NO synthase uncoupling in the kidney of Dahl S rats: role of dihydrobiopterin.
NO synthase (NOS) can paradoxically contribute to the production of reactive oxygen species when l-arginine or the cofactor R-tetrahydrobiopterin (BH(4)) becomes limited. The present study examined whether NOS contributes to superoxide production in kidneys of hypertensive Dahl salt-sensitive (SS) rats compared with an inbred consomic control strain (SS-13(BN)) and tested the hypothesis that elevated dihydrobiopterin (BH(2)) levels are importantly involved in this process. This was assessed by determining the effects of l-nitroarginine methyl ester (l-NAME) inhibition of NOS on superoxide production and by comparing tissue concentrations of BH(4) and BH(2). A reverse-phase high-performance liquid chromatography method was applied for direct measurements of BH(4) and BH(2) using (S)-tetrahydrobiopterin as an internal standard. Superoxide concentrations were measured in vivo from medullary microdialysis fluid using dihydroethidine and in vitro using lucigenin. The results indicate the following: (1) that superoxide levels were elevated in the outer medulla of SS rats fed a 4% salt diet and could be inhibited by l-NAME. In contrast, l-NAME resulted in elevated superoxide production in consomic SS-13(BN) rats because of higher NOS activity; (2) SS rats showed a reduced ratio of BH(4)/BH(2) in the outer medulla that was driven by increased concentrations of BH(2); and (3) lower superoxide dismutase and catalase activities contributed to elevated reactive oxygen species in SS samples. Based on the shift of BH(4) to BH(2) and the observation of l-NAME inhibitable superoxide production, we conclude that NOS uncoupling occurs in the renal medulla of hypertensive SS rats fed a high-salt diet.
Taylor
Norman E
NE
Department of Physiology, Medical College of Wisconsin, Milwaukee, WI 53226, USA. ntaylor@mcw.edu
Maier
Kristopher G
KG
Roman
Richard J
RJ
Cowley
Allen W
AW
D000818:Animals; D001708:Biopterins / Q000031:analogs & derivatives* / Q000032:analysis / Q000378:metabolism; D004195:Disease Models, Animal; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006973:Hypertension / Q000503:physiopathology; D007668:Kidney / Q000378:metabolism*; D007679:Kidney Medulla / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D018384:Oxidative Stress / Q000502:physiology*; D051381:Rats; D020303:Rats, Inbred Dahl; D013481:Superoxides / Q000378:metabolism*
D004791:Enzyme Inhibitors; D013481:Superoxides; D001708:Biopterins; C017226:7,8-dihydrobiopterin; D019331:NG-Nitroarginine Methyl Ester