Effects of indomethacin on sunburn and suntan reactions in hairless descendants of Mexican hairless dogs

Abstract

The inhibitory effects of topical indomethacin (1M)-treatment on sunburn and suntan reactions after ultraviolet (UV)-irradiation were investigated in the dorsal skin of hairless descendants of Mexican hairless dogs. Skin color, plasma prostaglandin E2 (PGE2) and histological features 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 pigmentation. Assessment of skin color changes, using a colorimeter, reflected precisely the color changes in visual sunburn and suntan reactions. Plasma PGE2 concentration began to increase from 2 hours after UV-irradiation, reached the maximal values at 24 hours and recovered at 96 hours after UVirradiation. Histologically, at 1 day after UV-irradiation, 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 granules was found in both the IM-treated and -untreated sites. At 7 days after 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 PGE2. Visually and histologically, topical IMtreatment had apparent inhibitory effects on erythematous reactions, while this agent showed no protective effects on epidermal pigmentation after UV-irradiation.