Volatile anaesthetics antagonize nitrous oxide and morphine-induced analgesia in the rat

Abstract

We reported previously that nitrous oxide induces pre-emptive analgesia that is partially antagonized by naloxone and totally antagonized by halothane. The aims of this study were to determine if halothane and isoflurane are similar in this respect and to examine if volatile anaesthetics antagonize the analgesic effect of exogenous opioids. We found that 75% nitrous oxide prolonged tail-flick latency by 37% and this analgesia was dose-dependently inhibited by halothane and, less effectively, by isoflurane. In contrast, morphine 1.25 mg kg-1 i.v. also prolonged tail-flick latency by 35% but, unlike nitrous oxide-induced analgesia, this effect was attenuated only by high doses of halothane and was unaffected by isoflurane. Neither halothane nor isoflurane alone altered the tail-flick response. We conclude that both halothane and isoflurane dose-dependently antagonized nitrous oxide analgesia but antagonized morphine-induced analgesia to a lesser extent.

Effects of General Anesthetics on Substance P Release and c-Fos Expression in the Spinal Dorsal Horn

“…The synergistic interaction observed here parallels the behavioral literature. While some reports refer to the fact that volatiles such as halothane and isoflurane may antagonize nitrous oxide analgesia, 36 we saw no evidence of such a negative effect on substance P release of c-Fos activation here and nitrous oxide is MAC sparing when used with volatile anesthetics. 37-39 …”

Physiological Properties of the Lamina I Spinoparabrachial Neurons in the Rat

“…In our hands, considering the great responsiveness of numerous neurons to noxious stimuli, the analgesic effects of nitrous oxide did not seem to be very important. This could be due to the fact that the analgesic effect of nitrous oxide was counteracted, at least in part, by halothane as recently suggested (Goto et al 1994(Goto et al , 1996. In addition, nitrous oxide as well as halothane could separately interfere with spinal sensitization (Goto et al 1994;O'Connor et al 1995) and thus diminish the number of sensitized NS neurons that consequently appeared as WDR-like.…”

Can Determining the Minimum Alveolar Anesthetic Concentration of Volatile Anesthetic Be Used as an Objective Tool to Assess Antinociception in Animals?

“…It is not the first time that opposite effects between halogenated vapors and opioids have been reported in animal models (19,20). It is probable that the experimental conditions used have unmasked on opiate-induced excitatory effect on cardiovascular reactivity to noxious stimuli.…”