Investigation of the mechanism of action of oxotremorine on the guinea-pig isolated ileum preparation.

1. The effects of oxotremorine on the guinea-pig ileum have been investigated to determine whether any component of its action is due to acetylcholine release.2. Log dose-response curves to oxotremorine and acetylcholine were similar and both drugs were competitively antagonized by atropine.3. Mipafox potentiated acetylcholine but not oxotremorine.4. No evidence of an indirect component of the action of oxotremorine was obtained using various pharmacological procedures (tetrodotoxin, morphine, cooling, procaine and hemicholinium-3).5. Oxotremorine had no effect on acetylcholine release from mipafox treated ileum but decreased the release from physostigmine treated ileum.6. It is concluded that oxotremorine acts directly on muscarinic receptors and not by releasing acetylcholine.