OBJECTIVETo investigate the roles of sympathetic and vagus nerves in hypotension and bradycardia induced by fentanyl.

METHODSFourteen rabbits were divided into 2 groups: normal and vagotomized rabbits. Rabbits were anesthetized, paralyzed, and artificial ventilated. Right renal sympathetic nerve was exposed and prepared for recording electrical activity. Fentanyl was injected intravenously in incremental doses of 1, 4, 15, 30, and 50 microg/kg at 10 minutes intervals.

RESULTSFentanyl significantly reduced the spontaneous activity of renal sympathetic nerve, mean arterial pressure, and heart rate above a total dose of 20 microg/kg in both normal and vagotomized rabbits. However, normal rabbits spontaneous sympathetic nerve activity and mean arterial pressure were more depressed than vagotomized rabbits at total doses of 50 and 100 microg/kg. There were no significant difference in the reduction of heart rate between normal and vagotomized rabbits.

CONCLUSIONFentanyl induction of bradycardia and hypotension in rabbits is mainly due to depression of sympathetic nerve activity.

Analgesics, Opioid ; pharmacology ; Animals ; Blood Pressure ; drug effects ; Fentanyl ; pharmacology ; Heart Rate ; drug effects ; Kidney ; innervation ; Rabbits ; Sympathetic Nervous System ; drug effects ; physiology ; Vagotomy