DIFFERENTIAL-EFFECTS OF NITROVASODILATORS AND NITRIC-OXIDE ON PORCINETRACHEAL AND BRONCHIAL MUSCLE IN-VITRO

Nitrovasodilators and nitric oxide relax airway smooth muscle. The mec hanism by which nitrovasodilators are thought to act is by release of nitric oxide, but the importance of nitric oxide in nitrovasodilator-i nduced airway smooth muscle relaxation is unclear. The aim of this stu dy was to compare the relaxing effects of nitric oxide itself with tho se of nitrovasodilators in porcine tracheal muscle and intrapulmonary airways and to investigate the mechanisms involved. Strips of porcine tracheal smooth muscle, rings of bronchi, and strips of bronchi from t he same animal were suspended in organ chambers in modified Krebs Ring er solution (95% O-2-5% CO2, 37 degrees C). Tissues were contracted wi th carbachol, and concentration-response curves to nitric oxide, sodiu m nitroprusside, and SIN-1 (an active metabolite of molsidomine) were obtained. All tissues relaxed to sodium nitroprusside, SIN-1, and nitr ic oxide. The relaxation to nitric oxide but not to SIN-1 or sodium ni troprusside was inhibited by methylene blue. Tissues pretreated with m ethylene blue that failed to relax to nitric oxide were, however, rela xed by sodium nitroprusside. These results demonstrate that nitrovasod ilators relax airways by a mechanism other than by or in addition to t he release of nitric oxide.