Carcinogenresistance Mechanism in the Small Intestinal Tracts

Yoshiyuki Kurosaka

The Second Department of Surgery, Kanazawa University of Medicine

The small intestine is unique in its high resistance to tumor formation. To clarify the organ specificity of the carcinogenresistance of the small bowel, a segment of the ileum was interposed in the distal colon in male Wistar rats. The rats were administered MNNG at a dose of 2.5 mg/day via the rectum for 2 weeks from the second postoperative week. The rats were then intraperitoneally injected with IdU and BrdU at a 2-hour interval, and sacrificed 10, 20, 30, and 40 weeks after the operation. Control rats were given saline in a similar manner. Cell kinetic analysis of intestinal epithelium was performed by the double labeling method. The following carcinogenic rates were achieved: 0% for the saline group; 0% for the MNNG-treated group at 10 weeks, 54.5% at 20 weeks, 35.0% at 30 weeks, and 52.6% at 40 weeks. There was a significant difference in the site of cancer occurrence between the MNNG-treated groups. The carcinogenic rate in the interposed ileum was 3.3%, significantly lower than the 38.3% in the distal colon. Also the number of cancers per rat was 0.03 in the interposed ileum, significantly lower than 0.70 in the distal colon. The migration time of the MNNG-treated group was 91.4±21.1 hours in the distal colon and 40.6±8.2 hours in the interposed ileum. The epithelial cell migration time from the bottom of the crypt to the surface in the interposed ileum was significantly shorter than that in the distal colon. From these results, it was concluded that the rapid renewal rates of the small bowel epithelium cells was the principal carcinogenresistance mechanism of the small bowel.

Key words
cacinogen-resistance mechanism in the small intestinal tracts, interposed intestinal segment, N-methy1-N'-nitro-N-nitorosoguanidine, double labeling method, migration time of the intestinal epithelial cells

Reprint requests
Yoshiyuki Kurosaka The Second Department of Surgery, Kanazawa University of Medicine
13-1 Takaramachi, Kanazawa, 920 JAPAN

Accepted
September 8, 1993

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