FREE-RADICAL SCAVENGING ENZYMES AND G-PROTEIN MEDIATED RECEPTOR SIGNALING SYSTEMS IN ISCHEMICALLY PRECONDITIONED PORCINE MYOCARDIUM

Objective: Increased antioxidant defence and altered G protein mediated receptor signalling systems could be expected in myocardial preconditioning. The myocardial antioxidant defence and the integrity of the G protein mediated receptor signalling systems were therefore examined in normal and preconditioned myocardium. Methods: Preconditioning in the porcine heart was induced by two occlusions of the mid left anterior descending coronary artery for 10 min, with a 30 min reperfusion interval. Left ventricular biopsies were obtained from control and preconditioned regions 30 min after the last occlusion. Results: In biopsies from the preconditioning region, neither the activities of superoxide dismutase or glutathione peroxidase, nor the content of malondialdehyde were changed. There were no alterations in either the number of receptors (beta adrenergic, muscarinic and endothelin receptors) or the amount of G proteins. Furthermore, the activity of adenylyl cyclase remained unchanged. Conclusions: No change in the antioxidant defence was demonstrated in preconditioned myocardium. This finding does not support the hypothesis that increased antioxidant defence could contribute to the cardioprotection of preconditioning. Additionally, an intact G protein mediated receptor signalling system was found in preconditioned myocardium with regard to beta adrenergic, muscarinic, and endothelin receptors.