This study was aimed at defining the varying responses of porcine coronary artery(PCA) to various wavelengths of ultraviolet irradiation, and at relating them to the changes in cyclic GMP contents.

The ring preparations of PCA with intact or removed endothelium were irradiated with the ultraviolet or visible light of wavelengths(240-520mm) from xenon lamp of a spectrofluorometer, and the changes in vascular tension were recorder on polygraph. For cyclic GMP assay, rat thoracic aorta was frozen after irradiation and homogenated. The supernatant was extracted with water-saturated ether and the cyclic GMP contents were measured with radioimmunoassay.

Ultraviolet irradiation relaxed the preparations(UVR-relaxation) in resting state and those precontracted by prostaglandin F_2α, the maximal relaxation occurring at 410nm, and the magnitude depending on the duration of irradiation. The UVR-relaxation was not affected by removing the endothelium, while it was markedly potentiated by pretreatment with Bay K 8644. The Bay K 8644-induced potentiation of UVR-relaxation was abolished by hemoglobin and slightly reduced by wrapping the rings with aluminum foil. Cyclic GMP contents in the increase was markedly potentiated by pretreatment with Bay K 8644.

The observations suggest that UVR-relaxation in procine coronary artery is caused by activating the nitric oxide-cyclic GMP system, which is most sensitively activated by UVR of 410nm and that its potentiation induced by Bay K 8644 may be related nitrous substance released from the agent upon UVR.