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Enhanced carcinogenesis in the proximal small intestine of the rat following rumenectomy.

Various techniques have been used to enhance carcinogenesis in experimental animals. This study examines the effects of the excision of the forestomach (rumen), a squamous epithelial pouch of the rat, on the incidence and distribution of intestinal neoplasms induced by 1,2-dimethylhydrazine (DMH). Thirty-four male Sprague-Dawley rats were randomly assigned to control and experimental groups. The experimental group was subjected to an excision of the rumen while the control group underwent a gastro-rumenotomy and closure. Following a two week recovery period, each animal was weighed and injected with DMH (20 mgm/kg body wt) on a weekly basis for 22 weeks. At 24 weeks, the 32 surviving rats were sacrificed and the number, location, and histology of the neoplasms in the intestinal tract of each rat were noted. Rumenectomy resulted in a statistically increased incidence of neoplasms in the proximal small bowel (mean of 1.3 +/- 0.01 neoplasms/rat) when compared with the control group (mean of 0.1 +/- 0.2 neoplasms/rat) (p less than 0.001); but did not influence the incidence, distribution, or histology of colonic neoplasms between control and experimental animals. All neoplasms of the proximal small bowel when examined histologically were classified as invasive adenocarcinomas. The colon contained adenomata and carcinoma in situ, as well as adenocarcinomas. It is therefore concluded that excision of the rumen of the rat stomach selectively promotes malignant formation in the proximal small bowel following repeated injections of DMH.