Pharmacology of the inhibitory innervation in the gastroduodenum of Sprague Dawley rat: An in vivo study.

Intrinsic inhibitory innervation of the mammalian gut is non-adrenergic and non-cholinergic (NANC) in nature. Candidate NANC inhibitory transmitters include ATP, VIP and nitric oxide (NO) and there is considerable evidence for multiple NANC inhibitory nerve types. The goal of the research presented here was to determine the nature of the neurotransmitter(s) mediating relaxant motor activity in the rat gastroduodenum in vivo. Duodenal motor activity was patterned into 'Grouped' (periods of intense motor activity) interposed with 'Intergroup' periods of low motor activity. Spontaneous relaxant activity in the rat gastroduodenum can thus be differentiated: antral and duodenal 'Intergroup' relaxations are NO dependent and GABA$\rm\sb{A}$ receptors mediate the pathways controlling these relaxations. The pathway(s) controlling 'Intergroup' NO relaxations involve functional ATP$\rm\sb{2y}$ receptors. 'Grouped' relaxations are mediated by ATP via ATP$\rm\sb{2x}$ receptors and are modulated by NO. Lastly, VIP can evoke relaxations of (i) the antral longitudinal smooth muscle by targeting the A-GABAergic-nitrergic pathway and (ii) the antral circular muscle either directly or via a neural pathway, both of which involve NO. (Abstract shortened by UMI.