NO- and NO₂-carrying molecules potentiate photorelaxation in rat trachea and aorta

Photorelaxation elicited by ultraviolet light (366 nm) was investigated on isolated rat thoracic aorta and trachealis. Rat tracheal smooth muscle but not aorta did not show UV-induced photorelaxation. Both streptozotocin, NO- carrying molecule and N^ω-nitro-L-arginine, NO₂-carrying molecule significantly enhanced photorelaxation, concentration-dependently, in rat trachealis and aorta. Methylene blue (10 μM) inhibited the potentiation action of streptozotocin and N^ω-nitro-L-arginine in both tissues. Superoxide dismutase (300 U/ml) enhanced streptozotocin- and N^ω-nitro-L- arginine-potentiated photorelaxation in rat trachealis, while pyrogallol (0.1 mM), a potent O² generating agent, inhibited streptozotocin-potentiated photorelaxation in trachealis. Streptozotocin was much more effective than N^ω-nitro-L-Arginine in potentiating of photorelaxation elicited by UV light in both tissues. From these findings, we conclude that streptozotocin and N^ω-nitro-L-arginine produce EDRF like labile substance(s) by UV irradiation.