Negative chronotropic but no antiarrhythmic effect of (+)- and (-)-naloxone in rats and guinea pigs.

STUDY

OBJECTIVE

The aim was to investigate the antiarrhythmic effects of (+)- and (-)-naloxone in various arrhythmia models in vivo.

DESIGN

Naloxone (1-40 mg.kg-1), naltrexone (20-40 mg.kg-1), or standard antiarrhythmic drugs (quinidine, lignocaine, phenytoin, (+)-sotalol) were injected intravenously. Ventricular extrasystoles were then elicited by infusion of either ouabain (guinea pigs) or aconitine (rats), or by electrical stimulation (guinea pigs).

EXPERIMENTAL MATERIAL: Male Wistar rats and guinea pigs (n = 6-10) were used. Arterial blood pressure and ECG were recorded continuously.

MEASUREMENTS AND MAIN

RESULTS

Naloxone and naltrexone decreased the heart rate. The effect of naloxone was not stereospecific and is apparently not mediated by opioid receptors. Naloxone had no influence on ouabain induced arrhythmias or fibrillation threshold in guinea pigs. The appearance of aconitine induced extrasystoles was accelerated by 20 mg.kg-1 (-)-naloxone but delayed by 40 mg.kg-1. No effects were seen with (+)-naloxone or (-)-naltrexone.

CONCLUSIONS

The results show that naloxone does not possess prominent antiarrhythmic properties.