Effects of cocaine, cocaine metabolites and cocaine pyrolysis products on the hindbrain cardiac and respiratory centers of the rabbit.

Hemodynamic and respiratory effects of vertebral artery or i.v. administration of cocaine, cocaine metabolites and cocaine pyrolysis products were measured in anesthetized rabbits. Vertebral artery administration of 1 mg of cocaine produced decreases in blood pressure and heart rate and respiratory arrest. Cocaethylene (1 mg), a cocaine metabolite produced following co-administration of cocaine and ethanol, had comparable effects except that the respiratory arrest following cocaethylene had a longer duration of action than did cocaine. A decrease in blood pressure was also observed following 1 mg of norcocaine; however, unlike cocaine, norcocaine did not affect respiration. Acute tolerance was not observed to any of the effects of 1 mg of cocaine, cocaethylene or norcocaine following vertebral artery administration. None of these compounds had significant effects following i.v. administration of the same dose. The cocaine metabolites benzoylecgonine and ecgonine methyl ester were without effect by either route in doses up to 3 mg. In contrast to cocaine, the cocaine pyrolysis products anhydroecgonine methyl ester (3 mg) and noranhydroecgonine methyl ester (3 mg) produced similar effects via both routes of administration. Both compounds produced decreases in blood pressure and heart rate and an increase in respiratory rate. Anhydroecgonine ethyl ester (3 mg), a metabolite hypothetically formed from the cocaine pyrolysis product in individuals co-administering ethanol, had effects similar to the other pyrolysis products, although its effects were not as prominent via the i.v. route of administration. Acute tolerance was observed upon administration of the cocaine pyrolysis products. These results indicate that the cocaine pyrolysis products do not share a common mechanism of action with either cocaine or the cocaine metabolites.