Effect of diethylstilbestrol on the frequencies of sister chromatid exchange in vitro and in vivo.

The influence of diethylstilbestrol (DES) on the SCE frequency was studied in various cell systems (V79, HTC, DON, WI-38, human lymphocytes) differing in their ability to metabolize the two promutagens benzo(a)pyrene and cyclophosphamide as well as after incubation with exogenous metabolic systems (S9 mix and peroxidase/H2O2) and in vivo on cells from the bone marrow of the Chinese hamster. DES concentrations from 10(-6) to 10(-4) M were tested. Slight SCE induction was observed only at the highest concentration (10(-4) M) of DES in human lymphocytes treated with DES for the entire culture period of 72 h and in DON cells. No increase of the SCE rate was determined in the other cell lines and in vivo. The combination with S9 mix or peroxidase/H2O2 also had no influence on the SCE frequency. These findings cast doubt on the assumption that DES is metabolized to a DNA-damaging compound subsequently leading to SCE induction. The positive findings in the SCE test are more likely to be products of an indirect and rather unspecific effect.