Stereospecific antiarrhythmic effects of naloxone against myocardial ischaemia and reperfusion in the dog.

1. The effects of both the (-)- and (+)-stereoisomers of naloxone in anaesthetized dogs with arrhythmias induced by acute coronary artery occlusion followed by reperfusion were investigated. 2. Following coronary artery occlusion and reperfusion, all dogs in the control group developed ischaemia- and reperfusion-induced cardiac arrhythmias, bradycardia and hypotension. 3. The opiate antagonist (-)-naloxone prevented the arrhythmias, bradycardia and hypotension due to myocardial ischaemia and reperfusion. 4. The (+)-stereoisomer of naloxone, which is inactive as an opiate antagonist, was without beneficial effects. 5. These results indicate a possible involvement of endogenous opioid peptides in the cardiac effects due to myocardial ischaemia and reperfusion, mediated by opiate receptors through opiate antagonism.