DEMONSTRATION OF FREE-RADICAL GENERATION IN THE STUNNED MYOCARDIUM INTHE CONSCIOUS DOG AND IDENTIFICATION OF MAJOR DIFFERENCES BETWEEN CONSCIOUS AND OPEN-CHEST DOGS

Conscious dogs undergoing a 15-min coronary occlusion were given alpha -phenyl N-tert-butyl nitrone (PBN) and the local coronary venous plasm a was analyzed by electron paramagnetic resonance spectroscopy. A prol onged myocardial release of PBN radical adducts was observed, which ex hibited a burst in the initial minutes of reflow (peaking at 3 min) an d then abated but continued for 1-3 h after reperfusion. Computer simu lation revealed the presence of at least two PBN adducts (a(N) = 15.2 G and a(beta)H = 6.0 G; a(N) = 14.6 G and a(beta)H = 3.0 G), both cons istent with the trapping of secondary carbon-centered radicals. No app reciable PBN adduct production was observed when collateral flow excee ded 30-40% of nonischemic flow, indicating that a flow reduction of at least 60% is necessary to trigger free radical reactions. There was a direct relationship between the magnitude of PBN adduct production an d the severity of contractile dysfunction (r = 0.77), suggesting that the radicals generated upon reperfusion play a causal role in the subs equent stunning. The total release of PBN adducts after 3 h of reperfu sion following a 15-min coronary occlusion was found to be approximate ly five times greater in open-chest compared with conscious dogs; at t he same time, the recovery of wall thickening was markedly less in ope n-chest dogs. This study represents the first application of spin trap ping to a conscious animal model of myocardial ischemia. The results d emonstrate (a) that free radicals are generated in the stunned myocard ium in the absence of the artificial or abnormal conditions associated with previously used models (isolated hearts, open-chest preparations ), and (b) that both the severity of postischemic dysfunction and the magnitude of the attendant free radical production are greatly exagger ated in the open-chest dog, implying that previous conclusions derived from this model may not be applicable to conscious animals or to huma ns. This investigation also provides a method to measure free radicals in awake animals.