No evidence of malonyldialdehyde formation during reoxygenation injury in vitamin E-deficient rat heart

Vitamin E is an endogenous antioxidant and is known to afford protection against lipid peroxidation. If lipid peroxidation was an important factor in the pathogenesis of reoxygenation injury in heart, then both the extent of lipid peroxidation and cell injury would be expected to be exacerbated in vitamin E-deficient hearts. To study reoxygenation injury in the present experiments, rat hearts were perfused in the Langendorff mode with a modified Krebs-Henseleit buffer under anoxic conditions for 60 min before resuming normoxic perfusion for 20 min. Creatine phosphokinase (CPK) activity and malonyldialdehyde (MDA), a product of lipid peroxidation, were assayed in the perfusate effluent from hearts during reoxygenation injury. Also, myocardial MDA and vitamin E contents were measured in extracts of freeze-clamped heart tissue obtained immediately before and 2 min after reoxygenation. Experiments were performed on hearts from groups of weanling rats fed either a vitamin E-deficient or vitamin E-supplemented diet (50 I.U. vitamin E/kg) for 5 to 6 weeks. After 5 weeks, the myocardial vitamin-E content was 103.8±5.3 (n=5) and 11.5±1.6 (n=4) ng/mg protein (mean±SEM) in the vitamin E-supplemented and vitamin E-deficient groups respectively. Perfused hearts from both dietary groups showed a peak of enzyme release 2 to 3 min after the reintroduction of oxygen, and enzyme release from vitamin E-deficient hearts was two-fold greater than enzyme release from vitamin E-supplemented hearts. MDA was not detected in the effluent perfusate of either group of hearts (<0.24 nmol MDA/min/g wet wt) and the myocardial MDA content was not altered by diet or reoxygenation. There was no evidence that myocardial vitamin E was consumed during reoxygenation. In conclusion, vitamin E was found to afford significant protection against reoxygenation injury and this is consistent with the involvement of free radicals in the injury process. However, MDA was not detectable in the coronary effluent or heart tissue during the first 20 min of reoxygenation injury, even in vitamin E-deficient hearts, suggesting that it is a relatively unimportant event in the early pathogenesis of reoxygenation injury.