Peter T. Schmidt

Ghrelin stimulates motility in the small intestine of rats through intrinsic cholinergic neurons

BACKGROUND AND PURPOSE Ghrelin is a peptide discovered in endocrine cells of the stomach. Since ghrelin mRNA expression and plasma levels are elevated in the fasting state, we investigated the effects of ghrelin on the interdigestive migrating myoelectric complex (MMC) in the small intestine in vivo and compared with motor effects of ghrelin in vitro. METHODS Sprague-Dawley rats were supplied with a venous catheter and bipolar electrodes in the duodenum and jejunum for electromyography of small intestine in awake rats. In organ baths, isometric contractions of segments of rat jejunum were studied. RESULTS Ghrelin dose-dependently shortened the MMC cycle length at all three recording points. At the duodenal site, the interval shortened from 17.2+/-2.0 to 9.9+/-0.8 min during infusion of ghrelin (1000 pmol kg(-1) min(-1)) and at the jejunal site from 17.5+/-2.2 to 10.5+/-0.8 min. Ghrelin contracted the muscle strips with a pD2 of 7.97+/-0.47. Atropine (10(-6) M) in vitro and (1 mg kg(-1)) in vivo blocked the effect of ghrelin. CONCLUSION Ghrelin stimulates interdigestive motility through cholinergic neurons. Ghrelin also stimulates motility, in vitro, suggesting that ghrelin receptors are present in the intestinal neuromuscular tissue and mediate its effects via cholinergic mechanisms.

Peripheral and central signals in the control of eating in normal, obese and binge-eating human subjects

The worldwide increase in the incidence of obesity is a consequence of a positive energy balance, with energy intake exceeding expenditure. The signalling systems that underlie appetite control are complex, and the present review highlights our current understanding of key components of these systems. The pattern of eating in obesity ranges from over-eating associated with binge-eating disorder to the absence of binge-eating. The present review also examines evidence of defects in signalling that differentiate these sub-types. The signalling network underlying hunger, satiety and metabolic status includes the hormonal signals leptin and insulin from energy stores, and cholecystokinin, glucagon-like peptide-1, ghrelin and peptide YY3-36 from the gastrointestinal tract, as well as neuronal influences via the vagus nerve from the digestive tract. This information is routed to specific nuclei of the hypothalamus and brain stem, such as the arcuate nucleus and the solitary tract nucleus respectively, which in turn activate distinct neuronal networks. Of the numerous neuropeptides in the brain, neuropeptide Y, agouti gene-related peptide and orexin stimulate appetite, while melanocortins and alpha-melanocortin-stimulating hormone are involved in satiety. Of the many gastrointestinal peptides, ghrelin is the only appetite-stimulating hormone, whereas cholecystokinin, glucagon-like peptide-1 and peptide YY3-36 promote satiety. Adipose tissue provides signals about energy storage levels to the brain through leptin, adiponectin and resistin. Binge-eating has been related to a dysfunction in the ghrelin signalling system. Moreover, changes in gastric capacity are observed, and as gastric capacity is increased, so satiety signals arising from gastric and post-gastric cues are reduced. Understanding the host of neuropeptides and peptide hormones through which hunger and satiety operate should lead to novel therapeutic approaches for obesity; potential therapeutic strategies are highlighted.

Association of TNFSF15 polymorphism with irritable bowel syndrome

Background Irritable bowel syndrome (IBS) is the most common gastrointestinal disorder, affecting more than 10% of the general population worldwide. Although a genetic component is suspected, unambiguous susceptibility genes have so far not been identified. This study tested the hypothesis that genes contributing to epithelial barrier integrity, control of mucosal immune responses and interactions with bacteria in the gut are associated with IBS. Methods Single nucleotide polymorphisms (SNPs) corresponding to top signals of association with Crohns disease at 30 known susceptibility loci were tested for their effect on IBS risk in 1992 individuals from two independent case–control cohorts from Sweden and the USA. Association tests included a conservative Bonferroni correction for multiple comparisons, and were also performed on specific subgroups of patients characterised by constipation (IBS-C), diarrhoea (IBS-D) or alternating constipation and diarrhoea (IBS-A). Results The Crohns disease risk allele rs4263839 G in the TNFSF15 gene was significantly associated with an increased risk of both IBS (p=2.2×10−5; OR 1.37) and more pronouncedly, IBS-C (p=8.7×10−7; OR 1.79) in the entire sample. Similar associations and risk effects of the same magnitude were observed in the two cohorts analysed separately. A correlation between rs4263839 genotype and TNFSF15 mRNA expression was detected both in peripheral blood and in rectal mucosal biopsies from healthy individuals (combined p=0.0033). Conclusions TNFSF15 is a susceptibility gene for IBS and IBS constipation. As TL1A, the protein encoded by TNFSF15, contributes to the modulation of inflammatory responses, the results support a role of immune activation in IBS.

