The free radical scavenger MDL 73,404 decreases infarct size and improves heart performance after myocardial ischaemia and prolonged reperfusion. In the present study the possibility that changes in receptor density might contribute to the MDL 73,404-induced increase in contractility has been investigated in rats subjected to myocardial ischaemia and 8 days of reperfusion. 2. Both in saline- and MDL 73,404-treated rats a significant decrease in beta1- and increase in beta2-adrenoceptor densities was apparent in the infarcted tissue. 3. In non-infarcted septum and right ventricle tissue ischaemia followed by reperfusion tended to increase the density of beta2-adrenoceptors which was significantly increased after MDL 73,404 treatment. 4. The increased density of beta2-receptors in the non-infarcted tissue may contribute to the MDL 73,404 induced improvement of cardiac performance.
