UVB-induced pigmentation in brown guinea pigs

Eight-week-old female brown guinea pigs were supplied by Central Laboratory Animal Inc. (Seoul, Korea). Animal experimental protocol was approved by the ethical committee of Kyung Hee University (no: KHU-12-04) and was carried out in accordance with the approved guidelines. Brown guinea pigs were kept in an air-conditioned room under a temperature 24 °C ± 1 and light/dark cycle at 12 h. After acclimation one week, brown guinea pigs were housed in individual cages. Guinea pigs were anesthetized using ketamine and rompun (4:1 ratio, 1 ml/kg) and five separate areas (1.5 cm × 1.5 cm) on the back of each animal were exposed to UVB radiation (six UVB lamps: TL 20W/12RS, Phillips). The total energy dose of UVB irradiation was 380 mJ/cm² per exposure. Five skin sites from three animals were exposed to the UVB irradiation three times a week for three consecutive weeks. MNQO was then applied topically to the UVB-induced areas once a day for five consecutive weeks. The vehicle (propylene glycol:ethanol:water = 5:3:2) was used as a control. Colorimeter (CR-300, Minolta, Japan) was applied once a week for five consecutive weeks to determine the L value (lightness). The difference of L value was measured: