Oxygen radical-mediated reduction in basal and agonist-evoked NO release in isolated rat heart.

Abstract 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 N G -nitro- L -arginine methyl ester ( L -NAME, 100 μ M ) and indomethacin (INDO, 1 m M ). Electrolysis-generated hydroxyl radical ( . OH) formed by . O 2 − and H 2 O 2 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 ∼70%. L -NAME/INDO perfusion similarly lowered NO release (−63%) but increased CPP less than EL (56±3% P v post-EL). In presence of excess substrates and cofactors eNOS activity was not affected by EL. Both acetylcholine (ACh; 1 μ M ) and bradykinin (BK; 10 n M ) had minimal effect in reversing EL-induced vasocontriction, whereas both partially reversed L -NAME/INDO-mediated constriction. Sodium nitroprusside (SNP, 1 μ M ) completely reversed L -NAME/INDO constriction and partly countered that after EL (−38±2.5, P P