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Hyperoxia reduces basal release of nitric oxide and contracts porcine coronary arteries
Author(s) -
Pasgaard T.,
Stankevicius E.,
Jørgensen M. M.,
Østergaard L.,
Simonsen U.,
Frøbert O.
Publication year - 2007
Publication title -
acta physiologica
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.591
H-Index - 116
eISSN - 1748-1716
pISSN - 1748-1708
DOI - 10.1111/j.1748-1716.2007.01745.x
Subject(s) - hyperoxia , vasoconstriction , contraction (grammar) , enos , medicine , vasodilation , nitric oxide , endothelium , endocrinology , phosphorylation , nitric oxide synthase , chemistry , anesthesia , cardiology , biochemistry , lung
Aim: The purpose of the present study was to investigate whether changes in nitric oxide (NO) concentration is involved in hyperoxia‐induced vasoconstriction in porcine conduit coronary arteries. Methods: The effect of hyperoxia on NO release and vasoconstriction was evaluated by tension recording, microsensor measurements, and immunoblotting in porcine conduit coronary arteries contracted with U46619 or 5‐hydroxytryptamine. Results: In endothelium‐intact segments exchanging 20% O 2 , 5% CO 2 , 75% N 2 (normoxia) for 95% O 2 , 5% CO 2 (hyperoxia) increased contraction. In segments without endothelium hyperoxia‐evoked contraction was abolished, but restored by an encircling donor segment with endothelium. An inhibitor of NOS, asymmetric dimethylarginine (ADMA, 300 μ m ), reduced hyperoxic contraction and basal NO concentration by, respectively, 38 ± 12% and 46 ± 3% ( P < 0.05, n = 9). A NO donor, S ‐nitroso‐ N ‐acetylpenicillamine (SNAP), increased NO concentration and evoked relaxation to the same levels in normoxic and hyperoxic conditions. β‐actin and endothelial NO synthase (eNOS) protein expression was similar in normoxic and hyperoxic arterial segments. Phosphorylation of eNOS was unaltered in normoxia vs. hyperoxia, but phosphorylation of eNOS‐Ser 1177 was increased and phosphorylation of eNOS‐Thr 495 decreased by U46619. Blockers of ATP‐sensitive, voltage‐dependent and calcium‐activated K + channels did not change hyperoxic contraction. However, high extracellular K + concentration or a second and third exposure to hyperoxia decreased contraction. Conclusion: The present study provides direct evidence that hyperoxia reduces basal release of NO leading to depletable endothelium‐dependent vasoconstriction in porcine coronary arteries independent of changes in eNOS phosphorylation.