Abstract

Rabbit ileal mucosa, when mounted in a flux chamber and stimulated with a 5 Hz electrical field (EFS), secretes Cl, a change reflected in an increase in short circuit current (Iac). Because the EFS response is eliminated by agents which prevent neural transmission, the mediator is most likely a neurotransmitter present in nerves lying close to the secreting epithelium. To identify the chemical mediators of the response, we determined the effects of receptor antagonists, agonist desensitization and other agents on the Isc response to EFS. Because of the failure of antagonists or desensitization to affect the response to EFS, we eliminated the following agents as possible mediators: acetylcholine (pre- and postganglionic), norepinephrine, dopamine, 5-hydroxytryptamine, histamine, prostaglandins, adenosine triphosphate, bombesin, neurotensin and Substance P. Pyrilamine, diphenhydramine and cyproheptadine in high concentration (0.1 mM) reduced markedly the Isc response to EFS for reasons unrelated to histamine antagonism. Although acetylcholine has been shown in the ileum of humans and of guinea pigs to mediate up to half of the Isc response to EFS, the identity of the mediator(s) in rabbit ileum remains unknown.