Differential incretin effects of GIP and GLP-1 on gastric emptying, appetite, and insulin-glucose homeostasis

Background  Glucose‐dependent insulinotropic polypeptide (GIP) and glucagon‐like peptide‐1 (GLP‐1) are major incretins with important effects on glucoregulatory functions. The aim of this study was to investigate effects of GIP and GLP‐1 on gastric emptying and appetite after a mixed meal, and effects on insulin secretion and glucose disposal in humans.

Peripheral administration of GLP-2 to humans has no effect on gastric emptying or satiety

Glucagon-like peptide-1 (GLP-1) and glucagon-like peptide-2 (GLP-2) are secreted in parallel to the circulation after a meal. Intravenous (IV) GLP-1 has an inhibitory effect on gastric emptying, hunger and food intake in man. In rodents, central administration of GLP-2 increases satiety similar to GLP-1. The aim of the present study was to assess the effect of IV administered GLP-2 on gastric emptying and feelings of hunger in human volunteers. In eight (five men) healthy subjects (age 31.1+/-2.9 years and BMI 24.1+/-1.0 kg m(-2)), scintigraphic solid gastric emptying, hunger ratings (VAS) and plasma concentrations of GLP-2 were studied during infusion of saline or GLP-2 (0.75 and 2.25 pmol kg(-1) min(-1)) for a total of 180 min. Concentrations of GLP-2 were elevated to a maximum of 50 and 110 pmol l(-1) for 0.75 and 2.25 pmol kg(-1) min(-1) infusion of GLP-2, respectively. There was no effect of GLP-2 on either the lag phase (29.5+/-4.4, 26.0+/-5.2 and 21.2+/-3.6 min for saline, GLP-2 0.75 or 2.25 pmol kg(-1) min(-1), respectively) or the half emptying time (84.5+/-6.1, 89.5+/-17.8 and 85.0+/-7.0 min for saline, GLP-2 0.75 or 2.25 pmol kg(-1) min(-1), respectively). The change in hunger rating after the meal to 180 min was also unaffected by infusion of GLP-2. GLP-2 does not seem to mediate the ileal brake mechanism.

GLP-1 suppresses gastrointestinal motility and inhibits the migrating motor complex in healthy subjects and patients with irritable bowel syndrome

Abstract  Glucagon‐like peptide‐1 (GLP‐1) is released after food intake to act as an incretin. GLP‐1 also inhibits gastric emptying and increases satiety. In rats, GLP‐1 inhibits small bowel motility. Our aim was to study the effects of GLP‐1 on gastrointestinal motility in healthy subjects and patients with irritable bowel syndrome (IBS). Antro‐duodeno‐jejunal manometry was carried out during a 4‐h control period with saline, followed by a 4‐h period with intravenous GLP‐1 (healthy: 0.7 and 1.2 pmol kg−1 min−1 (n = 16); IBS, 1.2 and 2.5 pmol kg−1 min−1 (n = 14). Plasma was analysed for GLP‐1 and gut hormones, and gut tissue expression of GLP‐1 receptor was studied. In healthy subjects, GLP‐1 0.7 pmol kg−1 min−1 reduced the migrating motor complexes (MMCs) from a median of 2 (range 2–3) to 0.5 (0–2), and motility index from 4.9 ± 0.1 to 4.3 ± 0.3 ln ∑(mmHg*s min−1) in jejunum, while GLP‐1 1.2 pmol kg−1 min−1 diminshed MMCs from 2 (2–3) to 1.5 (1–2.5), and motility index from 5.2 ± 0.2 to 4.4 ± 0.2. In IBS patients, GLP‐1 1.2 pmol kg−1 min−1 reduced the MMCs from 2.5 (2–3.5) to 1 (0–1.5) without affecting motility index. At 2.5 pmol kg−1 min−1 GLP‐1 decreased MMCs from 2 (1.5–3) to 1 (0.5–1.5), and motility index from 5.2 ± 0.2 to 4.0 ± 0.5. Motility responses to GLP‐1 were similar in antrum and duodenum. Presence of the GLP‐1 receptor in the gut was verified by reverse transcriptase PCR. In conclusion, the gut peptide GLP‐1 decreases motility in the antro‐duodeno‐jejunal region and inhibits the MMC in healthy subjects and IBS patients.

Effect of peripherally administered ghrelin on gastric emptying and acid secretion in the rat.

Ghrelin is a gut peptide that is secreted from the stomach and stimulates food intake. There are ghrelin receptors throughout the gut and intracerebroventricular ghrelin has been shown to increase gastric acid secretion. The aim of the present study was to examine the effects of peripherally administered ghrelin on gastric emptying of a non-nutrient and nutrient liquid, as well as, basal and pentagastrin-stimulated gastric acid secretion in awake rats. In addition, gastric contractility was studied in vitro. Rats equipped with a gastric fistula were subjected to an intravenous infusion of ghrelin (10-500 pmol kg(-1) min(-1)) during saline or pentagastrin (90 pmol kg(-1) min(-1)) infusion. After administration of polyethylene glycol (PEG) 4000 with 51Cr as radioactive marker, or a liquid nutrient with (51)Cr, gastric retention was measured after a 20-min infusion of ghrelin (500 pmol kg(-1) min(-1)). In vitro isometric contractions of segments of rat gastric fundus were studied (10(-9) to 10(-6) M). Ghrelin had no effect on basal acid secretion, but at 500 pmol kg(-1) min(-1) ghrelin significantly decreased pentagastrin-stimulated acid secretion. Ghrelin had no effect on gastric emptying of the nutrient liquid, but significantly increased gastric emptying of the non-nutrient liquid. Ghrelin contracted fundus muscle strips dose-dependently (pD2 of 6.93+/-0.7). Ghrelin IV decreased plasma orexin A concentrations and increased plasma somatostatin concentrations. Plasma gastrin concentrations were unchanged during ghrelin infusion. Thus, ghrelin seems to not only effect food intake but also gastric motor and secretory function indicating a multifunctional role for ghrelin in energy homeostasis.

