Differential effects of SOD on relaxation stimulated by SNOoxyHb, SNOmetHb, and GSNO. Vessels were precontracted and tension was measured as described in “Materials and methods.” Upon reaching a basal contractile tone, SOD (100 U/mL) or PBS vehicle control was added, followed by GSH (100 μM). Dose-dependent relaxation was then stimulated by addition of either SNOoxyHb (0-500 nM SNO), SNOmetHb (0-500 nM SNO), or GSNO (0-100 nM). The EC50s for relaxation with or without SOD were determined and the fold change in relaxation efficiency was calculated. SOD increased the relaxation efficiency of SNOmetHb and GSNO by approximately 3- to 4-fold but had no effect on SNOoxyHb-mediated responses. Values represent means ± SEM (n = 4-6) for SNOoxyHb and SNOmetHb. *P < .02 versus SNOoxyHb group and mean ± SEM (n = 3) for GSNO. **P < .001 versus SNOoxyHb group.
