Centrally induced cardiovascular effects and kinetic behaviour of isoarecaidine propyl ester in the cat

The present investigation deals with effects of isoarecaidine propyl ester (IAPE) on blood pressure and heart rate of the anaesthetized cat. The kinetic behaviour of the drug in plasma and various brain tissues was also studied. The results indicate that the ester (4 mg.kg-1) induces a depressor effect and bradycardia after i.v. administration. Injection of IAPE (up to 60 micrograms.kg-1) into the left vertebral artery lowers blood pressure in a dose-dependent manner. When administered simultaneously into the left and right vertebral artery, low doses (6 micrograms. kg-1) produce a substantial fall in blood pressure. Although the fall in blood pressure after i.v. injection lasts for more than 60 min, plasma half life is extremely short (t1/2 = 6.3 sec). The possible metabolism of the ester was studied in the pons, medulla oblongata and cerebellum. Thirty min after the injection into the left vertebral artery, IAPE is almost entirely hydrolyzed in the pontomedullary region. This degradation is prevented by pretreatment with paraoxon, that abolishes the depressor action of IAPE. It is suggested that accumulated isoarecaidine in the pontomedullary region is responsible for the depressor response to IAPE. Since IAPE does not seem to influence blood pressure and heart rate via a peripheral mechanism and lowers blood pressure and cardiac frequency by a central action, this drug is considered to be of pharmacological interest. The mechanism of action is discussed.