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Brachial artery flow-mediated dilatation (FMD) (top panel) and endothelium-independent dilatation (bottom panel) in young sedentary (black bars) and older sedentary (white bars) and regularly exercising (grey bars) healthy men after acute oral placebo (baseline conditions) or tetrahydrobiopterin (BH4) supplementation. FMD values are normalized for the stimulus. Mean ± s.e.m. values are shown. *P < 0.001 versus young and older exercising men. †P < 0.01 versus placebo condition.
