The role of cyclic AMP and phosphodiesterase activity in the mechanism of action of tetramethylpyrazine on human and dog cardiac and dog coronary arterial tissues.

The aim of the present experiments was to explore the underlying cellular mechanisms responsible for the actions of tetramethylpyrazine (TMP) on atrial, ventricular and coronary arterial tissues. Transmembrane potentials of cardiac tissues were detected by means of the glass microelectrode technique and contractile tension by a force transducer. Tissue cyclic (c) AMP level was determined by protein binding assay. Results show that in human atrial and dog Purkinje fibres, high concentration of TMP (3 mM) induced a persistent positive inotropic effect only in the presence of adrenaline. Also, 3 mM TMP increased the cAMP level of the atrial muscle fibres, especially in the presence of adrenaline. Determination of the activity of cAMP-phosphodiesterase revealed that 0.3 and 3 mM TMP inhibited the phosphodiesterase activity of dog coronary artery and human atrial tissues in a concentration-dependent manner. When compared at the lower concentration (0.3 mM), the inhibitory effect of TMP was about 60% that of theophylline. The above findings indicate that the cardiovascular effects of TMP are related to the inhibition of phosphodiesterase activity and the subsequent elevation of the cAMP concentration.