Signals Arising from the Gastrointestinal Tract that Affect Food Intake

Excess energy intake, in relation to expenditure, leads to weight gain and eventually to obesity. Obesity is rapidly increasing in Western countries and is associated with an increased risk of several diseases and a significantly higher mortality rate. Control of food intake consists of complex interplay between the peripheral body and the central nervous system. The gastrointestinal tract secretes several peptide hormones that participate in the control of feeding behaviour. The release of these peptides is controlled by energy status and nutrients. In addition to food intake, gastrointestinal peptides control digestion and gastrointestinal motility. This study investigated the effects of food components on the release of gastrointestinal peptides and their effects on food intake. Our everyday diet is rich in plant lectins, proteins with carbohydrate binding capacity. In this thesis we showed that human gallbladder contraction was effectively stimulated by red kidney bean lectin phytohaemagglutinin (PHA). Intraduodenal administration of PHA induced gallbladder contraction via a cholinergic mechanism, without affecting peripheral plasma cholecystokinin (CCK) levels. Dietary fibre is considered as a key element in a healthy diet. Postprandial glucose and insulin lowering effects of fibre have been shown to be dependent on its viscosity. In this thesis we demonstrate that viscosity also affects other postprandial gastrointestinal peptide responses and satiety. Interestingly, low-viscous oat bran beverage evoked higher satiety scores compared to otherwise similar but high-viscous beverage. This was in accordance with significantly increased releases of the hormones CCK, peptide YY (PYY) and glucagon like peptide 1 (GLP-1) as well as the more efficiently suppressed ghrelin levels after the consumption of the low-viscous beverage compared to high-viscous one. Our results indicate that the rheological properties of dietary fibre significantly affect the postprandial responses and satiety. Spices, besides giving flavour to food, also induce thermogenesis and may affect satiety. Pungent ingredients of wasabi, mustard oil and garlic are known to activate TRPA1 (transient receptor potential ankyrin 1) channels. We found TRPA1 expression in mouse and human duodenum and revealed that activation of these channels caused a robust increase in CCK secretion from the mouse intestinal neuroendocrine cell line STC-1 suggesting that these spices may improve digestion and affect satiety by stimulating CCK release. PYY, secreted from the ileum and colon, has been proposed to be a satiety peptide because it has been shown to inhibit food intake in humans and in rodents. We performed proctocolectomy in rats in order to create a surgical knock-out model for PYY. Colectomized rats were implanted with minipumps delivering PYY(3-36) or saline. In contrast to our expectations, colectomy increased rather than decreased plasma PYY levels. In spite of significantly different plasma PYY levels between the treatment groups, no difference in daily food intake or body weight gain was observed. In conclusion, this thesis shows that components in our food significantly affect gastrointestinal functions and peptide secretion. Thus by modulating the meal composition we may be able to affect food intake and satiety. National Library of Medicine classification: QU 68, QU 83, WI 102, WI 302, WK 170 Medical Subject Headings: Appetite Regulation; Cholecystokinin; Dietary Fiber; Digestive Physiology; Gallbladder Emptying; Gastric Emptying; Gastrointestinal Hormones; Ghrelin; Glucagon-Like Peptide 1; Peptide YY; Phytohemagglutinins; Plant Lectins; Transient Receptor Potential Channels