DIRECT COMPARATIVE EFFECTS OF ISOFLURANE AND DESFLURANE ON SYMPATHETIC GANGLIONIC TRANSMISSION

Although the sympathetic ganglion is an important site of peripheral r egulation, few studies have examined the effect of anesthetics on syna ptic transmission. In the present study we compared the actions of des flurane with those of isoflurane on synaptic transmission and neurotra nsmitter release in the stellate ganglion. In the electrophysiologic g roup, 14 stellate ganglia were isolated from adult mongrel dogs after halothane anesthesia, desheathed, and superfused with Krebs' solution. Compound action potentials (CAP) were induced by supramaximal stimula tion of the preganglionic T3-ramus at a low frequency of 0.4 Hz and we re recorded from the postganglionic ventral ansa subclaviae. Each gang lion was exposed to two levels of anesthetics (equivalent to 1 and 2 m inimum alveolar anesthetic concentration [MAC]), followed by an anesth etic-free washout period. While equianesthetic concentrations of isofl urane and desflurane caused essentially equipotent suppression of gang lionic transmission, desflurane was more efficacious than isoflurane, both with respect to the onset of and recovery from the inhibition of synaptic activity. In the electrochemical group, 25 ganglia were expos ed to both anesthetics at a high concentration (equivalent to between 1.82 and 1.95 MAC) during maximal and submaximal current stimulations, and the release of actylcholine (ACh) in the superfusate was measured with liquid chromatography. Although desflurane and isoflurane caused a significant depression of CAP, neither anesthetic inhibited the rel ease of ACh in the superfusate at either maximal or submaximal current stimulations. These results indicate that the suppression of ganglion ic activity is equipotent for both anesthetics based on equivalent MAC values, but that desflurane is more efficacious than isoflurane with respect to onset and recovery at the higher concentrations of anesthet ics. The source of impaired conduction appears to be a reduced sensiti vity to neurotransmitter release in the postsynaptic neuron.