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Figure 1 Effects of oral sapropterin hydrochloride, an active analogue of tetrahydrobiopterin, on flow-mediated (top) and GTN-induced (bottom) vasodilation in smokers and nonsmokers. Flow-mediated vasodilation of the brachial artery at baseline was significantly smaller in smokers (p = 0.0002). In smokers, sapropterin significantly augmented FMV (p < 0.0001 by post hoc analysis) but did not affect it in nonsmokers (smokers vs. nonsmokers, p = 0.001 for the interactions by ANOVA). Glyceryl trinitrate–induced vasodilation was not altered by sapropterin in smokers and nonsmokers.