Activation of guanylate cyclase in the guinea-pig trachea reduces contractile responses of the smooth muscle

Guinea-pig tracheal strips were used to investigate whether activation of guanylate cyclase in the trachea can reduce the contractile responses of the smooth muscle. Guanylate cyclase was activated by glyceryl trinitrate and a combination of sodium nitrite and ascorbic acid. These activators inhibited tracheal smooth muscle contractions produced by acetylcholine, histamine and electrical field stimulation. However, in the presence of methylene blue, a guanylate cyclase inhibitor, tracheal smooth muscle contractions were not inhibited by the activators. But, in the presence of propranolol, which blocked inhibition mediated by beta-adrenoceptor, both glyceryl trinitrate and the sodium nitrite/ascorbic acid combination were still capable of inhibiting tracheal smooth muscle contractions. Additionally, methylene blue inhibited tracheal smooth muscle relaxation that was electrically induced. These results suggest that the inhibitory action mediated by activated guanylate cyclase may be a mechanism for regulating tracheal smooth muscle contractile responses.