Kinetics of sister-chromatid exchange induction by different carcinogens in C57BL/6J and DBA/2 mice.

Sister-chromatid exchange (SCE) levels were determined in bone marrow cells of DBA/2 and C57BL/6J mice at 18, 24, 30 and 48 h after treatment with 10 mg/kg cyclophosphamide (CP), 300 mg/kg urethane or 25 mg/kg N-nitroso-N-methylurea (NMU). DBA/2 mice showed higher SCE frequencies than C57BL/6J mice at all time points examined after CP and urethane treatment, whereas NMU administration resulted in similar SCE levels in both strains. After CP and urethane treatments, SCE values reached the highest level at 18 h, were similarly high at 24 and 30 h, and returned to base-line level at 48 h. In NMU-treated mice, the SCE values had the same level at 18, 24 and 30 h and returned to normal at 48 h. The results are interpreted as indicating that different metabolic capabilities are responsible for the difference in SCE response in the two strains.