Photochemical generation of nitric oxide from nitro-containing compounds: Possible relation to vascular photorelaxation phenomena

We examined the production of nitric oxide (NO) from various nitro-containing compounds (500 μM and 100 μM solutions in Krebs buffer, pH 7.4). Sealed vials containing solutions of NaNO₂, N-nitro-L-arginine 4-nitrophenol, BAY K 8644, or N-nitro-L-arginine methyl ester were stored in the dark, under normal roomlight, or were exposed to ultraviolet light (365 nm), for 30 min (24°C). NO was measured in the vial headspace after 30 min, using a sensitive assay previously established in our laboratory. Production of NO was found to be dependent on the intensity of light exposure for all compounds, and the highest degree of light-induced production of NO was found for NaNO₂ and BAY K 8644 solutions. Since NO is a relaxant of smooth muscle, these results help explain the increased sensitivity to relaxation by UV light of vascular and other types of smooth muscle in the presence of NaNO₂, BAY K 8644 and N-nitro-L-arginine, as observed by other investigators.