Catalase, myoglobin and NO-synthase are heme proteins. Catalase is capable of producing NO from azide and hydroxylamine (Ignarro LJ, FASEB J 1989; 3:31-36). Heme is the center of catalyzing the production of NO. Thus, we investigated the mode of vasorelaxation induced by azide and nitrite in the endothelium-denuded aorta of guinea pig or rat. Both agents elicited a rapid relaxation of the aorta in a concentration dependent manner: EC50 values for azide and nitrite were 0.1 microM and 0.1 mM, respectively. These relaxation responses were inhibited by the presence of methylene blue, but not by NO-arginine or L-NMMA. Azide rapidly raised the cGMP content of the muscle, which seemed to precede the relaxation response. The catalase activity of the aorta was inhibited by azide and hydroxylamine with the similar IC50 values to EC50 values for relaxation. Myoglobin was found in the vessel tissue by the immunohistological method. Using a NO-sensitive electrode, the NO production from aortas was detected after addition of azide and nitrite. The NO production from nitrite was shown to precede the oxidation of heme moiety of oxymyoglobin. These results suggest that catalase as well as myoglobin, heme proteins, can be the cellular target for pharmacological agents to produce NO leading to vasorelaxation.
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