Dose-dependent effects of propofol on renal sympathetic nerve activity, blood pressure and heart rate in urethane-anesthetized rabbits

To evaluate the role of the autonomic nervous system in hemodynamic changes after propofol bolus injection, we used direct recordings of renal sympath etic nerve activity to examine the dose-dependent effects of propofol (2.5, 5, 10, and 20 mg/kg) on heart rate, mean blood pressure and renal sympathe tic nerve activity in urethane-anesthetized rabbits. The animals were divid ed into four groups: animals with an intact neuraxis (intact group), cervic al vagal nerve-sectioned animals (vagotomy group), carotid sinus and aortic -nerve sectioned animals (SAD group), and animals with SAD plus vagotomy (S ADV group). Heart rate did not change significantly even after administrati on of 2.5 and 5 mg/kg but decreased markedly on 20 mg/kg injection in all g roups. The intact and vagotomy groups had augmented renal sympathetic nerve activity with insignificant changes in mean blood pressure after 5 mg/kg i njection of the agent. Insignificant changes of renal sympathetic nerve act ivity but a remarkable decrease of mean blood pressure appeared after 10 mg /kg propofol. Sustained hypotension in parallel with a profound depression of renal sympathetic nerve activity developed at the dose of 20 mg/kg. In S AD and SADV groups, however, dose-dependent depressions of renal sympatheti c nerve activity were accompanied by decreases of mean blood pressure. Thes e results suggest the following: (1) propofol-induced hypotensive effects a re probably produced by the central-mediated sympathetic depression. (2) Th e baroreceptor reflex may be preserved at the lower dose of the agent. (3) Heart rate does not change significantly unless a large dose of propofol is used. The difference in effects on heart rate and on mean blood pressure m ay denote a greater inhibition of sympathetic vascular outflow than of the cardiac sympathetic outflow regulating cardiac rate and contractility. This hypothesis needs further clarification. (C) 2000 Elsevier Science B.V. All rights reserved.