Silymarin and vitamin E do not attenuate and vitamin E might even enhance the antiarrhythmic activity of amiodarone in a rat reperfusion arrhythmia model.

Oxidative stress and lysosomal phospholipoidosis, which also might be partly attributed to free radicals induced by amiodarone (AM), may be involved in AM toxicity, which can be prevented by antioxidants. Our aim was to study if vitamin E (E) or silymarin (S), a lipid and a water-soluble antioxidant, modified the antiarrhythmic efficacy of AM in a rat reperfusion arrhythmia test. The following groups of male Sprague-Dawley rats (15 rats/group) were treated by gavage once a day for 4 weeks: 1. methylcellulose (MC, 0.4%), 2. sunflower seed oil (SSO), 3. AM, suspended in MC (30 mg/kg), 4. E, dissolved in SSO (100 mg/kg), 5. AM + E, 6. S, suspended in MC (80 mg/kg), 7. AM + S. The mean duration of ventricular tachycardia + fibrillation (MDVT + VF) and sinus rhythm (MDSR) the incidence of ventricular fibrillation (VF) and ventricular tachycardia (VT) and mortality were measured during a 10-min reperfusion after a 5-min coronary artery occlusion in anaesthetized rats. An arrhythmia score, representing the combined incidence and duration of different types of ventricular arrhythmia, was calculated. Compared with the MC group, MDSR was longer and MDVT + VF was shorter in all drug treated groups and in the SSO group. In the AM + E treated group MDSR was prolonged more and MDVT + VF was shortened more than in the AM, E or SSO groups. Compared with the MC group, the incidence of VF and mortality was similarly decreased in the SSO group and in most drug treated groups. No significant difference in the incidence of VT was found among all groups. The arrhythmia score was reduced by all drug treatments. Combined treatment with AM + E decreased arrhythmia score more than treatment with AM or SSO alone, but arrhythmia score was similar in the AM + E and E groups. In conclusion, both AM and antioxidant treatments alone or together resulted in a marked reduction of reperfusion arrhythmias in this model. SSO also exerted a moderate antiarrhythmic effect. Antioxidants administered together with AM did not attenuate and E might have even enhanced the antiarrhythmic effect of AM, therefore the combination of antioxidants with AM may be advantageous to reduce AM toxicity.