A study of the effect of chronic applications of nitrogen mustard (HN2) on acute responses of mammalian skin to UVB irradiation in vivo.

The effect of chronic applications of HN2 on acute responses of DNA synthesis to UVB radiation was studied in Uscd strain hairless mouse skin in vivo. 0.1 mg of HN2 in 95% ethyl alcohol and the diluent were applied weekly to the backs of the mice for 69 wk. The mice were then exposed to 1.98 X 10(2) J/m2 of UVB energy and were sacrified 4 hours and 48 h post-irradiation. The effects on DNA synthesis were evaluated using TdRH3 as the radioactive tracer. The results of the study revealed that the chronic HN2 applications increased the number of basal cells in the DNA synthesis phase of the mitotic cycle. This was associated with acanthosis and cellular hypertrophy. 4 h post-irradiation there was the expected depression in DNA synthesis in both the HN2- and diluent-treated mice. In addition, 48 h post-irradiation the number of basal cells synthesizing DNA was accelerated in both the HN2- and diluent-treated mice. However, it was much more noticeable in the HN2-treated animals. Whether this increased activity is related to the additive carcinogenesis generated between UVB and HN2 remains to be determined.