The Effect of UVA and UVB on DNA Synthesis and Unscheduled DNA Synthesis in Mouse Skin

Abstract

The effects of ultraviolet light A (UVA) and ultraviolet light B (UVB) on DNA synthesis and unscheduled DNA synthesis (UDS) were studied in mouse skin by microautoradiography. The mice were exposed to 50mJ / em" UVB by fluorescent sunlamp or 50J / ern" UVA by metal halide mercury lamp. Time course studies were performed immediately, 6 hours, 24 hours, and 48 hours after UVA and UVB exposure. There was no decreased number of heavily labeled cells (HLC) representing DNA synthesis immediately after UVA exposure and up to 48 hours postirradiation. However, immediately after and at 6 hours after UVA irradiation there was an increased number of sparsely labeled cells (SLC) representing UDS. Recovery was noticed 24 hours after irradiation and it was maintained after 48 hours postirradiation. These results clearly demonstrate that UVA induces considerable DNA damage and repair. DNA synthesis decreased immediately and at 6 hours and at 24 hours after UVB exposure. It recovered at 48 hours after UVB exposure. UDS increased immediately and at 6 hours after UVB exposure. Repair synthesis was completed at 24 hours after UVB exposure.