Effect of CCK-1 receptor blockade on ghrelin and PYY secretion in men

Cholecystokinin (CCK), peptide YY (PYY), and ghrelin have been proposed to act as satiety hormones. CCK and PYY are stimulated during meal intake by the presence of nutrients in the small intestine, especially fat, whereas ghrelin is inhibited by eating. The sequence of events (fat intake followed by fat hydrolysis and CCK release) suggests that this process is crucial for triggering the effects. The aim of this study was therefore to investigate whether CCK mediated the effect of intraduodenal (ID) fat on ghrelin secretion and PYY release via CCK-1 receptors. Thirty-six male volunteers were studied in three consecutive, randomized, double-blind, cross-over studies: 1) 12 subjects received an ID fat infusion with or without 120 mg orlistat, an irreversible inhibitor of gastrointestinal lipases, compared with vehicle; 2) 12 subjects received ID long-chain fatty acids (LCF), ID medium-chain fatty acids (MCF), or ID vehicle; and 3) 12 subjects received ID LCF with and without the CCK-1 receptor antagonist dexloxiglumide (Dexlox) or ID vehicle plus intravenous saline (placebo). ID infusions were given for 180 min. The effects of these treatments on ghrelin concentrations and PYY release were quantified. Plasma hormone concentrations were measured in regular intervals by specific RIA systems. We found the following results. 1) ID fat induced a significant inhibition in ghrelin levels (P < 0.01) and a significant increase in PYY concentrations (P < 0.004). Inhibition of fat hydrolysis by orlistat abolished both effects. 2) LCF significantly inhibited ghrelin levels (P < 0.02) and stimulated PYY release (P < 0.008), whereas MCF were ineffective compared with controls. 3) Dexlox administration abolished the effect of LCF on ghrelin and on PYY. ID fat or LCF significantly stimulated plasma CCK (P < 0.006 and P < 0.004) compared with saline. MCF did not stimulate plasma CCK release. In summary, fat hydrolysis is essential to induce effects on ghrelin and PYY through the generation of LCF, whereas MCF are ineffective. Furthermore, LCF stimulated plasma CCK release, suggesting that peripheral CCK is the mediator of these actions. The CCK-1 receptor antagonist Dexlox abolished the effect of ID LCF, on both ghrelin and PYY. Generation of LCF through hydrolysis of fat is a critical step for fat-induced inhibition of ghrelin and stimulation of PYY in humans; the signal is mediated via CCK release and CCK-1 receptors.     

The effect of bariatric surgery on gastrointestinal and pancreatic peptide hormones

Bariatric surgery for obesity has proved to be an extremely effective method of promoting long-term weight reduction with additional beneficial metabolic effects, such as improved glucose tolerance and remission of type 2 diabetes. A range of bariatric procedures are in common use, including gastric banding, sleeve gastrectomy and the Roux-en-Y gastric bypass. Although the mechanisms underlying the efficacy of bariatric surgery are unclear, gastrointestinal and pancreatic peptides are thought to play an important role. The aim of this review is to summarise the effects of different bariatric surgery procedures upon gastrointestinal and pancreatic peptides, including ghrelin, gastrin, cholecystokinin (CCK), glucose-dependent insulinotropic hormone (GIP), glucagon-like peptide 1 (GLP-1), peptide YY (PYY), oxyntomodulin, insulin, glucagon and somatostatin.     

Short-term oral oleoyl-estrone decreases the expression of ghrelin in the rat stomach

Oleoyl-estrone (OE) mobilizes body fat and decreases food intake. The precise mechanism of its modulation of appetite is unknown. Since the effects of OE on food intake appear early, here we studied the effect of OE on the expression of gut peptides that affect short-term ingestive behavior: ghrelin, leptin, CCK, PYY, and GLP-1. Two hours after a single OE dose, adult male rats were killed and their stomach fundus and intestine sections were dissected and processed for real-time PCR amplification. Semi-quantitative estimation of gene mRNA tissue levels showed that OE markedly decreased ghrelin expression in the stomach; leptin mRNA was unchanged; CCK mRNA decreased in the proximal intestine while PYY and GLP-1 expression in the intestine was not altered. Our results indicate that the short-term decrease in food intake induced by OE may be essentially the consequence of a marked decrease in the expression of ghrelin in the stomach.     

