Tetrahydrobiopterin alters superoxide and nitric oxide release in prehypertensive rats

Constitutive nitric oxide synthase (cNOS) with insufficient cofactor (6R)-5,6,7,8-tetrahydrobiopterin (H(4)B) may generate damaging superoxide (O(2)(-)), This study was designed to determine whether cNOS-dependent generation of O(2)(-) 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 O(2)(-) production by chemiluminescence method were performed, Isometric tension was continuously recorded, H(4)B by high performance liquid chromatography and [(3)H]citrulline assay were determined in homogenized tissue, The A23187-stimulated production of O(2)(-) 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 H(4)B. Furthermore, N(G)-monomethyl-L-arginine inhibited the generation of cNOS-dependent O(2)(-) by similar to 70%. Natural H(4)B levels were similar in both strains; however, equivalent. cNOS activity required additional H(4)B 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 H(4)B. Thus, dysfunctional cNOS may be a source of O(2)(-) in prehypertensive SHR and contribute to the development of hypertension and its vascular complications.