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Reperfusion of the ischemic myocardium leads to a burst of reactive [O.sub.2] species (ROS), which is a primary determinant of postischemic myocardial dysfunction. We tested the hypothesis that early [O.sub.2] delivery and the cellular redox state modulate the initial myocardial ROS production at reperfusion. Isolated buffer-perfused rat hearts were loaded with the fluorophores dihydrofluorescein or Amplex red to detect intracellular and extracellular ROS formation using surface fluorometry at the left ventricular wall. Hearts were made globally ischemic for 20 rain and then reperfused with either 95% or 20% [O.sub.2]-saturated perfusate. The same protocol was repeated in hearts loaded with dihydrofluorescein and perfused with either 20 or 5 mM glucose-buffered solution to determine relative changes in NADH and FAD. Myocardial [O.sub.2] delivery during the first 5 min of reperfusion was 84.7 [+ or -] 4.2 ml [O.sub.2]/min with 20% [O.sub.2]-saturated buffer and 354.4 [+ or -] 22.8 ml [O.sub.2]/min with 95% [O.sub.2] (n - 8/group, P < 0.001). The fluorescein signal (intracellular ROS) was significantly increased in hearts reperfused with 95% [O.sub.2] compared with 20% [O.sub.2]. However, the resorufin signal (extracellular ROS) was significantly increased with 20% [O.sub.2] compared with 95% [O.sub.2] during reperfusion. Perfusion of hearts with 20 mM glucose reduced the NADH during ischemia (P < 0.001) and the ROS at reperfusion (P < 0.001) compared with 5.5 mM-perfused glucose hearts. In conclusion, initial [O.sub.2] delivery to the ischemic myocardium modulates a compartment-specific ROS response at reperfusion such that high [O.sub.2] delivery promotes intracellnlar ROS and low [O.sub.2] delivery promotes extracellular ROS. The redox state that develops during ischemia appears to be an important precursor fur reperfusion ROS production. ischemia; reoxygenation; oxygen radicals

Summary: Aim of study: Previous reports note an increase in both reactive oxygen species (ROS) and nitric oxide (e onset of myocardial reperfusion. We tested the hypothesis that inhibition of production at the time of reperfusion improves recovery of post-ischemic myocardial function. Methods and materials: Isolated rat hearts were perfused with temperature controlled (37.4°C) modified Krebs Henseleit buffer solution at 85mm Hg. Following 20min of global ischemia, hearts were reperfused for the first 10min with: (1) standard buffer (control), (2) buffer with a NOS inhibitor, N-nitro-l-arginine methyl ester (l-NAME), (3) buffer with superoxide dismutase (SOD) or (4) buffer with N-morpholinosydnonimine hydrochloride (SIN-1), a peroxynitrite generator. Tissue O2 and ontinuously measured with thin electrochemical probes embedded in the wall of the LV. ROS was measured with the spin trap 5,5-dimethyl-1-pyrroline N-oxide (DMPO) (40mM). LV contractile function was continuously monitored. Results: Recovery of LV contractile function was significantly improved in hearts initially reperfused with l-NAME and SOD and significantly depressed in hearts reperfused with SIN-1 compared with control (p <0.01, n =5–8 per group). DMPO-adduct during reperfusion (measure of ROS) was significantly decreased with SOD (p <0.001 versus l-NAME and Control, n =4 per group) and unchanged with l-NAME and SIN-1 compared with Control. With l-NAME, tissue 2 were significantly decreased, independent of coronary flow, during reperfusion compared with control and SIN-1. Conclusions: Inhibition of O2 − or time of reperfusion improves early reperfusion LV function and alters tissue oxygen tension. In contrast to pre-ischemic treatments, intervention to reduce peroxynitrite generation at the onset of reperfusion can effectively improve post-ischemic myocardial recovery. [Copyright &y& Elsevier]

Reperfusion of the ischemic myocardium leads to a burst of reactive O2 species (ROS), which is a primary determinant of postischemic myocardial dysfunction. We tested the hypothesis that early O2 delivery and the cellular redox state modulate the initial myocardial ROS production at reperfusion. Isolated buffer-perfused rat hearts were loaded with the fluorophores dihydrofluorescein or Amplex red to detect intracellular and extracellular ROS formation using surface fluorometry at the left ventricular wall. Hearts were made globally ischemic for 20 mm and then reperfused with either 95% or 20% O2-saturated perfusate. The same protocol was repeated in hearts loaded with dihydrofluorescein and perfused with either 20 or 5 mM glucose-buffered solution to deter- mine relative changes in NADH and FAD. Myocardial O2 delivery during the first 5 mm of reperfusion was 84.7 ± 4.2 ml O2/min with 20% O2-saturated buffer and 354.4 ± 22.8 ml O2/min with 95% O2 (n = 8/group, P<0.001). The fluorescein signal (intracellular ROS) was significantly increased in hearts reperfused with 95% O2 compared with 20% O2. However, the resorufin signal (extracellular ROS) was significantly increased with 20% O2 compared with 95% O2 during reperfusion. Perfusion of hearts with 20 mM glucose reduced the NADH during ischemia (P<0.001) and the ROS at reperfusion (P<0.001) compared with 5.5 mM-perfused glucose hearts. In conclusion, initial O2 delivery to the ischemic myocardium modulates a compartment-specific ROS response at reperfusion such that high O2 delivery promotes intracellular ROS and low O2 delivery promotes extracellular ROS. The redox state that develops during ischemia appears to be an important precursor for reperfusion ROS production. [ABSTRACT FROM AUTHOR]