Effect of GIP, GLP-1, insulin and gastrin on ghrelin release in the isolated rat stomach

Ghrelin release in man depends on the macronutrient composition of the test meal. The mechanisms contributing to the differential regulation are largely unknown. To elucidate their potential role, glucagon-like peptide-1 (GLP-1), gastric inhibitory polypeptide (GIP), insulin, gastrin and somatostatin were examined on isolated rat stomach ghrelin secretion, which offers the advantage of avoiding systemic interactions. Basal ghrelin secretion was in a range that did not permit to consistently evaluate inhibiting effects. Therefore, the effect of gastrointestinal hormones and insulin was analyzed during vagal prestimulation. GLP-1(7-36)amide 10(-8) and 10(-7) M decreased ghrelin secretion significantly. In contrast, GIP 10(-8) and 10(-7) M augmented not only prestimulated, but also basal ghrelin secretion (p<0.05). Insulin reduced ghrelin at 10(-10), 10(-8) and 10(-6) M (p<0.05). Both gastrin 10(-8) M and somatostatin 10(-6) M also significantly inhibited ghrelin secretion. These data demonstrate that GLP-1(7-36)amide, insulin, gastrin and somatostatin are potential candidates to contribute to the postprandially observed inhibition of ghrelin secretion with insulin being the most effective inhibitor in this isolated stomach model. GIP, on the other hand, could attenuate the postprandial decrease. Because protein-rich meals do not effectively stimulate GIP release, other as yet unknown intestinal factors must be responsible for protein-induced stimulation of ghrelin release.     

Brain-gut axis in pancreatic secretion and appetite control.

The stimulation of exocrine pancreatic secretion that has been attributed by Pavlov exclusively to various reflexes (nervism), was then found that it depend also on numerous enterohormones, especially cholecystokinin (CCK) and secretin, released by duodeno-jejunal mucosa and originally believed to act via an endocrine pathway. Recently, CCK and other enterohormones were found to stimulate the pancreas by excitation of sensory nerves and triggering vago-vagal and entero-pancreatic reflexes. Numerous neurotransmitters and neuropeptides released by enteric nervous system (ENS) of gut and pancreas have been also implicated in the regulation of exocrine pancreas. This article was designed to review the contribution of vagal nerves and entero-hormones, especially CCK and other enterohormones, involved in the control of appetitive behavior such as leptin and ghrelin and pancreatic polypeptide family (peptide YY and neuropeptide Y). Basal secretion shows periodic fluctuations with peals controlled by ENS and by motilin and Ach. Plasma ghrelin, that is considered as hunger hormone, increases under basal conditions, while plasma leptin falls to the lowest level. Postprandial pancreatic secretion, classically divided into cephalic, gastric and intestinal phases, involves predominantly CCK, which under physiological conditions acts almost entirely by activation of vago-vagal reflexes to stimulate the exocrine pancreas, being accompanied by the fall in plasma ghrelin and increase of plasma leptin, reflecting feeding behavior. We conclude that the major role in postprandial pancreatic secretion is played by vagus and gastrin in cephalic and gastric phases and by vagus in conjunction with CCK and secretin in intestinal phase. PP, PYY somatostatin, leptin and ghrelin that affect food intake appear to participate in the feedback control of postprandial pancreatic secretion via hypothalamic centers.     

A high-fat diet raises fasting plasma CCK but does not affect upper gut motility, PYY, and ghrelin, or energy intake during CCK-8 infusion in lean men

There is evidence from studies in animals that the effects of both fat and CCK on gastrointestinal function and energy intake are attenuated by consumption of a high-fat diet. In humans, the effects of exogenous CCK-8 on antropyloroduodenal motility, plasma CCK, peptide YY (PYY), and ghrelin concentrations, appetite, and energy intake are attenuated by a high-fat diet. Ten healthy lean males consumed isocaloric diets (~15,400 kJ per day), containing either 44% (high-fat, HF) or 9% (low-fat, LF) fat, for 21 days in single-blind, randomized, cross-over fashion. Immediately following each diet (i.e., on day 22), subjects received a 45-min intravenous infusion of CCK-8 (2 ng.kg(-1).min(-1)), and effects on antropyloroduodenal motility, plasma CCK, PYY, ghrelin concentrations, hunger, and fullness were determined. Thirty minutes after commencement of the infusion, subjects were offered a buffet-style meal, from which energy intake (in kilojoules) was quantified. Body weight was unaffected by the diets. Fasting CCK (P < 0.05), but not PYY and ghrelin, concentrations were greater following the HF, compared with the LF, diet. Infusion of CCK-8 stimulated pyloric pressures (P < 0.01) and suppressed antral and duodenal pressures (P < 0.05), with no difference between the diets. Energy intake also did not differ between the diets. Short-term consumption of a HF diet increases fasting plasma CCK concentrations but does not affect upper gut motility, PYY and ghrelin, or energy intake during CCK-8 infusion, in a dose of 2 ng.kg(-1).min(-1), in healthy males.     

