Acute dorsal skin responses to UVB-irradiation in Wistar-derived hypotrichotic WBN/ILA-Ht rats

Acute responses of the dorsal skin to UVB-irradiation (10 kJ/m(2)) were compared between Wistar-derived hypotrichotic WBN/ILA-Ht rats and Wistar rats. In the epidermis of WBN/ILA-Ht rats, intracellular edema of keratinocytes: with or without nuclear shrinkage developed at 3 hours after irradiation mainly in the spinous layer. At 12 hours after irradiation, many sunburn cells characterized by eosinophilic cytoplasm and pyknotic nuclei were observed chiefly in the basal layer. Sunburn cells were mainly observed in the spinous and granular layers at 24 hours after irradiation, and they almost disappeared at 48 hours after irradiation when epidermal hyperplasia was detected. The nuclei of sunburn cells were strongly stained with TUNEL method, and they showed ultrastructural features characteristic for apoptotic nuclei. Moreover, the change in the percentage of TUNEL-positive keratinocytes corresponded well with that in the number of sunburn cells. In the dermis, inflammatory cell infiltration and edema with vascular dilatation were observed at 12 and 24 hours after irradiation. On the other hand, except for intracellular edema of keratinocytes mainly in the spinous layer, the intensity of skin lesions was greatly milder in Wistar rats. Especially, typical sunburn cells were only slightly observed in the basal layer at 24 hours after irradiation. Thus WBN/ILA-Ht rats were more sensitive to UVB-irradiation than Wistar rats, and WBN/ILA-Ht rats was considered to be a useful experimental animal in the field of photodermatology.