Phenylalanine improves dilation and blood pressure in GTP cyclohydrolase inhibition-induced hypertensive rats

Brett M. Mitchell, Anne M. Dorrance, R. Clinton Webb

Research output: Contribution to journalArticlepeer-review

25 Scopus citations


GTP cyclohydrolase (GTPCH), the rate-limiting enzyme in the production of the nitric oxide synthase cofactor tetrahydrobiopterin (BH4), is partly regulated by the GTPCH feedback regulatory protein (GFRP). GFRP can inhibit GTPCH by end-product negative feedback, and L-phenylalanine (L-Phe) reverses this inhibition and increases BH4 biosynthesis in vitro. We hypothesized that L-Phe would increase endothelium-dependent relaxation and decrease blood pressure in rats made hypertensive by GTPCH inhibition. Diamino-hydroxy-pyrimidine (DAHP, 10 mmol/L), a known inhibitor of GTPCH, was given with or without L-Phe or D-Phe (2 mmol/L) in the drinking water of rats for 3 days and blood pressure was measured via tail-cuff. Endothelium-intact aortic segments were hung in organ chambers for measurement of isometric force generation. Systolic blood pressure was increased significantly in DAHP-treated rats compared with controls. The addition of L-Phe attenuated the hypertensive effect, whereas D-Phe had no effect. Acetylcholine- and A23187-induced relaxation was decreased in aortas from DAHP-treated rats compared with controls, but was restored in aortas from DAHP+L-Phe-treated rats. Following NOS inhibition, sensitivity to sodium nitroprusside was increased in aortas from DAHP-treated rats, but restored in DAHP+L-Phe-treated rats. These results suggest that L-Phe can reverse GTPCH inhibition in vivo leading to increased vasodilation and decreased blood pressure.

Original languageEnglish (US)
Pages (from-to)758-763
Number of pages6
JournalJournal of Cardiovascular Pharmacology
Issue number6
StatePublished - Jun 2004


  • Experimental
  • GTP cyclohydrolase 1
  • GTP cyclohydrolase feedback regulatory protein
  • Hypertension
  • Nitric oxide synthase
  • Phenylalanine
  • Tetrahydrobiopterin

ASJC Scopus subject areas

  • Pharmacology
  • Cardiology and Cardiovascular Medicine


Dive into the research topics of 'Phenylalanine improves dilation and blood pressure in GTP cyclohydrolase inhibition-induced hypertensive rats'. Together they form a unique fingerprint.

Cite this