Abstract
The activity of ultraviolet(UV)light to induce unscheduled DNA synthesis(UDS)was investigated in hairless mouse epidermis by means of an in vivo-in vitro assay using a liquid scintillation counting method. Groups of three to five 8-week-old female hairless mice were irradiated with UV-B or UV-A, then skin samples were taken and cultured individually in medium containing[3H]thymidine with or without hydroxyurea(HU)for 2 hr. DNA of the epidermis was extracted, and incorporation of[3H]thymidine and the DNA content were determined with a liquid scintillation counter and a fluorescence spectrophotometer, respectively. Induction of UDS was judged in terms of the UDS index[(the ratio of DNA synthesis in the presence of HU to that in its absence)×100]. UV-B increased the UDS index 1 hr after irradiation of 500 J / m2, which corresponds to approximately 1 minimal erythema dose or 1 minimal edema dose, and showed a dose-dependent increase up to 17-fold in the UDS index at irradiation doses of 500 to 2, 000 J / m2. In a time-coures study, UV-B also increased replicative DNA synthesis(RDS)48 hr after irradiation at 1, 000 J / m2. On the other hand, UV-A did not increase the UDS index at irradiation doses of 2×105 to 8×105 J / m2. These results show that induction of UDS by UV irradiation depends on wavelength, and an increase of RDS in the epidermis exposed to UV-B irradiation appears after induction of UDS.
