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 microM and 100 microM 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 room light, or were exposed to ultraviolet light (365 nm), for 30 min (24 degrees 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.