DISSOCIATION BETWEEN THE EFFECTS OF FENTANYL AND ALFENTANIL ON SPONTANEOUS AND REFLEXLY EVOKED CARDIOVASCULAR RESPONSES IN THE DOG

Observations were made for 3 h in 10 anaesthetized dogs on theeffects of alfentanil 500 µg kg ^– andfentanyl 100µg kg^–1 on resting heart rate (HR) and mean arterialpressure (MAP), and on the changes evoked in heart rate andmean arterial pressure ( HR and MAP) by stimulation of a cutaneousnerve. Both drugs caused similar decreases in the resting HR(43%44%) and MAP (28–31%), which returned to baselinewithin lgOmin following alfentanil but not fentanyl. Fentanyldecreased the somato - cardiovascular reflexes by 73% and 82%compared with a significantly smaller reduction of 54% and 55%(P< 0.05) with alfentanil. Following nlffntanilj MAP hadrecovered by 15 min and HR by 70 min compared with 70 and 90nun respectively for fentanyl. In conclusion, there was a dissociationbetween the maximum effect of alfentanil and fentanyl on theresting circulation and on the evoked cardiovascular reflexes.With both drugs a dissociation was observed between the durationsof their effect on the resting cardiovascular system and onthe evoked cardiovascular responses ^*Present address: Department of Anaesthetics, Tzanion Hospital,Piraeus, Greece