Central beta-endorphin release and recovery after exposure to nitrous oxide in rats.

To explore the hypothesis that nitrous oxide stimulates the beta-endorphin system in vivo, rats were exposed to nitrous oxide/oxygen at variable concentrations for one hour. beta-Endorphin concentration at sites along the neuraxis functionally involved with analgesia was elevated in nitrous oxide-exposed animals. The increase in beta-endorphin concentration was statistically significant at nitrous oxide concentrations of 60 and 80%. This elevation of beta-endorphin levels depended on the concentration of nitrous oxide delivered rather than on the duration of exposure. With cessation of nitrous oxide anesthesia, beta-endorphin concentration returned to control levels within 30 minutes.