Superoxide Dismutase Plus Catalase Therapy Delays neither Cell Death nor the Loss of the TTC Reaction in Experimental Myocardial Infarction in Dogs

Studies to test whether superoxide dismutase (SOD), with or without catalase, limits myocardial infarct size have produced conflicting results. Positive results following short periods of reperfusion vs negative results following longer periods of reperfusion could be explained if either: (1) myocytes, initially salvaged by SOD, are killed by continued production of free radicals after the administered SOD have been excreted, or (2) false positive results occur because SOD transiently preserves the TTC reaction, despite loss of cellular viability. To evaluate these two possibilities, we measured infarct size after 90 min of ischemia and 4 h of reperfusion in SOD + catalase treated and untreated dogs. Treated dogs received a 60 min intra-atrial infusion of SOD (15 000 U/kg) plus catalase (CAT) (55 000 U/kg) beginning 25 min before reperfusion. Infarct size was measured using triphenyl tetrazolium (TTC) macrochemistry and was compared with the extent of necrosis assessed semi-quantitatively by light microscopy. Mean infarct size was similar in the control and treated groups. In addition, there was a positive linear correlation (r = 0.95) between the extent of necrosis estimated by microscopy and that estimated by TTC inn both groups, and treatment did not alter the regression line. These current results were compared with results from the control dogs from our previous study (Richard et al. , 1988) in which 90 min of ischemia was followed by 4 days of reperfusion. TTC-based infarct size at 4 days of reperfusion was similar to that observed in both groups at 4 h. These data indicate that oxygen free radicals, accessible to intravascular SOD and catalase, are not a cause of myocyte death detectable by measurement of infarct size after 4 h of reperfusion. Moreover, neither an "early protection, delayed death" hypothesis nor a specific preservation of the TTC reaction explain the positive results of other studies. TTC macrochemistry provides reliable estimates of myocardial infarct size, provided that sufficient magnification is used to permit resolution of interdigitating peninsulas of viable and necrotic tissue.