Regulation of intracellular xanthine oxidase by endothelial-derived
nitric oxide.
Cote, Claudia G., Feng-Sheng Yu, Javier J. Zulueta, Robert J. Vosatka,
and Paul M. Hassoun.
Pulmonary and Critical Care Division/Department of Medicine, New
England Medical Center/Tufts University School of Medicine, Boston,
Massachusetts
APStracts 3:0130L, 1996.
We have previously shown that nitric oxide (NO) donors, such as
nitrosoglutathione, inhibit endothelial cell (EC) xanthine
dehydrogenase/xanthine oxidase (XD/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., nitro _ L-arginine methyl esther,
L-NAME, and N-nitro L-arginine, LNNA, 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 hr of exposure, respectively. The
combination of hypoxia and L-NAME (300 [mu]M) treatment amounted at
48 hr to a 10-and 7.5-fold increase in XO and XO+XD activities
respectively, as compared to normoxic untreated cells. L-NAME also
prevented the decline in XD/XO activity that occurred in untreated EC
following hypoxia-reoxygenation. On the other hand, treatment with L
-arginine caused a dose-dependent decrease in XD/XO activity in
hypoxic EC as compared to 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 five days to a
hypoxic, hypobaric atmosphere (0.5 atm). Exposure to hypoxia produced
a significant increase in lung tissue XO activity as well as an
increase in the ratio of XO/XD. L-arginine supplementation in the
drinking water completely prevented the increase in lung XO and XO/XD
ratio in hypoxic rats and caused a significant decrease in these
values 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.
Received 8 February 1996; accepted in final form 10 July 1996.
APS Manuscript Number L42-5.
Article publication pending Am. J. Physiol. (Lung Cell. Mol.
Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 21 August 1996