Dose response, wavelength dependence, and time course of ultraviolet radiation-induced unscheduled DNA synthesis in mouse skin in vivo.

A new method for autoradiographic measurement of unscheduled DNA synthesis (UDS) in the skin in vivo after treatment with ultraviolet light (UV) was developed. The skin of the back of ICR mice was shaved and exposed to short-wave UV (254 nm) or UVAB (sunlamp, 270 to 440 nm, predominant emission at 312 nm) at various doses. Immediately after irradiation, an isotonic aqueous solution of [methyl-3H]thymidine was injected s.c. into a portion of the skin clamped off with ring-shaped forceps. By this method, dose-dependent UDS was clearly demonstrated as silver grains on various types of cells in the skin in response to 254 nm UV or sunlamp UV. However, the energy values at the two wavelengths required to induce the same UDS level differed by 1 order of magnitude. These findings suggested that this system should be useful for quantitative analysis of UV-induced DNA repair in individual cells of the skin in vivo. By this method, the wavelength difference in transmissibility was studied. Autoradiographic results clearly showed that sunlamp UV could reach deeper sites in the skin than did 254 nm UV. A time course study indicated that UDS was almost complete by 48 hr after 254 nm UV but still persisted at 48 hr after sunlamp UV. These results, together with the differences in transmissibility, support higher tumorigenic activity of sunlamp UV than of 254 nm UV to experimental animals.