Antagonism of Nitrous Oxide Analgesia by Naloxone in Man

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Abstract
The possible reversal of N2O analgesia by naloxone [NL] was investigated. Two studies were conducted in 21 healthy male subjects, who responded to ischemic pain produced by tourniquet applied to the upper arm for 15 min, while breathing air or N2O, 33%. Using a double-blind procedure, the subjects received i.v. injections of NL and saline solution on different days. In 8 subjects, NL, 8 mg, administered without N2O, had no effect on pain report. Unlike saline solution, NL, 8 mg, decreased significantly the analgesia induced by N2O. In 13 subjects, NL, 4 mg, also decreased significantly the effect of N2O analgesia in comparison with saline solution. NL showed its reversal effect mainly on sensory response ratings obtained during the painful stages of ischemia, between 11 and 15 min. Analgesia induced by N2O may be partly related to the opiate receptor-endorphin system in man.