Comparison of sister chromatid exchanges in spleen and thymus lymphocytes from AKR, C57BL/6N x DBA/2J F1, and CBA mice following in vivo exposure to N-methyl-N-nitrosourea.

The induction of sister chromatid exchange (SCE) by N-methyl-N-nitrosourea (MNU) was studied in spleen and thymus lymphocytes from AKR mice, which are highly susceptible to MNU-produced thymomas, CBA mice, which are much less sensitive to induction of thymomas by MNU, and C57BL/6N x DBA/2J F1 mice. MNU produced dose-related increases in SCE in concanavalin A (Con A)- and lipopolysaccharide-stimulated spleen lymphocytes and Con A-stimulated thymus lymphocytes from each mouse strain at 1 and 24 h posttreatment. MNU-induced SCE were generally higher in Con A-stimulated spleen lymphocytes compared to lipopolysaccharide-stimulated spleen lymphocytes and Con A-stimulated thymus lymphocytes from each mouse strain. On the whole, MNU-produced SCE were lower in AKR and CBA spleens than in C57BL/6N x DBA/2J F1 spleens. In addition, MNU-induced SCE levels in thymus lymphocytes from all three strains of mice were, for the most part, similar. These results indicate that if differences in MNU-induced genotoxicity in AKR, CBA, and C57BL/6N x DBA/2J F1 thymus lymphocytes exist, these differences cannot be ascertained by use of the in vivo/in vitro SCE assay.