Effects of Short-Term L-Phe On Recombinant GCH1 Activity (In Vitro) and Systemic BH4 and Nitrite (In Vivo)
(A) GCH1 activity, determined by the production of the intermediate product reaction; dihydroneopterin triphosphate (DHNTP) at 340 nm of purified GCH1 (0.1 μmol·l−1) alone or in the presence of purified GFRP (1 μmol·l−1) and/or L-phe (1 mmol·l−1). The datasets shown represent the mean ± SEM of n = 4 (*p < 0.05). Quantitative measurement of temporal changes in plasma (B) BH4, and (C) nitrite, (D) BH2, and (E) biopterin following 100 mg·kg−1 L-phe challenge in WKY and SHR (given via oral gavage). The datasets shown represent the mean ± SEM of n = 6 animals per group per time point compared with baseline control (0 h) (*p < 0.05, ** p < 0.01, ***p < 0.001). (Exact p values are tabulated in the Supplemental Table 2). BH2 = dihydrobiopterin; BH4 = tetrahydrobiopterin; eNOS = endothelial nitric oxide synthase; GCH1 = GTP cyclohydrolase 1; L-Arg = l-arginine; L-phe = l-phenylalanine; SHR = spontaneously hypertensive rat(s); WKY = Wistar Kyoto rat(s).