Antiarrhythmic action of naloxone: direct, non-opiate effect on the rat heart.

The opiate antagonist naloxone reduced the incidence and severity of cardiac arrhythmia induced in rats by intracarotid administration of adrenaline. Naloxone also reversed the adrenaline-induced arrhythmia in isolated heart preparations, suggesting a local antiarrhythmic action of the opiate antagonist. Similar effects were obtained with the (+) stereoisomer of naloxone which is inactive as an opiate antagonist. Thus, the direct action of naloxone at the rat heart is probably not mediated by opiate receptors.