Objectives: To differentiate the impact of the beta-blocking and the anti-oxidant activity of carvedilol in maintaining myocardium viability.
Methods: Isolated rabbit hearts, subjected to aerobic perfusion, or low-flow ischaemia followed by reperfusion, were treated with two doses of carvedilol, one dose (2.0 microM) with marked negative inotropic effect due to beta-blockage and the other (0.1 microM) with no beta-blockage nor negative inotropism. Carvedilol was compared with two doses of propranolol, 1.0 - without - and 5.0 microM - with negative inotropic effect. Anti-oxidant activity was measured as the capacity to counteract the occurrence of oxidative stress and myocardium viability as recovery of left ventricular function on reperfusion, membrane damage and energetic status.
Results: Carvedilol counteracted the ischemia and reperfusion induced oxidative stress: myocardial content of reduced glutathione, protein and non-protein sulfhydryl groups after ischaemia and particularly after reperfusion, was higher in hearts treated with carvedilol, while the myocardial content of oxidised glutathione was significantly reduced (0.30+/-0.03 and 0.21+/-0.02 vs. 0.39+/-0.03 nmol/mg prot, both P<0.01, in 0.1 and 2.0 microM). At the same time, carvedilol improved myocardium viability independently from its beta-blocking effect. On the contrary, propranolol maintained viability only at the higher dose, although to a lesser extent than carvedilol. This suggests that the effects of propranolol are dependent on energy saving due to negative inotropism. The extra-protection observed with carvedilol at both doses is likely due to its anti-oxidant effect.
Conclusions: Our data show that the anti-oxidant activity of carvedilol is relevant for the maintenance of myocardium viability.