ABSTRACT
Dl-tetrahydropalmatine (THP) 5 ~ 15 mg ? kg-1 iv markedly reduced the incidences of cardiac arrhythmias and myocardial lipidperoxide content after reperfusion of the is-chemic myocardium in rats. In isolated rat ventricular muscles, THP 1,3 and 10 ?mol?L-1 shifted the concentration-effect curves for phenylephrine to the right unparally, together with decreasing their maximal responses,exhibiting a non-competed antagonistic action. It was also found that THP 10 ?mol?L-1was able to reduce the amplitude of delayed afterdepolar-izations and to stop triggered activity and/or ab-normal automatic activity induced by reoxygena-tion of hypoxic myocardium in isolated ventricular muscles of guinea pig. These results suggest that the protective effects of THP might be attributed, at least in part, to the depression of delayed afterdepolarizations and the prevention of oxygen free radical injury without the involvement of the cardiac ?1-adrenoceptors.