Ketamine inhibits the anticholinesterase activity of ranitidine and physostigmine.

ABSTRACT

1. The present study was performed to investigate the effect of ketamine on the contractile responses induced by the H2-receptor antagonist ranitidine and the anticholinesterase agent physostigmine on the isolated guinea pig ileum. 2. The contractile responses induced by ranitidine and physostigmine on the guinea pig ileum were significantly prevented, in a concentration-dependent manner, by ketamine, while the ones induced by acetylcholine were not modified. The contractile responses induced by acetylcholine were inhibited by exogenous acetylcholinesterase. Ranitidine and physostigmine inhibited the above reduction, and this effect was significantly prevented by ketamine in a concentration-dependent manner. 3. These findings show that ketamine inhibits the contractile effect of ranitidine and physostigmine on the guinea pig ileum. This inhibition caused by ketamine seems to be associated with the protection of acetylcholinesterase against the inhibition by ranitidine and physostigmine.