Anti‐arrhythmic activities of opioid agonists and antagonists and their stereoisomers

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Abstract
1 A series of opioid agonists, antagonists and their (+)-stereoisomers were tested for antiarrhythmic activity in the rat coronary artery occlusion model. 2 Naloxone (0.01–2 mg kg−1) significantly reduced the incidence and severity of cardiac arrhythmias, in accordance with previous published studies. 3 The non-opioid stereoisomer, (+)-naloxone, was equipotent with naloxone against occlusion-induced arrhythmia. 4 Similar non-stereospecific antiarrhythmic effects were induced by another opioid antagonist, Win 44,441–3 and its stereoisomer Win 44,441–2. 5 The opioid agonists, morphine and levorphanol, protected against occlusion-induced arrhythmia as did the opioid antagonists, and the (+)-stereoisomer, dextrorphan, was equipotent to levorphanol. 6 It is concluded that the antiarrhythmic effects of opioid drugs are not mediated by opioid receptors. A direct effect on ionic currents in cardiac muscle is suggested as the mechanism of opioid antiarrhythmic activity.