Germ-free and Conventional F344 Rats Promoting Effect of Bile Acids in Colon Carcinogenesis in

SUMMARY The promoting effect of sodium cholate or sodium cheno-deoxycholate on colon carcinogenesis was studied in fe male F344 germ-free and conventional rats. Both germ-free and conventional rats received intrarectal instillations of N-methyl-A/'-nitro-/V-nitrosoguanid¡ne (MNNG) for 2 weeks (total dose, 8 mg/rat) and then intrarectal doses of sodium cholate or sodium chenodeoxycholate (20 mg/rat/dose) three times a week for 46 weeks; other groups received MNNG for 2 weeks and vehicle thereafter for 46 weeks or bile acids alone for 48 weeks. Sodium cholate or sodium chenodeoxycholate increased MNNG-induced adenocarci-nomas and adenomas in germ-free rats, whereas in conven tional rats these bile acids induced more adenomas. Con ventional rats treated with MNNG + sodium cholate or MNNG + sodium chenodeoxycholate had a higher inci dence (p < 0.05) of colon tumors than did those given MNNG alone; germ-free rats that received MNNG + sodium cholate or MNNG + sodium chenodeoxycholate had a higher but not significant (p > 0.05) frequency of colon tumors than did those given MNNG alone. No tumors were detected in the colons of germ-free and conventional rats given sodium cholate or sodium chenodeoxycholate alone. It is concluded that sodium cholate or sodium chenodeoxy cholate had a promoting effect in colon carcinogenesis in rats evoked by MNNG.