Slower gastric emptying in high-fat diet induced obese rats is associated with attenuated plasma ghrelin and elevated plasma leptin and cholecystokinin concentrations

Gastrointestinal (GI) motility and gut hormones have been considered to be involved in the development and maintenance of obesity. Our aim was to assess the relationships between gastric emptying (GE), GI transit and gut hormones and leptin concentrations in diet-induced obese rat model. Male 6-week-old Sprague-Dawley rats were fed with a high-fat (HF) diet for 8weeks to generate diet-induced obesity (DIO) and diet resistant (DR) rats. GE, GI transit and plasma ghrelin, cholecystokinin (CCK), PYY and leptin concentrations were determined in DIO, DR and control (CON) rats. The DIO rats had slower GE, higher plasma leptin and CCK concentrations, and lower plasma ghrelin concentration compared with CON and DR rats. GE was correlated with plasma ghrelin (r=0.402, P=0.028), CCK (r=-0.518, P=0.003) and leptin concentration (r=-0.514, P=0.004). The slower GE, which can be considered as an adaptive response aimed at HF diet induced obesity, may be mediated by changes of plasma ghrelin, CCK and leptin concentrations.     

Immunohistochemical investigations of neuropeptides in the brain,corpora cardiaca,and corpora allata of an adult lepidopteran insect,Manduca sexta (L)

In the brain of adult specimens of the tobacco hornworm moth, Manduca sexta (L), cells immunoreactive for several kinds of neuropeptides were localized by means of the PAP procedure, by use of antisera raised against mammalian hormones or hormonal peptides. In contrast, no such neurosecretory cells were found in the corpora cardiaca and corpora allata (CC/CA); in the CC/CA, however, immunoreactive nerve fibres were observed, reaching these organs from the brain. The neurosecretory cells found in the brain were immunoreactive with at least one of the following mammalian antisera, namely those raised against the insulin B-chain, somatostatin, glucagon C-terminal, glucagon N-terminal, pancreatic polypeptide (PP), secretin, vasoactive intestinal polypeptide (VIP), glucose-dependent insulinotropic peptide (GIP), gastrin C-terminus, enkephalin, alpha- and beta-endorphin, Substance P, and calcitonin. No cells were immunoreactive with antisera specific for detecting neurons containing the insulin A-chain, nerve growth factor, epidermal growth factor, insulin connecting peptide (C-peptide), polypeptide YY (PYY), gastrin mid-portion (sequence 6-13), cholecystokinin (CCK) mid-portion (sequences 9-20 and 9-25), neurotensin C-terminus, bombesin, motilin, ACTH, or serotonin. All the neuropeptide-immunoreactive cells observed emitted nerve fibers passing through the brain to the CC and in some cases also to the CA. In CC these immunoreactive nerve fibers tended to accumulate near the aorta. It was speculated that neuropeptides are released into the circulating haemolymph and act as neurohormones.     

Evolutionary relationships of the gut hormones.

Peptides identical or related to mammalian gut hormones occur widely, not just in gut endocrine cells but also in central or peripheral nerves, amphibian skin glands, and a variety of invertebrate tissues. The dual distribution in brain and gut was probably already established early in the vertebrate line; representatives of the oldest vertebrate group, the cyclostomes, have cholecystokinin-like factors in gut endocrine cells and in brain. The related sequences of certain gut peptides, notably gastrin and cholecystokinin (CCK), and secretin, glucagon, vasoactive intestinal polypeptide (VIP), and gastric inhibitory peptide (GIP), indicate evolution from common ancestral molecules by gene duplication and divergence. Functionally important residues are conserved. Thus the COOH-terminal pentapeptide common to gastrin and CCK also contains their minimal active fragment. There are also evolutionary changes at the level of the target organ receptor mechanisms: these are also evolutionary changes at the level of the target organ receptor mechanisms; these are illustrated by evidence suggesting that secretin regulates the flow of pancreatic juice in mammals whereas the structurally related peptide VIP has a similar role in birds.     

