The effects of nitrous oxide on the central endogenous pro-opiomelanocortin system in the rat.

The hypothesis that nitrous oxide stimulates the central pro-opiomelanocortin system in vivo was explored in this study. A concentration-dependent stimulation of central pro-opiomelanocortin neuropeptides was demonstrated after exposures to variable concentrations of nitrous oxide with oxygen. Rats exposed to 60% and 80% nitrous oxide with oxygen demonstrated an elevation of beta-endorphin concentration along the neuraxis involved with analgesia; no similar effect was observed in alpha-MSH concentration, neither duration of exposure nor acclimation to the enclosed environment altered this stimulation. The discontinuation of nitrous oxide exposure resulted in the diminution of beta-endorphin concentration to pre-exposure levels in 15-30 min. With an ACTH1-39 antisera, a semiquantitative increase in opiocortin immunoreactivity after exposures to nitrous oxide was demonstrated. In conclusion, the increase in beta-endorphin concentration and immunoreactive ACTH1-39 staining in the cells of origin, areas of fiber projection and terminal fields suggest that nitrous oxide stimulates the central pro-opiomelanocortin system in vivo in the rat.