Sister chromatid exchange distributions in rabbit lymphocytes treated with streptonigrin

Streptonigrin (NSC‐45383), a direct‐acting clastogen which induces SCEs in vivo and chromosome aberrations both in vivo and in vitro, was evaluated for SCE induction in both G0 and stimulated rabbit lymphocytes. Determinations were made for 16 cultures from seven female rabbits. These included controls as well as cells exposed to 90 μg/kg in vivo, cells pulse‐treated with 50 ng/ml in vitro, and a culture continuously exposed to 5 ng/ml in vitro. For all cultures the SCE/ cell frequency was determined from 20 complete (44 chromosome) metaphases and, in selected cultures, SCEs on individual chromosomes (880 per culture from 20 cells) were enumerated to determine SCE/chromosome frequency and the chromosomal distribution of SCEs. Analysis of variance and least significant difference tests of the √x transformed SCE/cell data show that cells exposed to Streptonigrin while dividing have significantly higher (P