Comparison of Faecal and Intestinal Concentrations of Granulocyte Marker Protein and Localization of Gastrointestinal Tumours in Rats

Abstract

Background: Increased faecal concentrations of the granulocyte marker protein (GMP) have been found in rats with azoxymethane (AOM) induced carcinoma of the colon, but the origin of this GMP is unknown. The aims were to investigate the concentrations of GMP in different parts of the gastrointestinal (GI) tract in rats with or without AOM-induced carcinoma and to correlate the GMP concentrations to localization of the carcinomas. Methods: Nineteen rats were given intramuscular injections of AOM, 15 mg/kg, once weekly for 6 weeks and were killed after 22 weeks. Five rats that were not given AOM injections served as controls. Results: All rats given AOM developed tumours; 18 developed a total of 33 adenocarcinomas in the GI tract and one developed an adenoma in the colon. Nine animals had carcinoma in the small bowel, seven of which also had carcinoma of the colon, and nine animals had carcinomas in the large bowel only. No other tumours were found. All except one of the animals that had carcinoma of the colon had elevated faecal GMP concentrations, and from week 11 there was a significant difference in the GMP values between the control group and the group that developed colon carcinoma. In all rats that developed carcinoma in the small bowel, the tumour was localized in the proximal part. In the rats that had been given AOM, the luminal GMP concentrations were significantly higher in the proximal part of the small bowel than in the distal part, but there were no significant differences in the GMP concentrations between animals with and without carcinoma in the small bowel. Sixteen rats developed a total of 24 carcinomas in the colon, and one rat developed an adenoma. Luminal GMP concentration in the distal part of the colon was elevated in all animals with carcinomas in the colon, and the GMP concentrations were significantly higher in the distal part than in the proximal part. Rats with one carcinoma in the colon had significantly lower GMP values in the distal part, compared to rats that had two carcinomas in the colon. Conclusions: The animal model described is suitable for further studies on many aspects of tumour development in the colon. Furthermore, it is likely that increased faecal GMP concentration in rats with colon carcinoma is a result of an inflammatory process in or around tumours.