DNA ADDUCT FORMATION AND ASSESSMENT OF ABERRANT CRYPT FOCI IN-VIVO INTHE RAT COLON MUCOSA AFTER TREATMENT WITH N-METHYL-N-NITROSOUREA

N-Nitroso-compound DNA adduct formation in vivo and occurrence of aber rant crypt foci (ACF) were studied in the rat colon mucosa after a sin gle, local treatment with a carcinogen, N-methyl-N-nitrosourea (MNU), using a simple surgical approach. A segment of F344 rat colon was liga ted to make a pouch and injected with MNU solution. For the study of D NA adduct formation, the solution contained 50 mu Ci of [H-3]MNU. The results demonstrated that similar ranges of carcinogen dose, i.e. 0.15 x10(-2)-1.5x10(-2) M MNU, could induce both DNA adduct formation and a ppearance of ACF in the rat colon with both parameters showing a nearl y linear dose dependence. HPLC analysis revealed the DNA adducts to in clude both 7-methylguanine (7-mGua) and O-6-methylguanine (O-6-mGua) w ith the 7-mGua/O-6-mGua ratio being 8.2-11.3:1 in the system used. Ass essment of ACF development from 4 to 16 weeks after MNU treatment at a dose of 7.5 x 10(-2) M showed the numbers to increase up to the 8th w eek, followed by a decrease at weeks 12 and 16, when 40% of the ACF co unted at the peak time point were still present. The percentage of lar ge ACF (greater than or equal to 4 crypts/ACF) significantly increased with time. These results indicate a clear relation between DNA adduct s and preneoplastic lesions, i.e. ACF. In conclusion, DNA adduct forma tion and ACF can be efficiently and simply detected in vivo by using t he method described in the present paper.