Abstract
We examined the growth characteristics of dimethylhydrazine (DMH) -induced colon cancer in rats. Sprague-Dawley rats received 10 weekly s. c. injections of DMH at a dose of 40 mg/kg to induce colon cancer. At 22 weeks after the start of DMH treatment, barium enema was performed to visualize colon tumors. At five weeks, barium enema was repeated, and then an autopsy was performed. Tumor volume was calculated from both films and tumor doubling time was estimated. A total of 30 tumors were found at autopsy, which were fixed, sliced, and stained with PCNA to calculate the labeling index (LI) . The PCNA LI differed depending on the location of the tumor in thecolon. The PCNA LI of the upper area of the colon cancer (38.8±4.5%) was higher than that of the lower area in the same tumor (24.6±7.4%) (p<0.01) . In pathological studies, the PCNA LI did not correlate with histological type or with presence of lymph metast asis. PCNA LI also showed different regional staining in the normal mucosa in the colon, with a higher PCNA LI in the lower area in the colon (26. 9 ± 5.7 %) than in the upper area in the same location (13.5±6.1%) (p<0.01) . The upper area of colon tumors may therefore better reflect the growth characteristics of DMH-induced colon cancer in rats, because the tumor doubling time correlated well with the PCNA LI in this region.
