Inhibitory actions of hydroxocobalamin, cyanocobalamin, and folic acid on the ultraviolet light-induced relaxation of the frog upper oesophageal strip

The applications of ultraviolet (UV) light (336 nm) on the upper oesophagea l strips of frog elicited relaxant responses in the presence of NaNO2 (50 m u M). The tissues were mounted under the tension 0.5 g in an organ bath con taining Ringer solution, maintained at 25 degrees C and gassed with 100% O- 2. The responses were recorded on a kymograph via an isotonic lever. Antime galoblastic agents, including hydroxocobalamin (1, 10, and 100 mu M), cyano cobalamin (1, 10, 25, and 100 mu M), and folic acid (1, 10, 50, 100, and 20 0 mu M), significantly attenuated the relaxation response to UV light. Foli nic acid (1, 10, 25, and 100 mu M), however, enhanced the relaxation. Pyrog allol (50 mu M), hydroquinone(50 mu M), and diethyldithiocarbamic acid (8 m M) were found ineffective for attenuation, though FeSO4 (200, 400, and 500 mu M) and hemoglobin (50 mu M), respectively, exerted significant inhibitio n. L-arginine methylester (500 mu M) did not impair UV-induced relaxation. Based on these results, we concluded that a mechanism involving undefined a ction(s) of antimegaloblastic drugs may cause alterations in the UV light-i nduced relaxation of the tissue used.