Sympathetic Efferent Nerve Activity in Conscious and Isoflurane-anesthetized Dogs

Open Access
Publisher Website
Google Scholar
Abstract
The hypotension accompanying isoflurane [IF] suggests that the anesthetic produces an attenuation of sympathetic tone. Previous studies examining the effects of IF on sympathetic efferent nerve activity have required concomitant use of a basal anesthetic or decerebration, both of which independently alter sympathetic activity. This study was performed to examine the effects of IF on sympathetic efferent nerve activity in the absence of basal anesthetic or decerebration. Five mongrel dogs were anesthetized with 4% IF by mask. Platinum electrodes were chronically implanted around a renal nerve adjacent to the renal artery in order to measure renal sympathetic efferent nerve activity in the conscious and anesthetized animals. After 5-24 h for recovery renal nerve activity and arterial pressure (via an implanted femoral artery cannula) were measured in the conscious resting animal (control), during induction (4% IF) and intubation, in the anesthetized animal (1.5% and 2.5% IF) and during recovery and extubation. IF produced a significant dose-dependent depression of arterial blood pressure but did not significantly change heart rate. Renal sympathetic effect nerve activity at 1.5% IF was not significantly different from that in conscious animals but nerve activity at 2.5% IF was depressed significantly from both control and 1.5% IF. Both intubation and extubation were accompanied by an increase in sympathetic nerve activity. IF appeared to directly depress sympathetic activity at both levels of anesthesia but the direct depression of activity at 1.5% IF seemed to be countered by reflex increases in sympathetic tone due to hypotension accompanying anesthesia. Central depression of reflex activity by 2.5% IF combined with direct depression of sympathetic efferent activity resulted in the attenuation of renal nerve activity.