Involvement of nitric oxide in UVB-induced pigmentation in guinea pig skin

Ultraviolet (UV) B irradiation evolves erythema and delayed pigmentation in skin, where a variety of toxic and modulating events are known to be invol ved. Nitric oxide (NO) is generated from L-arginine buy NO synthases (NOS), Production of NO is enhanced in response to UVB-stimulation and has an imp ortant role in the development of erythema, NO has recently been demonstrat ed as a melanogen which stimulates melanocytes in vitro, however, no known in vivo data has been reported to support this finding. In this study, we i nvestigated the contribution of NO with UV-induced pigmentation in an anima l model using an NOS inhibitor. UVB-induced erythema in guinea pig skin was reduced when an NOS inhibit or, L-NAME (N-nitro-L-arginine methylester hyd rochloride), was topically applied to the skin daily beginning 3 days befor e UVB-irradiation. Delayed pigmentation and an increased number of DOPA-pos itive melanocytes in the skin were markedly suppressed by sequential daily treatment with L-NAME. Furthermore, melanin content 13 days after UVB-irrad iation was significantly lower in skin treated with NAME than in the contro ls. In contrast, D-NAME (N-nitro-D-arginine methylester hydrochloride), an ineffective isomer of L-NAME, demonstrated no effect on these UV-induced sk in responses. These results suggest that NO production may contribute to th e regulation of UVB-induced pigmentation.