Photo-induced adequate nitric oxide (PIANO)-mediated relaxation in isolated rabbit corpus cavernosum

1. We further investigated our earlier proposal that NO- and NO₂-carrying molecules potentiate photorelaxation using isolated rabbit corpus cavernosum. 2. Corporal smooth muscle, in the presence or absence of endothelium, relaxed only slightly upon u.v. light (366 nm) irradiation. But, NO- and/or NO₂-containing compounds such as streptozotocin and N^G-nitro-l-arginine methyl ester significantly (P < 0.01) enhanced photorelaxation in this tissue. In addition, N^G-nitro-d-arginine methyl ester, known to lack inhibitory action on NO synthase, showed concentration-dependent potentiation of the photorelaxation. 3. Oxygen radical generating system via xanthine + xanthine oxidase and guanylate cyclase inhibitor, methylene blue, significantly (P < 0.05) inhibited the streptozotocin-potentiated photorelaxation. 4. Nitrite was accumulated by photolysis of streptozotocin, N^G-nitro-l-arginine methyl ester and N^G-nitro-d-arginine methyl ester, in a concentration and exposure time-dependent manner. 5. These observations indicate that NO is a potent relaxant of rabbit corpus cavernosum and further support our hypothesis that NO is released by photolysis from NO- and NO₂-carrying molecules.