Effects of levomepromazine, chlorpromazine and their sulfoxides on isolated rat atria.

The effects of levomepromazine, chlorpromazine and their sulfoxides were studied on spontaneously beating and on electrically driven rat atria in vitro. Levomepromazine, chlorpromazine and levomepromazine sulfoxide produced a dose-dependent decrease in the work index of spontaneously beating atria and in the contractile force of electrically driven atria, while chlorpromazine sulfoxide was relatively inactive in these respects. At higher concentrations, levomepromazine sulfoxide caused a pronounced increase in the threshold for electrical stimulation and the effective refractory period. Compared to chlorpromazine, levomepromazine looses less of its cardio-depressive effect through sulfoxidation.