RESUMO
1. The hypothesis that the hydroxyl ion free radical, HO; derived from O2 plays a pivotal role in the development of reperfusion ventricular fibrillation was tested in 63 anesthetized mongrel dogs of either sex weighing 14 +/- 7 kg submitted to 90-min coronary occlusion followed by 60-min reperfusion. 2. OH. was blocked by the iron chelator deferoxamine (DF, 500 mg) and by dimethylthiourea (DMTU, 500 mg/kg), a HO. scavenger both given iv over 30 min before reperfusion. 3. The frequency of reperfusion ventricular fibrillation was similar in all animals, i.e., 7/27 (26 per cent ) control dogs, 7/23 (30 per cent ) DF-treated dogs and 3/13 (23 per cent ) DMTU-treated dogs. Arterial pressure, heart rate and double product were not significantly different among the three groups during occlusion or reperfusion. The hemodynamic variables were also similar among dogs that fibrillated and those that did not. Likewise, extent of ischemic areas and necrosis was similar among the three experimental groups, with the control values being 34 +/- 4 per cent and 14 +/- 5 per cent , respectively. 4. We conclude that OH. does not play a major role in the induction of reperfusion ventricular fibrillation in the anesthetized dog with ischemia/necrosis