Anti-arrhythmic action of l-tetrahydropalmatine

l-Tetrahydropalmatine (THP) 6 and 12 mg/kg iv converted ouabain-induced ventricular tachycardia into sinus rhythm in rabbits; while 15 and 30 mg/kg antagonized the arrhythmias induced by picrotoxin (icv). At the dose of 30 mg/kg (ip), some protective effects against aconitine arrhythmias appeared in anesthetized rats. THP 45 and 60 mg/kg iv decreased the onset of CaCl2-ACh-induced atrial fibrillation in mice. Intravertebroarterial or icv injection of 6 mg THP per rabbit also antagonized arrhythmias induced by ouabain and hypothalamic electric stimulation. Pretreatment with reserpine and hexamethonium only reduced but not abolished the anti-arrhythmic effect of THP on ouabain-induced arrhythmias. It is suggested that the anti-arrhythmic action of THP is mainly mediated through the peripheral mechanism but partially through central action.