Figure 1 - Characteristic electron paramagnetic resonance spectra of arterial plasma ascorbyl radical (hyperfine splitting constant, aH = 0.186 mT) and its change in response to a flow increase induced by intra-arterial papaverine (2 mg) in untreated control animals. The increase in ascorbyl signals was completely abolished in rabbits treated with L-NMMA and D-NMMA. Peak flow increases occurred at 15 s and returned to baseline levels by 120 s after papaverine injection. Data acquisition parameters were as follows: potency, 20 mW; frequency, 9.7 GHz; modulation amplitude, 0.1 mT; sweeping velocity 0.01 mT/s; time constant, 1000 ms.