EFFECTS OF INDOMETHACIN ON SUNBURN AND SUNTAN REACTIONS IN HAIRLESS DESCENDANTS OF MEXICAN-HAIRLESS DOGS

The inhibitory effects of topical indomethacin (IM)-treatment on sunbu rn and suntan reactions after ultraviolet (UV)-irradiation were invest igated in the dorsal skin of hairless descendants of Mexican hairless dogs. Skin color, plasma prostaglandin E-2 (PGE(2)) and histological f eatures were examined. At 1 day after UV-irradiation, the IM-untreated sites showed prominent erythema, while the IM-treated sites exhibited few visible erythematous reactions. From 4 days after UV-irradiation, both the IM-treated and -untreated sites began to develop skin pigmen tation. Assessment of skin color changes, using a colorimeter, reflect ed precisely the color changes in visual sunburn and suntan reactions. Plasma PGE(2) concentration began to increase from 2 hours after UV-i rradiation, reached the maximal values at 24 hours and recovered at 96 hours after UV-irradiation. Histologically, at 1 day after UV-irradia tion, the IM-untreated sites showed remarkable epidermal degeneration (thickening and sunburn cells) and moderate alteration in the dermis. On the other hand, the IM-treated sites showed only minor histological changes. At 4 days after UV-irradiation, deposition of melanin granul es was found in both the IM-treated and -untreated sites. At 7 days af ter UV-irradiation, pigmentation became more prominent in the stratum basale. These results revealed that UV-induced erythematous reactions of hairless dogs were closely related to the action of PGE(2). Visuall y and histologically, topical IM-treatment had apparent inhibitory eff ects on erythematous reactions, while this agent showed no protective effects on epidermal pigmentation after UV-irradiation.