apparently divergent series.(ABSTRACT TRUNCATED AT 250 WORDS)