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Figure 1 Forearm blood flow responses to a) acetylcholine (ACh) at baseline and after placebo; b) ACh at baseline and after L-arginine; c) nitroprusside (NP) at baseline and after placebo; d) nitroprusside at baseline and after L-arginine. Responses to NP decreased significantly (p < 0.01) after L-arginine compared with placebo by two-way analysis of variance. Those to ACh tended to decrease but the difference did not reach significance (p < 0.1).