Abstract 2083: NO/ROS Interaction and Early Recovery of Post-Ischemic Heart Function
Nitric oxide (NO) is generally thought to be cardioprotective during reperfusion. As increased levels of both NO and reactive oxygen species (ROS) have been observed at the onset of reperfusion, we hypothesized that recovery of LV function may be in part determined by the interaction of NO and ROS at reperfusion. To test this hypothesis we measured early recovery of LV function after blocking either ROS or NO at the onset of reperfusion.
Methods: Isolated rat hearts were perfused with temperature controlled (37.4° C) Krebs Henseleit buffer at 85 mm Hg. Following 20 min of global ischemia, hearts were initially reperfused with 1) standard oxygenated buffer (control), 2) buffer with a NOS inhibitor, N-nitro-L-arginine methyl ester (L-NAME) or 3) buffer with superoxide dismutase (SOD). Tissue O2 and NO were continuously measured with thin electrochemical probes embedded in the wall of the LV. The spin trap 5,5-dimethyl-1-pyrroline N-oxide (DMPO) (40mM) was infused during the first 10 min of reperfusion to measure ROS. DMPO-free radical adduct concentration was quantitated in the effluent using electron paramagnetic resonance methods. LV contractile function was determined by a balloon placed in the LV attached to a transducer.
Results: Recovery of LV contractile function was significantly higher in hearts initially reperfused with L-NAME (rate pressure product, dP/dtmax and developed pressure) and SOD (dP/dtmax) compared with control (p<0.01 with ANOVA, n=6 – 8/group). DMPO-adduct during reperfusion (measure of ROS) was significantly decreased with SOD and unchanged with L-NAME compared with Control (p<0.001 vs. L-NAME and Control with ANOVA, n=4/group). With L-NAME, tissue NO, coronary flow, and tissue PO2 were significantly decreased during reperfusion in contrast to SOD, in which NO and coronary flow were significantly increased compared with control.
Conclusion: In the initial reperfused heart, both SOD and L-NAME significantly improve early reperfusion LV function despite differential effects on reperfusion [ROS] and [NO]. As a reduction in either NO or ROS at reperfusion limits downstream peroxynitrite formation, these findings lend additional support for peroxynitrite as an important determinant of early recovery of post ischemic LV function.