Failure of naloxone or physostigmine to reverse nitrogen anesthesia in guinea pigs

Stress as well as anesthesia has been reported to stimulate endorphin release. The possibility that the stress of compression at 1 atm/min or nitrogen anesthesia, or both, might release endorphins was tested in guinea pigs with the use of naloxone--a narcotic antagonist, and physostigmine--a cholinesterase inhibitor. The animals received i.p. equal volumes of either drugs or the placebo just before compression to 32 ATA (oxygen less than or equal to 1 ATA). The pressure at loss of righting reflex was compared. Nitrogen anesthesia occurred at mean pressures ranging from 26.9 to 27.8 ATA, with no statistical differences demonstrated in all groups. It is concluded that 1) neither naloxone nor physostigmine reversed nitrogen narcosis and 2) stress of compression or nitrogen narcosis, or both, failed to show effects attributable to increased endorphin release.