Male Wistar rats weighing 100 g received 1,2-dimethylhydrazine (25 mg/kg) s.c.) twice a week for 2 months and once a week thereafter for an additional 4 months. Groups of four to six rats were sacrificed monthly. Paraffin sections of duodenum were prepared and stained with periodic acid-Schiff and hematoxylin for cell counts and with toluidine blue for measuring nucleolar area. As an index of villus size and crypt size, the mean number of epithelial cells per representative sections of villi and crypts were used. Mitotic activity was assessed by counting the mean number of mitotic figures per representative crypt section. Nucleolar area was assessed from the analysis of drawn (camera lucida) images of nucleoli of columnar cells at six levels of the epithelium: lower, mid, and upper parts of the crypts and villi. Villus size increased progressively during the 6-month treatment, from 272 ± 2 (S.E.) to 349 ± 8. Crypt size increased from 118 ± 2 in a wavy fashion, showing maximum (139 ± 5, 143 ± 2) at 3 and 6 months and minimum (123 ± 3, 127 ± 1) at 1 and 4 months. Mitotic number displayed a similar pattern of increase so that the percentage of mitotic figures in the crypts (mitotic index) remained constant (about 5%) in control and experimental animals. Nucleolar area in the controls decreased with age from 4.2 ± 0.08 sq µm in lower crypt at 1 month to 2.8 ± 0.04 sq µm at 6 months. During 1,2-dimethylhydrazine treatment, lower crypt nucleoli increased to 4.5 ± 0.12 sq µm after 3 months and decreased slightly thereafter, reaching 4.0 ± 0.14 sq µm by the sixth month. The nucleoli furthermore decreased gradually along epithelium (nucleolar compaction) by an average of 0.23% per cell position in control as well as treated animals. It appeared, then, that the main effect of 1,2-dimethylhydrazine was the enlarging of the four parameters measured. This effect seemed to relate in some manner to tumor formation as all the enlargements were attenuated in intestinal tissue adjacent to tumors.

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Partially supported by the Medical Research Council of Canada and by the National Cancer Institute of Canada.

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