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

Objective: Increased antioxidant defence and altered G protein mediate d receptor signalling systems could be expected in myocardial precondi tioning. 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 t he porcine heart was induced by two occlusions of the mid left anterio r descending coronary artery for 10 min, with a 30 min reperfusion int erval. Left ventricular biopsies were obtained from control and precon ditioned 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 malondialdehy de were changed. There were no alterations in either the number of rec eptors (beta adrenergic, muscarinic and endothelin receptors) or the a mount of G proteins. Furthermore, the activity of adenylyl cyclase rem ained unchanged. Conclusions: No change in the antioxidant defence was demonstrated in preconditioned myocardium. This finding does not supp ort 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 precondition ed myocardium with regard to beta adrenergic, muscarinic, and endothel in receptors.