EFFECTS OF CHOLINERGIC AGONISTS ON VIP RELEASE FROM MEISSNER’S PLEXUS OF RABBIT ILEUM

To characterize the types of cholinergic receptors which mediate the release of vasoactive intestinal polypeptide (VIP) from submucosal neurons of the ileum, we studied the effects of specific cholinergic agonists on VIP release from rabbit ileum in virro. A piece of rabbit ileum containing mucosa and submucosal plexus was mounted for perfusion in Ussing chamber, and VIP release into the mucosal and serosal solutions was determined every 15 min. The addition of a nicotinic agonist, dimethylphenylpiperazinium (DMPP), to the serosal solution caused a dosedependent increase in VIP release into the serosal solution. Such DMPP-induced VIP release was blocked by hexamethonium (nicotinic antagonist), or tetrodotoxin (neurotoxin), but not by atropine (muscarinic antagonist). McN-A-343 (specific M1 muscarinic receptor agonist) and bethanechol (specific M2 muscarinic receptor agonist) had no effect on VIP release into the perfusing solution. These results provide convincing evidence that activation of nicotinic receptors in submucosal Meissner’s plexus results in the release of VIP.