Tetrahydrobiopterin alters superoxide and nitric oxide release in prehypertensive rats

J Clin Invest. 1998 Apr 1;101(7):1530-7. doi: 10.1172/JCI650.

Abstract

Constitutive nitric oxide synthase (cNOS) with insufficient cofactor (6R)-5,6,7,8-tetrahydrobiopterin (H4B) may generate damaging superoxide (O2-). This study was designed to determine whether cNOS-dependent generation of O2- occurs in spontaneously hypertensive rats (SHR) before the onset of hypertension. Aortas from 4-wk-old SHR and Wistar-Kyoto rats were used. cNOS was stimulated by calcium ionophore A23187. In situ measurements of nitric oxide and hydrogen peroxide by electrochemical sensors and O2- production by chemiluminescence method were performed. Isometric tension was continuously recorded. H4B by high performance liquid chromatography and [3H]citrulline assay were determined in homogenized tissue. The A23187-stimulated production of O2- and its superoxide dismutase product hydrogen peroxide were significantly higher, whereas nitric oxide release was reduced in SHR aortas, with opposite results in the presence of exogenous H4B. Furthermore, NG-monomethyl-L-arginine inhibited the generation of cNOS-dependent O2- by approximately 70%. Natural H4B levels were similar in both strains; however, equivalent cNOS activity required additional H4B in SHR. The endothelium-dependent relaxations to A23187 were significantly inhibited by catalase, and enhanced by superoxide dismutase, only in SHR; however, these enzymes had no effect in the presence of H4B. Thus, dysfunctional cNOS may be a source of O2- in prehypertensive SHR and contribute to the development of hypertension and its vascular complications.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Aorta / metabolism*
  • Biopterin / analogs & derivatives*
  • Biopterin / pharmacology
  • Calcimycin / pharmacology
  • Dose-Response Relationship, Drug
  • Endothelium, Vascular / physiology
  • Hydrogen Peroxide / metabolism
  • Hypertension / metabolism*
  • In Vitro Techniques
  • Ionophores / pharmacology
  • Nitric Oxide / metabolism
  • Nitric Oxide Synthase / physiology*
  • Nitroprusside / pharmacology
  • Rats
  • Rats, Inbred SHR
  • Rats, Inbred WKY
  • Superoxides / metabolism
  • Vasomotor System / drug effects

Substances

  • Ionophores
  • Superoxides
  • Nitroprusside
  • Biopterin
  • Nitric Oxide
  • Calcimycin
  • Hydrogen Peroxide
  • Nitric Oxide Synthase
  • sapropterin