Isolated perfused rat hearts release secondary free radicals during ischemia reperfusion injury: Cardiovascular effects of the spin trap alpha-phenylN-tert-butylnitrone

Free radicals produced during myocardial postischemic reperfusion are aggra vating factors for functional disturbances and cellular injury. The aim of our work was to investigate the significance of the secondary free radical release during non ischemic perfusion and post-ischemic reperfusion and to evaluate the cardiovascular effects of the spin trap used. For that purpose , isolated perfused rat hearts underwent 0, 20, 30 or 60 min of a total isc hemia, followed by 30 min of reperfusion. The spin trap: alpha -phenyl N-te rt-butylnitrone (PBN) was used (3 mM). Functional parameters were recorded and samples of coronary effluents were collected and analyzed using Electro n Paramagnetic Resonance (EPR) to identify and quantify the amount of spin adducts produced. During non ischemic perfusion, almost undetectable levels of free radical release were observed. Conversely, a large and long-lastin g (30 min) release of spin adducts was detected from the onset of reperfusi on. The free radical species were identified as alkyl and alkoxyl radicals with amounts reaching 40 times the pro-ischemic values. On the other hand, PBN showed a cardioprotective effect, allowing a significant reduction of r hythm disturbances and a better postischemic recovery for the hearts which were submitted to 20 min of ischemia. When the duration of ischemia increas ed, the protective effects of PBN disappeared and toxic effects became more important. Our results have therefore confirmed the antioxidant and protec tive properties of a spin trap agent such as PBN. Moreover, we demonstrated that the persistent post-ischemic dysfunction was associated with a sustai ned production and release of free radical species.