Oxidative injury to myocardial membrane: direct modulation by endogenous alpha-tocopherol

Peroxidation of myocardial-membrane phospholipid is considered an important pathogenic component of heart muscle damage in ischemia and reperfusion. The extent to which membrane alpha-tocopherol (vitamin E) in the heart can modulate such damage and protect against it is a matter of controversy. The relative alpha-tocopherol deficit of spontaneously-hypertensive (SH) rat myocardium as compared to the myocardium of the Wistar-Kyoto (W/K) normotensive parent strain prompted use of these animals to identify and characterize any protective antiperoxidant role of endogenous, myocardial-membrane alpha-tocopherol. With exposure to a superoxide- and iron-containing initiator of peroxidation, the membrane complements from the ventricular myocardia of the SH rat and the W/K parent strain were found to have very different peroxidative-injury profiles. SH-rat myocardial membrane demonstrated a marked sensitivity to peroxidation as reflected in the acute onset and rapid progression of phospholipid damage. The greater susceptibility of SH-rat myocardial membrane to free-radical attack could not be explained by inter-strain compositional differences in membrane polyunsaturated fatty acids or fatty aldehydes. Rather, the basis for the enhanced peroxidation was identified as the 3-fold lower alpha-tocopherol content of SH-rat myocardial membrane with respect to the heart-muscle membrane from the normotensive animal. The relative alpha-tocopherol deficit not only increased the susceptibility of SH-rat cardiac membrane to damage under pro-oxidant conditions, but also reduced the efficacy of exogenously supplied antioxidant intervention. These findings demonstrate that membrane alpha-tocopherol tone is a critical protectant of myocardial phospholipid against oxidative injury and acts as a determinant of the course of heart-membrane peroxidative damage.