title: Regulation of intracellular xanthine oxidase by endothelial-derived nitric oxide.
abstract: We have previously shown that nitric oxide (NO) donors, such as nitrosoglutathione, inhibit endothelial cell (EC) xanthine dehydrogenase (XD)/xanthine oxidase (XO) activity. The purpose of this study was to assess whether endothelial-derived NO plays any role in the regulation of intracellular XD/XO. We exposed rat pulmonary microvascular EC to L-arginine (precursor of NO) or inhibitors of nitric oxide synthase (NOS), i.e., NG-nitro-L-arginine methyl esther (L-NAME) and NG-nitro-L-arginine, in conditions of normoxia, hypoxia, and hypoxia followed by reoxygenation. Hypoxia alone caused a 1.9- and a 6.6-fold increase in XO and a 5-fold increase in XO + XD activities after 24 and 48 h of exposure, respectively. The combination of hypoxia and L-NAME (300 microM) treatment amounted at 48 h to a 10- and 7.5-fold increase in XO and XO + XD activities, respectively, compared with normoxic untreated cells. L-NAME also prevented the decline in XD/XO activity that occurred in untreated EC after hypoxia-reoxygenation. On the other hand, treatment with L-arginine caused a dose-dependent decrease in XD/XO activity in hypoxic EC compared with cells provided with L-arginine-free medium. In separate experiments, we assessed the role of L-arginine supplementation on the in vivo regulation of lung XD/XO by exposing male adult Sprague-Dawley rats for a period of 5 days to a hypoxic hypobaric atmosphere (0.5 atm). Exposure to hypoxia produced a significant increase in lung tissue XO activity and an increase in the ratio of XO to XD. L-Arginine supplementation in the drinking water prevented the increase in lung XO and the XO-to-XD ratio in hypoxic rats and caused a significant decrease in XO and XD in rats exposed to normoxia. In conclusion, this study suggests that endogenous NO has a significant role in the regulation of XD/XO both in vitro and in vivo. By inhibiting XD/XO activity, NO may have a modulating effect in conditions of hypoxia and hypoxia-reoxygenation, where this enzyme is thought to be important.
authors.affiliation: Department of Medicine, New England Medical Center, Tufts University School of Medicine, Boston, Massachusetts 02111, USA.
authors.forename: C G
authors.initials: CG
authors.lastname: Cote
authors.forename: F S
authors.initials: FS
authors.lastname: Yu
authors.forename: J J
authors.initials: JJ
authors.lastname: Zulueta
authors.forename: R J
authors.initials: RJ
authors.lastname: Vosatka
authors.forename: P M
authors.initials: PM
authors.lastname: Hassoun
mesh_terms: D000818:Animals; D001120:Arginine / Q000494:pharmacology; D015687:Cell Hypoxia; D002478:Cells, Cultured; D004730:Endothelium, Vascular / Q000187:drug effects / Q000201:enzymology*; D007700:Kinetics; D008297:Male; D008833:Microcirculation; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D010100:Oxygen / Q000494:pharmacology; D011652:Pulmonary Circulation; D051381:Rats; D017207:Rats, Sprague-Dawley; D013997:Time Factors; D014968:Xanthine Dehydrogenase / Q000378:metabolism*; D014969:Xanthine Oxidase / Q000378:metabolism*
chemical_list: D001120:Arginine; D014968:Xanthine Dehydrogenase; D014969:Xanthine Oxidase; D010100:Oxygen; D019331:NG-Nitroarginine Methyl Ester