EFFECTS OF TETRAMETHYLPYRAZINE ON CARDIAC HAEMODYNAMICS IN DOGS

The effects of tetramethylpyrazine (TM) on femoral, cerebral and coronary blood flow and cardiac function were examined in 18 anesthetized dogs. Intravenous infusion of TM (1, 2, 4 mg/kg/min for 10 min) produced a dose-dependent positive inotropic, chronotropic and vasodilatory effect. The HR, LVP and LV dp/dt max were increased by infusion of TM 1 or 2mg/kg/min. During administration of TM 4 mg/kg/min, these effects were found to be more marked. In addition, a significant increase in cardioindex (CI) and left ventricular end diastolic pressure (LVEDP) and a decrease of total peripheral resistence (TPR) were observed.Blood flow was measured by means of electromagnetic flow meter. Administration of TM 4 mg/kg/min induced an augmentation of the coronary and cerebral blood flow and reduction of their vascular resistence, while the myocardial O₂ consumption was elevated. The cardiotonic and vasodilatory effects induced by TM in anesthetized dogs could be antagonized by iv propranolol (1 mg/kg), but not abolished by im reserpine 0.2～0.3mg/kg 24 hours before TM administration.In one spontaneous and four renal hypertensive dogs, TM (infusion of 4mg/kg/min or a single iv dose of 20mg/kg) also elicited a positive chronotropic effect. This effect disappeared after iv injection of 2mg/kg propranolol. It appears that the cardiohaemodynamic effects elicited by TM is mediated through β-Adrenoreceptor activation.