Substance P and neurokinin A are codistributed and colocalized in the porcine gastrointestinal tract

Immunoreactive substance P and neurokinin A were measured with radioimmunoassay in extracts of different segments of porcine gastrointestinal tract using C-terminally directed antisera. In all segments, the concentrations of substance P and neurokinin A were similar. The largest concentrations of both peptides were found in the mid-colon. By gel chromatography and reversed-phase high pressure liquid chromatography the immunoreactivity in extracts from ileum eluted as homogenous peptides at the positions of synthetic substance P and neurokinin A, respectively. No neurokinin B was found. By immunohistochemistry of porcine duodenum, jejunum, ileum and mid-colon, identical localization patterns were found for substance P and neurokinin A, and the two peptides demonstrated by double immunofluorescence to be colocalized in the enteric nervous system of the ileum. We conclude that the tachykinins substance P and neurokinin A are codistributed and colocalized in the procine gastrointestinal tract and suggest that the two peptides are produced from a common precursor, beta- and/or gamma-preprotachykinin, in the same neurons.

Germline Genetic Contributions to Risk for Esophageal Adenocarcinoma, Barrett’s Esophagus, and Gastroesophageal Reflux

BACKGROUND Esophageal adenocarcinoma (EA) is an increasingly common cancer with poor survival. Barretts esophagus (BE) is the main precursor to EA, and every year 0.12% to 0.5% of BE patients progress to EA. BE typically arises on a background of chronic gastroesophageal reflux (GERD), one of the risk factors for EA. METHODS We used genome-wide association data to investigate the genetic architecture underlying GERD, BE, and EA. We applied a method to estimate the variance explained (array heritability, h(2)g) and the genetic correlation (rg) between GERD, BE, and EA by considering all single nucleotide polymorphisms (SNPs) simultaneously. We also estimated the polygenic overlap between GERD, BE, and EA using a prediction approach. All tests were two-sided, except in the case of variance-explained estimation where one-sided tests were used. RESULTS We estimated a statistically significant genetic variance explained for BE (h(2)g = 35%; standard error [SE] = 6%; one-sided P = 1 × 10(-9)) and for EA (h(2)g = 25 %; SE = 5%; one-sided P = 2 × 10(-7)). The genetic correlation between BE and EA was found to be high (rg = 1.0; SE = 0.37). We also estimated a statistically significant polygenic overlap between BE and EA (one-sided P = 1 × 10(-6)), which suggests, together with the high genetic correlation, that shared genes underlie the development of BE and EA. Conversely, no statistically significant results were obtained for GERD. CONCLUSIONS We have demonstrated that risk to BE and EA is influenced by many germline genetic variants of small effect and that shared polygenic effects contribute to risk of these two diseases.

Exploring the genetics of irritable bowel syndrome: a GWA study in the general population and replication in multinational case-control cohorts

Objective IBS shows genetic predisposition, but adequately powered gene-hunting efforts have been scarce so far. We sought to identify true IBS genetic risk factors by means of genome-wide association (GWA) and independent replication studies. Design We conducted a GWA study (GWAS) of IBS in a general population sample of 11 326 Swedish twins. IBS cases (N=534) and asymptomatic controls (N=4932) were identified based on questionnaire data. Suggestive association signals were followed-up in 3511 individuals from six case-control cohorts. We sought genotype-gene expression correlations through single nucleotide polymorphism (SNP)-expression quantitative trait loci interactions testing, and performed in silico prediction of gene function. We compared candidate gene expression by real-time qPCR in rectal mucosal biopsies of patients with IBS and controls. Results One locus at 7p22.1, which includes the genes KDELR2 (KDEL endoplasmic reticulum protein retention receptor 2) and GRID2IP (glutamate receptor, ionotropic, delta 2 (Grid2) interacting protein), showed consistent IBS risk effects in the index GWAS and all replication cohorts and reached p=9.31×10−6 in a meta-analysis of all datasets. Several SNPs in this region are associated with cis effects on KDELR2 expression, and a trend for increased mucosal KDLER2 mRNA expression was observed in IBS cases compared with controls. Conclusions Our results demonstrate that general population-based studies combined with analyses of patient cohorts provide good opportunities for gene discovery in IBS. The 7p22.1 and other risk signals detected in this study constitute a good starting platform for hypothesis testing in future functional investigations.