THE ROLES OF REACTIVE OXYGEN SPECIES AND ENDOGENOUS OPIOID-PEPTIDES IN ISCHEMIA-INDUCED ARRHYTHMIA OF ISOLATED RAT HEARTS

Although the formation of oxygen-derived free radicals (or reactive ox ygen species; ROS) and the release of endogenous opioid peptides (EOP) have been independently reported to be the major arrhythmogenic facto rs in ischemic hearts, possible relations between these two factors ha ve seldom been investigated. Thus, we studied whether the ROS and EOP were related in the progression of ischemia-induced arrhythmias. Isola ted rat hearts perfused in the Langendorff mode were treated with dyno rphin A1-13 (kappa EOP receptor agonist), and/or allopurinol (xanthine oxidase inhibitor), before the onset of ischemia induced by ligating the left coronary arteries. Ischemic period lasted for 30 min, during which cardiac rhythms were recorded. At the end of ischemia, hearts we re analyzed for the glutathione and ascorbate levels. Allopurinol (100 nmoles/heart) was effective in reducing the severity of arrhythmia (a rrhythmia score: Mean +/- SEM 3.00 +/- 0.80 for allopurinol, 5.75 +/- 0.41 for placebo, p < 0.01), while dynorphin (10 mu g/heart) potentiat ed the arrhythmia (6.71 +/- 0.52, p < 0.05 vs. placebo). Coadministrat ion of allopurinol and dynorphin was capable of reducing arrhythmia (5 .57 +/- 0.65) when compared with the administration of dynorphin alone (6.71 +/- 0.52, p < 0.05). Tissue oxidative stress was evaluated by t he concentrations of glutathione (GSH) and ascorbate. Allopurinol did not significantly elevate tissue GSH concentrations (1.46 +/- 0.05 mu moles/g wet wt) in ischemic hearts, while dynorphin alone significantl y decreased the GSH concentrations (0.96 +/- 0.08, p < 0.05) when comp ared with the placebo (1.32 +/- 0.03). The dynorphin-induced GSH decre ase cannot be reversed by coadministration with allopurinol (0.90 +/- 0.104). Allopurinol significantly elevated tissue ascorbate levels (0. 16 +/- 0.01) when compared with placebo (0.10 +/- 0.01,p < 0.05). Inte restingly, dynorphin alone also elevated the tissue ascorbate concentr ations (0.16 +/- 0.02). Coadministration of allopurinol and dynorphin further spiked the ascorbate levels (0.28 +/- 0.05, p < 0.01). In conc lusion, the results suggested that ischemia-induced arrhythmia mechani sms might involve the formation of superoxide and other ROS, which wer e probably generated from the release of EOP (or EOP/EOP receptor inte ractions). Superoxide, the formation of which can be inhibited by allo purinol that exerted antiarrhythmic effect, was probably scavenged by ascorbate in myocardial ischemia. The ROS resulting from EOP/EOP recep tor interactions were probably scavenged by glutathione system. Elevat ed ascorbate levels in dynorphin-treated hearts might result from the compensatory synthesis induced by decreased glutathione levels.