Nitric oxide synthase (NOS) is known to mediate ultraviolet B (UVB)-induced skin inflammation However, there is still ambiguity as to which NOS isotype mediates the process in vivo. Furthermore, contradictory results have been reported on which cell types respond to UVB irradiation in vitro.

This study was performed to evaluate the change of inducible NOS (iNOS) expression in vivo as a result of UVB radiation on the skin of a rat.

To examine the time-course change in iNOS expression in the rat skin, the rats were exposed to 400 ml/cm² of UVB radiation, and skin samples were taken at various time intervals up to 48 h. iNOS expression on the skin of a rat was evaluated by both Western blot analysis and immunohistochemical staining.

From Western blot analysis, UVB irradiation induced inducible NOS (iNOS) expression in the epidermis at 12-48 h postirradiation with a peak expression at 24 h. Immunohistochemical staining revealed that UVB-induced iNOS expression was localized to the epidermis and infiltrating inflammatory cells in the upper dermis of the rat.

iNOS was induced by UVB irradiation on the skin of a rat, mainly in the epidermis. Therefore, iNOS is supposed to be one of the major mediators with regard to inducing an inflammatory response in UVB-irradiated rat skin in vivo.