Protective effects of non-peptide endothelin receptor antagonist bosentan on myocardial ischaemic and reperfusion injury in the pig

OBJECTIVE: The aim was to investigate the effects of the non-peptide endothelin receptor antagonist bosentan (Ro 47-0203) on haemodynamic variables, infarct size, myocardial overflow, and tissue content of endothelin-like immunoreactivity (ET-LI) during ischaemia and reperfusion in anaesthetised pigs, and to study the inhibitory effect of bosentan on ET-1 induced coronary constriction in vitro. METHODS: Ischaemia was induced by ligation of the left anterior descending coronary artery for 45 min, followed by 4 h of reperfusion. Bosentan was given either intravenously (5 mg.kg-1) 15 min before ischaemia or as a 25 min local coronary venous retroinfusion (10(-4) M) starting at 30 min of ischaemia. ET-LI was analysed in myocardial tissue and in plasma from the anterior interventricular coronary vein and aorta. The effect of bosentan on endothelin-1 induced vasoconstriction was evaluated in isolated diagonal branches of left anterior descending coronary artery. RESULTS: Intravenous bosentan slightly reduced arterial blood pressure (P < 0.05) but did not affect basal coronary vascular resistance. Local retroinfusion of bosentan did not change blood pressure. Intravenous and retroinfused bosentan significantly reduced infarct size by 58% and 48% respectively (P < 0.01) and enhanced the recovery of coronary blood flow by 65-90% compared to vehicle treated controls at the end of 4 h reperfusion. The basal plasma levels of ET-LI and the myocardial overflow of ET-LI during reperfusion increased twofold after bosentan. A threefold increase in the concentration of ET-LI was observed in the ischaemic/reperfused myocardium and this enhancement was significantly attenuated by bosentan. Bosentan effectively antagonised the endothelin-1 induced but not the serotonin induced, contractions of isolated coronary arteries and reversed the established contraction induced by endothelin-1. CONCLUSIONS: The non-peptide endothelin receptor antagonist bosentan markedly protects the myocardium from ischaemia/reperfusion injury and improves blood flow to the reperfused area, indicating the involvement of endogenous endothelin-1 and the therapeutic value of bosentan in the treatment of ischaemia/reperfusion injury.