From gut nutrient sensing to nutrient perception: a cooperative role involving CCK and 5-HT?

Abstract

GUT-BRAIN AXIS INTERPLAY REMAINS a major question in physiology. The release of 5-HT by endocrine cells was previously demonstrated to respond to different stimuli including pressure sensors and sodium-glucose cotransporter, whereas CCK release responds to apolipoprotein A-IV and Pept1 activation. The paper from Savastano, Hayes, and Covasa in this issue of Integrative and Comparative Physiology (9) extends the release of 5-HT and 5-HT 3 receptor activation to lipid and shows cooperation between CCK and 5-HT in luminal lipid-related informations. This concept could represent a key mechanism in the understanding of the interplay between gut mechanosensitivity, gut chemosensitivity, and specific nutrient sensing, transduction, central encoding, and perception. Whether apolipoprotein A-IV or another lipid-associated signal is involved in the transduction mechanism remains to be determined. The central encoding of the 5-HT 3 and CCK1 receptors vagus-mediated mechanical and chemical-related sensory informations also represents an exciting area for future research.Understanding the mechanisms involved in gut-brain axis interplay remains a major question in physiology. It is established that intrinsic and extrinsic afferent fibers from nerves of the gastrointestinal tract continuously receive informations related to a number of mechanical and chemical stimuli applied to the mucosa of the small intestine. They transmit these informations to the enteric nervous system (ENS) and to the central nervous system (CNS), respectively. Altogether they exert feedback control of both gastrointestinal muscle contraction and intestinal secretion and also participate to the central feeling of satiation and satiety and to the control of food intake. Savastano et al. (9) show that cooperation between CCK and 5-HT in luminal lipid-related information represents an interesting contribution to the understanding of these complex mechanisms.The regulatory mechanisms involving mechanosensitivity and chemosensitivity of intrinsic and extrinsic gut afferent fibers are of particular importance since they participate, during meals, in the overall control and concomitant adaptation of food intake, meal digestion, and nutrient assimilation. They adapt food ingestion to stomach distension, regulate intestinal processes according to the entry of nutrients from the stomach, and participate in the regulation of the supply of nutrients and energy to the body. The extent of the gut mechanosensitivity and chemosensitivity has been inferred from in vivo physiological experiments in a variety of animal models and in humans. These experiments demonstrated that gastric and intestinal distension triggers the peristaltic reflex, affect gastric secretion, and induce satiation and meal termination. Similarly, luminal perfusion of the intestine with acid, carbohydrate, lipid, protein, amino acids, or high-osmolarity solutions is known to decrease gastric motility, delay gastric emptying, decrease gastric acid secretion, induce satiation or satiety, and produc...

Gp93, the Drosophila GRP94 ortholog, is required for gut epithelial homeostasis and nutrient assimilation-coupled growth control

“…These data suggest that the altered midgut function and morphology in Gp93 mutant larvae also includes disruptions in gut-specific nutrient sensing and signaling function. In mammalian systems, nutrient sensing in the gut is mediated by enteroendocrine cells, signaling via peptide hormones including 5-HT, cholecystokinin (CCK), secretin, corticotrophin-releasing factor, somatostatin, orexin, or peptide YY (Tome, 2007). The Drosophila larval midgut contains enteroendocrine cells and these cells are a significant source of peptide hormones that can be presumed to regulate appetite and digestion by similar mechanisms to those occurring in mammals (Micchelli and Perrimon, 2006; Nichols, 2007; Ohlstein and Spradling, 2006; Veenstra, 2009).…”

Gut sensing mechanisms

“…I cells are triangular, with the apical microvilli positioned to sample gut luminal contents, and the CCK secretory granules facing the base of the cell so that CCK can be released basally, away from the lumen, into either the blood or the interstitial space where surrounding cells can be stimulated. Intestinal CCK is secreted mainly in response to luminal lipid and protein (eg, apolipoprotein AIV and Pept1) [1,6,7]. In vivo studies showed that protein must be broken down into short-chain peptides and amino acids to result in the most potent CCK secretion [6].…”

The trophic effect of cholecystokinin on the pancreas declines in rats on total parenteral nutrition

“…It stimulates pancreatic secretion and induces growth of the pancreas (Ussa et al., 2008). Cholecystokinin is released into the circulation upon luminal stimulation of the intestine by factors such as protein, fatty acids, or fat (Tome, 2007). After its release, CCK stimulates pancreatic secretion.…”

“…After its release, CCK stimulates pancreatic secretion. The stimulatory effect of CCK is mediated via CCK‐1 receptors existing in the pancreas (Tome, 2007; Fan, 2008).…”