Laser Induced Tension Change in Rat Aortic Smooth Muscle:In Vitro Study

We reported that vascular ring of a rat thoracic aorta reproducibly showed either contraction or relaxation during irradiation with low power laser (wavelength=325nm, 351nm, 458nm, 514.5nm, 800nm). To study the thermal effect, the tension of vascular rings was observed isometrically with the same absorbed energy by Argon ion laser irradiation at each wavelength (351nm, 458nm, 514.5nm, 800nm). Furthermore, to investigate the mechanism of laser induced vasorelaxation, the tension changes in normal buffer were compared with those in the buffer containing the following drug: 1) guanylate cyclase inhibitor (10-5M methyleneblue); 2) nitric oxide synthetase inhibitor (10-4 ML-NMMA,10-4 ML-NAME); 3) the optical isomer of L-NAME (10-4 MD-NAME); 4) 10-4 MNaNO2Laser irradiation of the wavelength ranging from the ultraviolet to the short visible induced vasorelaxation. Otherwise, vasocontraction was caused by the irradiation at the long visible to the near-infrared. At each wavelength the vascular rings tended to contract with the higher absorbed energy. The vasorelaxation caused by ultraviolet laser irradiation (325nm) was inhibited by methyleneblue, and not influenced by L-NMMA. Moreover, the photovasorelaxation was enhanced by NO2 containing molecules ( L-NAME, D-NAME) or NaNO2.These results suggest that the photovaso contraction is due to the thermal effect of laser irradiation and the photovasorelaxation is due to the primary photochemical effect of the irradiation. We conclude that the primary photochemical effect may be ascribed to NO like substance generated by laser irradiation.