Modulation of cholinergic transmission by nitric oxide, VIP and ATP in the gastric muscle

The influence of the putative inhibitory neurotransmitters nitric oxide (NO), vasoactive intestinal polypeptide (VIP) and adenosine 5'-triphosphate (ATP) was examined on the contractile responses elicited, either by electrical field stimulation (EFS) or exogenous acetylcholine (Ach), in strips of the circular muscle of the rabbit gastric corpus. Muscular contractions evoked by Ach were not influenced by the NO-releasing compound sodium nitroprusside (SNP), but were depressed by VIP and scarcely affected by ATP. In contrast, the putative inhibitory neurotransmitters all depressed or even blocked the neurally induced cholinergic contractions elicited by EFS. Therefore, NO, VIP or ATP, besides causing muscular relaxation, may modulate the cholinergic transmission at the pre- and/or post-junctional level in the nerve-muscle pathway.