Nutrients in the intestinal lumen initiate changes in motor function of the gastrointestinal tract. Intestinal lipid acts via a cholecystokinin A receptor- (CC.-AR) and a vagal afferent-dependent pathway. The hypothesis to be tested is that intestinal lipid- induced inhibition of gastric motility is dependent on absorption of lipid by enterocytes, formation and release of chylomicrons and apolipoprotein A-IV (apoA-IV), release of CCK. by apo A-IV and CCK acting on CCK-ARs on intestinal afferent nerve terminals. To test this hypothesis, studies are proposed to determine that: (1) inhibition of gastric emptying by lipid in the intestinal lumen depends on chylomicron formation and release of apo A-IV; (2) release of CCK in response to lipid is dependent on chylomicron formation and release of ap A-IV; (3) activation of vagal afferents in response to intestinal lipid is dependent on release of apo A-IV and CCK-AR activation and (4) to demonstrate the expression of CCK-AR on neuronal elements in the stomach and duodenum and their functional regulation by CCK. The role of chylomicron formation in lipid- induced inhibition of gastric emptying or motility and release of CCK will be determined in rats using the surfactant pluronic L81. Postabsorptive chylomicron products in mesenteric lymph will be given intra-arterially to demonstrate their effectiveness to inhibit gastric motility and act via a CCK-AR- and vagal capsaicin-dependent pathway. The role of apo A-IV in inhibition of gastric motility and CCK release in response to lipid will be determined by in vivo immunoneutralization, removal of apo A-IV from chylous lymph by immunoprecipitation, and by exogenous administration of apo A-I. Lipid-induced inhibition of gastric emptying and release of CCK will be measured in apo A-IV over-expressing and apo A-IV knockout mice. CCK secretion from STC-1 ;cells will be measured in vitro to determine that apo A-IV acts direct on endocrine cells. Intestinal vagal afferent fiber discharge will be measured in response to intestinal perfusion of lipid and exogenous administration of apo A- IV acts directly on endocrine cells. Intestinal vagal afferent fiber discharge will be measured in response to intestinal perfusion of lipid and exogenous administration of apo A-IV and determine that both of these responses are CCK-AR- dependent using the CCK-AR antagonist devazepide. A direct effect of Cck on vagal afferents innervating the gastro-duodenum will be determined by measuring calcium fluxes in response to CCK in nodose neurons in vitro. The cellular sites of expression and origins of Cck-ARs will be determined in immunohistochemical studies using antisera raised to different regions of the rat CCK-AR in tissue from intact, extrinsically denervated or capsaicin treated rats The co- localization of CCK-AR with other enteric neuropeptides, and with neuronal and endocrine CCK will be determined in double labeling experiments. The functional regulation of Cck- Ars in the stomach and duodenum will by investigated using exogenous and endogenous CCK and devazepide. These studies address sensory transduction in the gastrointestinal tract which is important in the regulation of normal digestive function. There is evidence that sensory function of the intestine is altered in pathological conditions such as inflammatory bowel disease, irritable bowel syndrome and obesity. A greater understanding of these sensory mechanisms will help in understanding the pathophysiology of these diseases.
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