The role of vasoactive intestinal polypeptide in the inhibition of antral and pyloric electrical activity in rabbits.

The nature of the neurotransmitter released by intramural non-cholinergic non-adrenergic inhibitory neurones and the type of vagal afferents involved in the inhibition of antral and pyloric electrical activity induced by vagal afferent stimulation were investigated in conscious rabbits in which both splanchnic nerves had previously been cut. The inhibitory effect of duodenal distension was reversed by bilateral thoracic vagotomy. Either intravenous or intra-aortic infusions of vasoactive intestinal polypeptide (VIP) inhibited the electrical activity of both antrum and pylorus for several minutes. Electrical stimulation of afferent vagal fibres and duodenal distension both inhibited antral and pyloric activity and produced a significant increase of portal plasma VIP concentration. Numerous VIP-immunoreactive fibres were found to be present in the muscular layers of the pylorus. The possibility that this form of inhibition is mediated by VIPergic fibres is discussed as is the likely involvement of vagal afferent fibres in the case of the response to duodenal distension.