Spin-trapping evidence that graded myocardial ischemia alters post-ischemic superoxide production

The spin trapping agent 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) was used to investigate oxy-radical production in post-ischemic rat hearts previously exposed to 20, 30, or 40 minutes of global ischemia. A hydroxyl spin adduct (DMPO-OH) was identified in coronary effluent during the initial seconds of reperfusion by Electron Spin Resonance (ESR) Spectroscopy. The intensity of the ESR signal in post-ischemic effluent increased as ischemic duration was prolonged; however, regardless of the duration of ischemia, maximal spin adduct detection occurred 3 minutes after initiation of reperfusion. Superoxide dismutase inhibited the formation of DMPO-OH, suggesting that superoxide anion was initially generated and is the principle source for the production on the hydroxyl adduct. Our investigations indicate that superoxide anion is produced during the early moments of reperfusion and that its production in the post-ischemic heart is related to the severity of ischemia.