Ultraviolet-irradiated human endothelial cells elaborate nitric oxide that may evoke vasodilatory response

Human skin absorbs solar ultraviolet radiation which evokes vasodilation by a mechanism that is unknown. In this work, we show that ultraviolet (290-320 nm) irradiation of cultured human endothelial cells with doses (60 mJ/cm2) evoked nitric oxide (NO) release that was sustained for more than 60 min. In addition to augmenting NO, cyclic GMP production by human endothelial cells was also increased in a time-dependent manner. Ultraviolet stimulation of NO production was also observed with the enzyme NO synthase purified from the cytosol of human endothelial cells. These results indicate that ultraviolet radiation stimulates NO release, which stimulates cyclic GMP production by vascular smooth muscle, which results in a relaxation response.