Low-intensity light induces vasorelaxation: a study for possible mechanism

To investigate the mechanism of light induced vasorelaxation, vascular tension change in normal buffer solution was compared with that in the buffer containing either the following drug: (1) guanylate cyclase inhibitor; (2) nitric oxide synthetase inhibitors and the optical isomers; and (3) vasodilating agent. The vasorelaxation caused by ultraviolet light irradiation was independent of the presence of an intact endothelium. It was inhibited by methyleneblue, but not influenced by either L-NMMA or D-NMMA. On the other hand, this vasorelaxation was enhanced by the agents containing nitro group (L-NAME, D-NAME) or sodium nitrite. These results show that the light activates guanylate cyclase, which results in the vasorelaxation. This activation was reinforced by the agents containing nitro group. We conclude that primary photochemical product, which is probably nitric oxide originated from photodissociation of nitro groups, may produce the vasorelaxation. The preliminary investigation suggests that ultraviolet irradiation may be benefit in the treatment for vasospasm.