Ischemic preconditioning alters real-time measure of O2 radicals in intact hearts with ischemia and reperfusion

Abstract

Reactive oxygen species (ROS) are believed to be involved in triggering cardiac ischemic preconditioning (IPC). Decreased formation of ROS on reperfusion after prolonged ischemia may in part underlie protection by IPC. In heart models, these contentions have been based either on the effect of ROS scavengers to abrogate IPC-induced preservation or on a measurement of oxidation products on reperfusion. Using spectrophotofluorometry at the left ventricular wall and the fluorescent probe dihydroethidium (DHE), we measured intracellular ROS superoxide (O[Formula: see text]·) continuously in isolated guinea pig heart and tested the effect of IPC and the O[Formula: see text]· scavenger manganese(III) tetrakis (4-benzoic acid) porphyrin chloride (MnTBAP) on O[Formula: see text]· formation throughout the phases of preconditioning (PC), 30-min ischemia and 60-min reperfusion (I/R). IPC was evidenced by improved contractile function and reduced infarction; MnTBAP abrogated these effects. Brief PC pulses increased O[Formula: see text]· during the ischemic but not the reperfusion phase. O[Formula: see text]· increased by 35% within 1 min of ischemia, increased further to 95% after 20 min of ischemia, and decreased slowly on reperfusion. In the IPC group, O[Formula: see text]· was not elevated over 35% during index ischemia and was not increased at all on reperfusion; these effects were abrogated by MnTBAP. Our results directly demonstrate how intracellular ROS increase in intact hearts during IPC and I/R and clarify the role of ROS in triggering and mediating IPC.