Naloxone Has No Effect on Nitrous Oxide Anesthesia

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Abstract
Naloxone antagonizes general anesthesia in rats when the tail clamp is used as a painful stimulus to assess anesthesia. This antagonism may be due to the analgesic component of anesthesia only, and that anesthesia assessed by a non-painful stimulus would not be antagonized by naloxone. The anesthetic potency of N2O in mice was measured using loss of the righting reflex as a non-painful stimulus. Naloxone, 2 and 16 mg/kg, i.p., failed to antagonize N2O anesthesia measured 14-39 min after injection. Thus, 19 min after injection of naloxone, 2 mg/kg, the N2O ED50 was 1.25 .+-. 0.060 atm (n = 35), compared with 1.19 .+-. 0.053 atm (n = 35) after injection of saline solution (control). Following naloxone, 16 mg/kg, the N2O ED50 was 1.18 .+-. 0.059 atm (n = 35), compared with 1.22 .+-. 0.059 atm (n = 35) for saline solution. At neither dose of naloxone was the ED50 different from the control ED50.