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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

Division of Genetic Toxicology, National Center for Toxicological Research, Food and Drug Administration, Department of Health and Human Services, Jefferson, Arkansas 72079 [R. E. N., H. M. S., D. A. C.]; and Department of Pharmacology and Toxicology and Department of Biochemistry, University of Arkansas for Medical Sciences, Little Rock, Arkansas 72205 [D. A. C.]

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 lipopolysaccharidestimulated 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.

Received 3/10/89. Revised 5/11/89. Accepted 5/18/89.