Characterization of exogenous hydroxyl radical effects on myocardial function, metabolism and ultrastructure.

EDTA-chelated ferrous chloride (Fe(2+)-EDTA) mixed with ascorbic acid (VC) was shown in vitro to produce 2,3-dihydroxybenzoic acid (2,3-DHBA), one of the hydroxyl radical (.OH) derivatives formed from reaction with 1 mM salicylic acid. The .OH generating system of Fe(2+)-EDTA (5, 25 and 50 microM) mixed with VC (50, 250 and 500 microM) was perfused for 15 min to the isolated rat hearts to characterize the effect of exogenous .OH on cardiac function, metabolism, and structure. A dose-effect relationship was observed between .OH dosage and ventricular dysfunction, increase in coronary flow, structural damage, decrease in ATP and increase in lipid peroxidation. Catalase (CAT, 500 U/ml) and deferoxamine (DFX, 10 mM) significantly (P < 0.05) reduced .OH formation in vitro, but superoxide dismutase (SOD, 100 U/ml) did not. When these agents were given to the heart perfused with 50 microM Fe(2+)-EDTA plus 500 microM VC, SOD failed to modify any myocardial alterations whereas CAT and DFX completely reversed them. Addition of 500 microM hydrogen peroxide (H2O2) to the 50 microM Fe(2+)-EDTA plus 500 microM VC further caused a 14-fold increase in .OH generation. Addition of H2O2 (500 microM) to the .OH generating mixture induced more conspicuous myocardial changes compared with the mixture without H2O2 addition, but the extent of those changes other than increase in coronary flow was less than that caused by perfusion with 500 microM H2O2 alone. These results further suggest that the cardiac changes induced by the .OH generating system are due to the combined effects of .OH and H2O2 which is formed as an intermediate product.