Effects of double UVB-irradiations with different intervals on the dorsal skin of wistar-derived hypotrichotic WBN/ILA-Ht rats.

The effects of double irradiations of UVB (10 kJ/m2) with different intervals (12, 24 and 48 hr) were examined on the dorsal skin of Wistar-derived hypotrichotic WBN/ILA-Ht rats as the first step for long-term repeated irradiation study. The dorsal skin responses to a single UVB-irradiation were similar to those previously reported by our research group (Exp Toxicol Pathol, in press). In the groups which were given the 2nd irradiation at 12 and 24 hr after the 1st one, erythema, epidermal damage and subsequent hyperplasia, intradermal inflammatory cell infiltration and edema developed earlier and were more prominent especially in 12 hr-group compared with a single irradiation. However, the sequence of sunburn cells, the most characteristic epidermal change, was not different from that after a single irradiation. On the other hand, the dorsal skin responses to the 2nd irradiation at 48 hr after the 1st one were almost similar to those observed in the single irradiation-group except for epidermal hyperplasia being more prominent in 48 hr-group. This suggests that the responsibility of the dorsal skin almost recovered at 48 hr after the 1st irradiation.