Peptide YY, Glucagon-Like Peptide-1, and Neurotensin Responses to Luminal Factors in the Isolated Vascularly Perfused Rat Ileum

Abstract

Exposure of the ileum to nutrients markedly inhibits several upper gastrointestinal functions. Hormonal peptides of the ileal wall, i.e. peptide YY (PYY), glucagon-like peptide-1 (GLP-1), and neurotensin (NT), are thought to play a role in this negative feedback mechanism. The present study was conducted to comparatively assess the secretion of PYY, GLP-1, and NT upon luminal infusion of a variety of individual luminal factors in the isolated vascularly perfused rat ileum preparation. PYY, GLP-1, and NT were measured in the portal effluent with specific RIAs. Glucose (250 mM) induced a pronounced release of the three peptides, whereas a physiological concentration of 5 mM did not induce peptide secretion. Peptone (5%, wt/vol) evoked a sustained release of PYY, GLP-1, and NT. Only NT secretion was increased upon luminal administration of 100 mM sodium oleate.Short chain fatty acids (20 mM) evoked an early and transient release of the three peptides. In contrast, taurocholate (20 mM) induced a sustained release of PYY, GLP-1, and NT, but the threshold concentration for peptide release was lower for NT than for PYY or GLP-1. Cellulose or pectin (0.5%, wt/vol) did not modify peptide secretion. In conclusion, glucose and peptone are potent stimulants of PYY, GLP-1, and NT release. Only NT is released upon oleic acid stimulation. Finally, taurocholate is a potent stimulant of the release of the three peptides. Overall, PYY, GLP-1, and NT may participate cooperatively in the ileal brake. As relatively high concentrations of the various stimulants were required to elicit peptide release, it seems likely that this mechanism operates in cases of maldigestion or malabsorption. (Endocrinology 139: 3780 -3786, 1998) U NABSORBED nutrients reaching the ileum influence the functions of the upper gut to increase the efficiency of digestion and absorption. For example, unabsorbed fat or protein in the ileum delays the passage of material through the small intestine. As a delay in small bowel transit increases the contact time between luminal contents and absorptive epithelium, this mechanism may serve to increase the absorption of a meal. This negative feedback mechanism referred to as the ileal brake presumably involves hormonal intermediates. As the ileal mucosa contains several distinct populations of endocrine cells, many studies focused on the effects of the products of these cells on gastrointestinal functions. Neurotensin (NT), the major product of the so-called N cells, and peptide YY (PYY) and glucagon-like peptide 1 (GLP-1), which are cosynthesized in the so-called L cells, have been implicated in these feedback mechanisms.Circulating levels of NT, PYY, and GLP-1 rapidly increase in response to oral ingestion of a mixed meal, thus suggesting that their release is triggered in part by hormonal and/or neural signals originating from the upper small intestine. As NT, PYY, and GLP-1 are contained in open-type cells, nutrients making contact with the ileal mucosa are also capable of eliciting peptide secretion. In...

Increased plasma PYY levels following supplementation with the functional fiber PolyGlycopleX in healthy adults

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The vagus nerve, food intake and obesity

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