Time course of structure, function, and metabolic changes due to an exogenous source of oxygen metabolites in rat heart

Effects of xanthine (2 mM) and xanthine oxidase (10 U/L) perfusion on myocardial function, lipid peroxide content, high-energy phosphates and their metabolites, and ultrastructure were examined in isolated perfused rat hearts to define the time course of myocardial injury due to exogenous supply of active oxygen species. Peak-developed force and dF/dt showed a decline within 5 min and complete contractile failure was seen at 20 min. Resting tension was higher at 10 min and reached a maximum value of 400% at 40 min. These changes in contractile parameters were reduced by superoxide dismutase (1.2 × 105 U/L), catalase (2 and 4 × 104 U/L), and mannitol (10 and 20 mM). Lipid peroxide content was significantly higher at 5 min and rose continuously with xanthine – xanthine oxidase (X–XO) perfusion. A close correlation was noted (r = 0.935) between increased lipid peroxide content and a decrease in peak-developed force. Creatine phosphate and adensoine triphosphate (ATP) showed a time-dependent decrease due to X–XO perfusion. Loss of ATP also correlated (r = 0.819) with the contractile failure. Adenosine diphosphate showed an increase at 5 min followed by a decrease at 20 and 40 min. Adenosine monophosphate, adenosine, and creatine content increased with X–XO perfusion. In a semiquantitative morphometric study, significant myocardial and vascular changes became apparent only after 10 min of X–XO perfusion. When a 5-min perfusion with X–XO was followed by a control perfusion, a recovery of developed force and normal structure was noted at 40 min. These data show that X–XO induced contractile failure involves partially reduced forms of oxygen such as superoxide, hydroxyl radicals, and hydrogen peroxide. The negative inotropic effect of a vascular supply of these active oxygen species may be related to increased lipid peroxidation as well as the loss of high-energy phosphates. Structural damage to myocytes and blood vessels and a rise in resting tension were delayed events requiring a continuous and longer exposure to radical species.Key words: myocardial failure, oxygen radicals, lipid peroxidation, myocardial high-energy phosphates, myocardial cell damage, antioxidant protection.