The Photoactivated Relaxation of Smooth Muscle of Rabbit Aorta

Abstract

n B S T R n C T Smooth muscle of strips of rabbit aorta, placed in a state of active tonic contraction by addition of a stimulating drug, relaxes during exposure to light. The relaxation is reversible. The extent of relaxation produced by a standard exposure depends on the preexposure level of active contraction but not on the nature of the stimulating drug used to produce contraction. With strips brought to an intermediate level of contraction, the degree of relaxation (steady state levels) is a rectangular hyperbolic function of radiation intensity. The kinetics of the relaxation process during irradiation and the recovery process following irradiation are consistent with the hypothesis that the primary photoactivated material initiates a reaction or reactions leading to a product which inhibits some process involved in the production of active contraction. The photorelaxation does not require the presence of oxygen. It is potentiated by reducing the temperature of the aortic strip. The action spectrum of the photorelaxation shows relatively low effectiveness at wavelengths above 450 m#. The effectiveness increases markedly and progressively as the wavelength is lowered below 450 m#, reaching a peak at 310 m#. A deep trough occurs at 280 m#. However, both peak and trough probably result from internal filtering due to absorption by proteins in the aortic strip. It is surmised that if a correction could be made for this internal filtering, the action spectrum would rise continuously down to wavelengths at least as low as 250 m/z. Several years ago the finding was m a d e that contracted strips of rabbit thoracic aorta undergo relaxation when exposed to light of sufficient intensity. In two preliminary reports (Furchgott et al., 1955; Furchgott, 1955) it was pointed out that this photoactivated response differed from others previously reported for smooth muscle (Adler, 1919; A z u m a and Hill, 1926; Azuma, 1927; Supniewski, 1927;Blum, 1941) in the following respects: (a) it could be produced by visible a n d near ultraviolet radiation without the addition of a photosensitizing agent; (b) it occurred in the absence as well as in the presence of oxygen; (c) the response was a reversible relaxation 499

Comparison of the Effects of Ultraviolet Light and Purinergic Nerve Stimulation on the Guinea‐pig Taenia Coli

“…light at similar wavelengths (Furchgott et al, 1961;Ehrreich & Furchgott, 1968). Non-vascular smooth muscle was found to be much less sensitive to u.v.…”

“…) light (Furchgott, Ehrreich & Greenblatt, 1961;Furchgott, 1962). Non-vascular smooth muscle is much less sensitive to u.v.…”

Iron‐sulphur cluster nitrosyls, a novel class of nitric oxide generator: mechanism of vasodilator action on rat isolated tail artery

“…Light from an Argon ion laser (L; Spectra Physics Ltd., type 168-09) could be made to irradiate the artery directly, so as to induce photorelaxation of vascular smooth muscle (Furchgott et al, 1961 agonist-induced perfusion pressure= 101 ± 3.5mmHg).…”

Pharmacology and therapeutic role of inorganic nitrite and nitrate in vasodilatation

“…Thus, in addition to the bioactivation of nitrate to nitrite via oral commensal bacteria, another endogenous pool of nitrate (or a closely related NO species that can give rise to nitrite) appears to exist in human skin that may contribute to BP regulation in response to exposure of the body to UVA/sunlight. These studies built on earlier investigations on the effects of light on vascular tone of isolated rabbit aortic strips in organ baths (Furchgott et al, 1961), a phenomenon known as 'photorelaxation'. In those studies, addition of sodium nitrite to the organ bath potentiated lightinduced vasorelaxation in an endothelium-independent manner (Matsunaga & Furchgott, 1989).…”