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This Article Full Text Full Text (PDF) All Versions of this Article: 291/4/H1988    most recent 00145.2006v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via ISI Web of Science (3) Citing Articles via Google Scholar Google Scholar Articles by Hink, J. Articles by Jansen, E. Search for Related Content PubMed PubMed Citation Articles by Hink, J. Articles by Jansen, E.

Vascular reactivity and endothelial NOS activity in rat thoracic aorta during and after hyperbaric oxygen exposure

¹Royal Danish Naval Diving School, The Danish Armed Forces, Departments of ²Medical Physiology and ³Medical Biochemistry and Genetics, The Panum Institute, University of Copenhagen, ⁶Hyperbaric Oxygen Treatment Unit, Department of Anaesthesia, The Centre of Head and Orthopaedics, Copenhagen University Hospital Rigshospitalet, Copenhagen, ⁵Department of Pharmacology, University of Aarhus, Aarhus, Denmark; and ⁴Department of Emergency Medicine, Institute for Environmental Medicine, University of Pennsylvania Medical Center, Philadelphia, Pennsylvania

Submitted 9 February 2006 ; accepted in final form 31 March 2006

Accumulating evidence suggests that hyperbaric oxygen (HBO) stimulates neuronal nitric oxide (NO) synthase (NOS) activity, but the influence on endothelial NOS (eNOS) activity and vascular NO bioavailability remains unclear. We used a bioassay employing rat aortic rings to evaluate vascular NO bioavailability. HBO exposure to 2.8 atm absolute (ATA) in vitro decreased ACh relaxation. This effect remained unchanged, despite treatment with SOD-polyethylene glycol and catalase-polyethylene glycol, suggesting that the reduction in endothelium-derived NO bioavailability was independent of superoxide production. In vitro HBO induced contraction of resting aortic rings with and without endothelium, and these contractions were reduced by the NOS inhibitor N-nitro-L-arginine. In addition, in vitro HBO attenuated the vascular contraction produced by norepinephrine, and this effect was reversed by N-nitro-L-arginine, but not by endothelial denudation. These findings indicate stimulation of extraendothelial NO production during HBO exposure. A radiochemical assay was used to assess NOS activity in rat aortic endothelial cells. Catalytic activity of eNOS in cell homogenates was not decreased by HBO, and in vivo HBO exposure to 2.8 ATA was without effect on eNOS activity and/or vascular NO bioavailability in vitro. We conclude that HBO reduces endothelium-derived NO bioavailability independent of superoxide production, and this effect seems to be unrelated to a decrease in eNOS catalytic activity. In addition, HBO increases the resting tone of rat aortic rings and attenuates the contractile response to norepinephrine by endothelium-independent mechanisms that involve extraendothelial NO production.

nitric oxide synthase; acetylcholine relaxation; autooxidation