Oxygen radical-mediated reduction in basal and agonist-evoked NO release in isolated rat heart.
Oxygen free radicals (OFR) play a primary role in ischemia-reperfusion-mediated vascular dysfunction and this is paralleled by a loss of endothelial nitric oxide synthase (eNOS) activity. The authors tested whether a direct exposure to OFR may affect vascular relaxation by altering nitric oxide (NO) release. Effects of electrolysis(EL)-generated OFR on basal and agonist-evoked NO release were monitored in isolated rat hearts by oxyhemoglobin assay. Electrolysis-induced changes were compared with those obtained after 30 min perfusion with NOS and cyclooxygenase (COX) inhibitors NG-nitro-L-arginine methyl ester (L-NAME, 100 microM) and indomethacin (INDO, 1 m M). Electrolysis-generated hydroxyl radical (.OH) formed by.O2-and H2O2 via the Fenton reaction as revealed by Electron Paramagnetic Resonance (EPR). After EL, basal NO release declined by 60% and coronary perfusion pressure (CPP) increased by approximately 70%. L-NAME/INDO perfusion similarly lowered NO release (-63%) but increased CPP less than EL (56+/-3%P<0.03 v post-EL). In presence of excess substrates and cofactors eNOS activity was not affected by EL. Both acetylcholine (ACh; 1 microM) and bradykinin (BK; 10 n M) had minimal effect in reversing EL-induced vasoconstriction, whereas both partially reversed L -NAME/INDO-mediated constriction. Sodium nitroprusside (SNP, 1 microM) completely reversed L-NAME/INDO constriction and partly countered that after EL (-38+/-2.5, P<0.001). Acetylcholine-evoked NO release was nearly abolished by both treatments whereas BK still elicited partial NO release after eNOS/cyclooxygenase inhibition (P<0.001) but not after EL. In conclusion, OFR severely impair NO-mediated coronary vasorelaxation affecting both basal and agonist-evoked NO release but not eNOS activity. However, EL also significantly blunts NOS/COX-independent vasodilation suggesting alteration of other vasodilatative pathways.
Paolocci
N
N
Division of Cardiology, The Johns Hopkins Medical Institutions,Baltimore, MD 21287-6568, USA. npaolocc@mail.jhmi.edu
Biondi
R
R
Bettini
M
M
Lee
C I
CI
Berlowitz
C O
CO
Rossi
R
R
Xia
Y
Y
Ambrosio
G
G
L'Abbate
A
A
Kass
D A
DA
Zweier
J L
JL
D000109:Acetylcholine / Q000378:metabolism; D000818:Animals; D001920:Bradykinin / Q000378:metabolism; D016861:Cyclooxygenase Inhibitors / Q000494:pharmacology; D004572:Electrolysis; D006321:Heart / Q000187:drug effects / Q000502:physiology*; D017665:Hydroxyl Radical / Q000378:metabolism*; D066298:In Vitro Techniques; D007213:Indomethacin / Q000494:pharmacology; D008297:Male; D009206:Myocardium / Q000378:metabolism*; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009569:Nitric Oxide / Q000378:metabolism*; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors; D009599:Nitroprusside / Q000378:metabolism; D010084:Oxidation-Reduction; D051381:Rats; D017207:Rats, Sprague-Dawley; D013481:Superoxides / Q000378:metabolism*
D016861:Cyclooxygenase Inhibitors; D013481:Superoxides; D009599:Nitroprusside; D009569:Nitric Oxide; D017665:Hydroxyl Radical; D019001:Nitric Oxide Synthase; D000109:Acetylcholine; D001920:Bradykinin; D019331:NG-Nitroarginine Methyl Ester; D007213:Indomethacin