Protective effects of All-trans-retinoic acid against cardiac arrhythmias induced by isoproterenol, lysophosphatidylcholine or ischemia and reperfusion.

Previous studies have shown that free polyunsaturated fatty acids (PUFA) reduce the excitability of cardiac myocytes and exert antiarrhythmic effects. Therefore, we hypothesized that retinoic acid (RA, vitamin A acid), which has structural characteristics similar to those of PUFA, may have similar antiarrhythmic effects. To test this hypothesis, we used an isolated, spontaneously beating, neonatal rat cardiac myocyte preparation to examine the effects of RA, added to the perfusion solution, on the cell contraction and arrhythmias induced by isoproterenol (ISO) or lysophosphatidylcholine (LPC). All-trans-RA (10-20 microM) induced a marked and reversible reduction in the contraction rate of the cell in 2-5 min without changing the amplitude of the contractions. Superfusion of the myocytes with either ISO (3 microM) or LPC (5 microM) induced sustained tachyarrhythmias characterized by spasmodic contractures and fibrillation. Addition of 15-20 microM all-trans-RA to the perfusion solution effectively prevented as well as terminated the arrhythmias induced by ISO and LPC. Furthermore, in a whole-animal model of arrhythmia in which the left anterior descending coronary artery (LAD) of the anesthetized rat was occluded for 15 min followed by reperfusion, both the incidence and severity of ventricular tachycardia and fibrillation (VT, VF) were significantly reduced during the ischemic and reperfusion periods by intravenous infusion of all-trans-RA. In contrast, other analogues, including retinol and retinal, and other fat-soluble vitamins, including vitamin D, E, and K, did not have such effects. Our results demonstrate that all-trans-RA can produce antiarrhythmic effects similar to those of PUFA, suggesting a novel role of RA as a potential antiarrhythmic agent.