Effects of resibufogenin on monophasic action potential and contractile force of rabbit heart in situ

The pharmacological effects of resibufogenin (RBG), an effective cardiotonic obtained from the traditional Chinese medicine Chansu, on the electrical activity and cardiac contractile force of the rabbit heart (n=20) in situ were studied using a new technique for recording monophasic action potential (MAP). RBG (0.3 mg/kg. iv) reduced the MAP amplitude. decreased the heart rate. shortened the MAP duration and gradually increased the cardiac contractile force. In addition, the reduction of the delayed afterdepolarizations (DADs) by RBG were observed for the first time in the left ventricle of the rabbit heart in situ. The characteristics of the DADs were similar to those previously described in cardiac fibers in vitro. The above results are identical to the in vitro effects of RBG on single cardiac fibers. The double direction effects of RBG on the monophasic action potential duration are discussed.