Effects of phenylalanine on GCH1 mRNA (A), BH4 (B), nitrite (C), NOS activity (D), and ROS (E) in the kidneys of Dahl SS rats fed a low salt or high salt diet. Each value represents the mean ± SEM, n = 6–8, * p<0.05 vs. LS group, # p<0.05 vs. HS group.