Figure 2 - The effects of several treatments on papaverine-induced increases in flow (open bars) and arterial plasma ascorbyl radical levels (closed bars). A pairwise control papaverine injection was performed in each rabbit before starting the treatments; however, since blood flow and ascorbyl radical changes were similar for all treatment groups for this control condition, the results were pooled for simplification (Control; N = 25). Neither L-NMMA (N = 6) nor D-NMMA (N = 6) altered papaverine-induced flow changes, but they both completely abolished the corresponding ascorbyl radical increase. Excess L-arginine coinfusion with L-NMMA (L-arg + L-NMMA; N = 5) did not overcome the blockade in ascorbyl increase. L-arginine (L-arg; N = 3) alone diminished papaverine-induced flow changes (P<0.05 vs other treatments), but did not impair ascorbyl radical increases. Data with L-NAME were previously published (9) and are shown only for comparison. **P<0.001, and *P<0.05 vs baseline, respectively (ANOVA and Student-Newman-Keuls multiple range test). Data are reported as means SEM.