Mitochondria (mito) are a major source of reactive oxygen species (ROS) during ischemia reperfusion (IR). IR damages mito respiratory complexes and increases mitochondrial ROS production. Ischemic preconditioning (IPC) protects myocardium from IR injury. It is unclear what the effect of IPC is on mito ROS generation. The purpose of this study was to evaluate the effect of IPC on mito ROS production and respiratory complex activity. Isolated rat hearts (n=6/group) were subjected to either CONTROL: 30 minutes (min) of equilibration (EQ), 30 min of ischemia (I), and 30 min of reperfusion (RP), or IPC: 10 min of EQ, preconditioning was then induced by two 5 min episodes of ischemia separated by 5 minutes of reperfusion, 30 min I, and 30 min of RP. Mitochondria were isolated at end EQ, at end I, and at end RP. Superoxide production by complexes I and III was assessed by electron paramagnetic resonance (EPR) spectroscopy using the spin trap 5,5-dimethylpyrroline N-oxide (DMPO). Respiratory complex I activity was measured by polarography. Data is expressed as mean±sem.

It has been demonstrated that ischemic postconditioning (PoC) protects myocardium from ischemia-reperfusion (IR) in vivo. There are conflicting reports on whether PoC occurs on the isolated crystalloid perfused rat heart. This lack of protection may be explained by the use of different PoC protocols and/or different gender susceptibility to IR. We investigated different PoC protocols in male and female isolated rat hearts and their effect on myocardial performance and infarct size after IR. Isolated rat hearts (n=6/group) were perfused on a Langendorff apparatus with Krebs-Henseleit buffer (37 °C) and subjected to either Control: 30 minutes (min) of equilibration (EQ), 30 min of global ischemia (I), and 120 min of reperfusion (RP) or PoC: 30 min EQ, 30 min I, and then PoC was induced by either A: six cycles of 10 seconds (s) RP and 10 s I (6c10s); B: three cycles of 10 s RP and 10 s I (3c10s); or C: two cycles of 10 s RP and 10 s I (2c10s); and then reperfusion was carried out to 120 min. Male rats were subjected to all three PoC protocols and female rats were subjected to only A. At the end of experiments, infarct size was measured by TTC staining. Developed pressure, heart rate, and coronary flow were measured throughout the experiment. Data is expressed as mean±sem.