Tetrahydrobiopterin alters superoxide and nitric oxide release in prehypertensive rats.
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.
Cosentino
F
F
Cardiology and Cardiovascular Research, University Hospitals, 3010 Bern and 8091 Zürich, Switzerland.
Patton
S
S
d'Uscio
L V
LV
Werner
E R
ER
Werner-Felmayer
G
G
Moreau
P
P
Malinski
T
T
Lüscher
T F
TF
D000818:Animals; D001011:Aorta / Q000378:metabolism*; D001708:Biopterins / Q000031:analogs & derivatives* / Q000494:pharmacology; D000001:Calcimycin / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004730:Endothelium, Vascular / Q000502:physiology; D006861:Hydrogen Peroxide / Q000378:metabolism; D006973:Hypertension / Q000378:metabolism*; D066298:In Vitro Techniques; D007476:Ionophores / Q000494:pharmacology; D009569:Nitric Oxide / Q000378:metabolism; D019001:Nitric Oxide Synthase / Q000502:physiology*; D009599:Nitroprusside / Q000494:pharmacology; D051381:Rats; D011918:Rats, Inbred SHR; D011921:Rats, Inbred WKY; D013481:Superoxides / Q000378:metabolism; D014666:Vasomotor System / Q000187:drug effects
D007476:Ionophores; D013481:Superoxides; D009599:Nitroprusside; D001708:Biopterins; D009569:Nitric Oxide; D000001:Calcimycin; D006861:Hydrogen Peroxide; D019001:Nitric Oxide Synthase; C003402:sapropterin