Cogent epidemiological and experimental data implicate bile acids as endogenous co-carcinogens in colorectal cancer. A series of experiments was designed to test the ability of sodium deoxycholate (SDC) to promote intestinal hyperplasia and neoplasia in rats (n = 265). The intermediary role of faecal anaerobes was explored in animals receiving oral metronidazole. Intrarectal instillation of SDC trebled tumour yield in functioning large bowel and increased both crypt depth and crypt cell production rate. Metronidazole reduced this tumour promotion without affecting SDC-induced hyperplasia. By contrast, SDC was totally inactive in colon isolated as a Thiry-Vella fistula. Bile acids probably promote colorectal carcinogenesis by stimulating mucosal hyperplasia but only in the presence of faeces.
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