Estimates of free-radical production in rat and swine hearts: method and application of measuring malondialdehyde levels in fresh and frozen myocardium.

Toxic peroxides result when oxygen radicals react with various peroxidic precursors in tissue or blood. A colorimetric method based on reactions of malondialdehyde (MDA), a key intermediate in the formation of peroxides, has been described in fresh tissues. The present report adapts this assay to measure MDA levels in frozen heart muscle from rats and swine. Mean tissue values of MDA ranged from 154-353 nmol/g (n = 13) in fresh rat hearts perfused by the Langendorff technique. Values in frozen samples were 228 +/- 14 nmol MDA/g (n = 22). When mechanical function was increased in isolated working rat hearts, tissue MDA levels decreased by -25 delta % (P less than 0.025). In working swine hearts, increasing perfusate levels of unsaturated fatty acids caused a 42% increase in tissue MDA levels, P less than 0.001. Suppressing fatty acid oxidation with either oxfenicine or low flow ischemia caused no significant shifts in peroxide contents. Thus, the thiobarbituric acid method for MDA measurements is well adapted to analyzing frozen myocardium, and MDA levels appear sensitive to alterations in mechanical function and the presence of excess fatty acids.