Direct evidence that eseroline possesses morphine-like effects.

The opiate-like effects of eseroline, a physostigmine derivative, were studied in different tests. The antinociceptive effect of eseroline given s.c. and intracerebrally could be detected in the rat hot plate test and was reversed by naloxone. The apparent pA2 values of naloxone demonstrated with eseroline and morphine were found to be equal, suggesting an effect on similar receptors. Eseroline also had opiate agonist activity on the isolated longitudinal muscle strip of guinea pig ileum and isolated nictitating membrane of the cat: presynaptically, it inhibited the contractions evoked by stimulation and its effect was antagonized by naloxone. Eseroline reduced acetylcholine release from the myenteric plexus of the longitudinal muscle strip when the cholinesterases had been inhibited by physostigmine. In addition, it was also found that eseroline antagonized the inhibitory effect of normorphine in the longitudinal muscle strip and potentiated the effect of exogenous acetylcholine on smooth muscle, both effects being attributed to its anticholinesterase activity. The analgesic effect of eseroline was not related to its anticholinesterase activity.