Induction of Aberrant Crypt Foci in the Large Intestine of F344 Rats by Oral Administration of 2‐Amino‐l‐methyl‐6‐phenylimidazo[4,5‐b]pyridine

Carcinogenicity of 2‐amino‐l‐methyl‐6‐phenylimidazo[4,5‐b]pyridine (PhIP) to rat colon was investigated using the appearance of colonic aberrant crypt (AC), a preneoplastic lesion, as a marker. The number of AC foci per colon at experimental week 4 was 1.3 ± 0.8; almost half the level of AC foci induced by 2‐amino‐6‐methyIdipyrido[l,2‐a:3′,2′‐d]imidazole (Glu‐P‐1), which is a known colon carcinogen. No ACs were observed in rats of the control group. A repeat experiment showed that induction of AC foci by PhIP administration was reproducible and a significant increase in the number of AC foci, 3.0 ±0.0, was observed after 12 weeks of PhIP administration. The majority of ACs induced by PhIP were localized in the distal part of the colon. The distribution was similar to those induced by Glu‐P‐1 and 1,2‐dimethylhydrazine. Those data suggested that PhIP is possibly carcinogenic to rat colon.