Further studies on the action of ultraviolet light on vascular smooth muscle: effect of partial irreversible receptor blockade.

Isolated rabbit thoracic aorta which is pharmacologically contracted will relax when exposed to ultraviolet light. The relaxation is reversible in that the tension is restored when the light source is removed. The purpose of this investigation was to study further the phenomenon of photorelaxation on vascular smooth muscle. Restoration kinetics were examined for two cases: 1) norepinephrine alone 2) norepinephrine plus phenoxylbenzamine. The photo-induced relaxation in the presence of the irreversible blocker phenoxybenzamine produced a more rapid restoration than the photo-induced relaxation in strips contracted with norepinephrine alone. Angiotensin, which is not blocked by phenoxybenzamine, produced no change in the restoration characteristics of a perturbation on the angiotensin-induced contractions. Strips treated with glycerin, a process which removes storage sites for Ca++, are responsive to exogenous administration of Ca++ but demonstrate no photorelaxation. These results lend supportive evidence to the hypothesis that ultraviolet radiation interferes with the drug-receptor complex.