Abstract:

Objective    To study effects of various dosages of targeted high-intensity UVB and 311nm narrow band UVB (NB-UVB) on hyperpigmentation and expression of αmelanocyte-stimulating hormone(α-MSH) in the skin of guinea pigs. Methods    Five isolated areas were selected on the skin of brownish guinea pigs, and treated with different dosages of targeted high-intensity UVB and NB-UVB. Hyperpigmentation was evaluated by visual assessment and Fontana-Masson staining, and expression of αMSH was determined by immunohistochemistry. Results    Hyperpigmentation scores and melanin contents among the 5 groups were significantly different(P<0.01). There was no statistically significant difference between the high dosage and low dosage groups of targeted high-intensity UVB(P>0.05). However, they were significantly higher in targeted high-intensity UVB groups than in NB-UVB groups (P<0.05), and significantly higher in the high dosage group than in the low dosage group of NB-UVB（P<0.05）. Immunohistochemical scores of α-MSH among the 5 groups were significantly different(P<0.01)， and they were significantly higher in targeted high-intensity UVB groups than in NB-UVB groups（P<0.01）. However, there was no statistically significant difference between the high dosage and low dosage groups of each wavelength (P>0.05). Conclusions    Targeted high-intensity UVB phototherapy is more effective than NB-UVB to induce experimental hyper-pigmentation. Each kindof ultraviolet light can up-regulate expression of α-MSH in the epidermis, and the effect of targeted high-intensity UVB is better than that of NB-UVB.

Key words: Ultraviolet; Guinea pigs; Keratinocytes; Hyperpigmentation;  α-Melanocyte-stimulating hormone