The distribution of endocrine cells in the mucosa of the gastrointestinal tract of the house musk shrew,Suncus murinus (Insectivora)

Summary The distribution of endocrine cells in the gastrointestinal tract of the house musk shrew, Suncus murinus (Family Soricidae, Order Insectivora) was studied immunohistochemically. The hormones investigated were gastrin, cholecystokinin (CCK), somatostatin, secretin, glucagon, gastric inhibitory polypeptide (GIP), motilin and neurotensin. In the gastric mucosa, gastrin and somatostatin cells were only found in the pyloric regions, and no other hormonal cell-types were observed. In the intestinal mucosa, the largest number of endocrine cells belonged to the gastrin and glucagon/glicentin cell-types, whereas CCK-33/39 and secretin cells were the least numerous. Numbers of other cell-types were intermediate between these two groups. The gastrin and GIP cells were mostly localized in the proximal portion of the intestine, decreasing in number towards the distal portion. The motilin and CCK-33/39 cells were restricted to the proximal half. The glucagon/glicentin and neurotensin cells were most abundant in the middle portion. The somatostatin and secretin cells, although only present in small numbers, were randomly distributed throughout the intestine. This characteristic distribution of gastrointestinal endocrine cells is discussed in comparison with the distribution patterns of other mammals.Dr. Munemitsu Hoshino, who was Professor of the Department of Pathology and directed this study, passed away on May 23rd 1988     

Metabolomic linkage reveals functional interaction between glucose-dependent insulinotropic polypeptide and ghrelin in humans

The gastric peptide ghrelin promotes energy storage, appetite, and food intake. Nutrient intake strongly suppresses circulating ghrelin via molecular mechanisms possibly involving insulin and gastrointestinal hormones. On the basis of the growing evidence that glucose-dependent insulinotropic polypeptide (GIP) is involved in the control of fuel metabolism, we hypothesized that GIP and/or insulin, directly or via changes in plasma metabolites, might affect circulating ghrelin. Fourteen obese subjects were infused with GIP (2.0 pmol·kg(-1)·min(-1)) or placebo in the fasting state during either euglycemic hyperinsulinemic (EC) or hyperglycemic hyperinsulinemic clamps (HC). Apart from analysis of plasma ghrelin and insulin levels, GC-TOF/MS analysis was applied to create a hormone-metabolite network for each experiment. The GIP and insulin effects on circulating ghrelin were analyzed within the framework of those networks. In the HC, ghrelin levels decreased in the absence (19.2% vs. baseline, P = 0.028) as well as in the presence of GIP (33.8%, P = 0.018). Ghrelin levels were significantly lower during HC with GIP than with placebo, despite insulin levels not differing significantly. In the GIP network combining data on GIP-infusion, EC+GIP and HC+GIP experiments, ghrelin was integrated into hormone-metabolite networks through a connection to a group of long-chain fatty acids. In contrast, ghrelin was excluded from the network of experiments without GIP. GIP decreased circulating ghrelin and might have affected the ghrelin system via modification of long-chain fatty acid pools. These observations were independent of insulin and offer potential mechanistic underpinnings for the involvement of GIP in systemic control of energy metabolism.     

Synergistic action of gastrin and ghrelin on gastric acid secretion in rats

Gastrin and ghrelin are secreted from G cells and X/A-like cells in the stomach, respectively, and respective hormones stimulate gastric acid secretion by acting through histamine and the vagus nerve. In this study, we examined the relationship between gastrin, ghrelin and gastric acid secretion in rats. Intravenous (iv) administration of 3 and 10 nmol of gastrin induced transient increases of ghrelin levels within 10 min in a dose-dependent manner. Double immunostaining for ghrelin and gastrin receptor revealed that a proportion of ghrelin cells possess gastrin receptors. Although (iv) administration of gastrin or ghrelin induced significant gastric acid secretion, simultaneous treatment with both hormones resulted in a synergistic, rather than additive, increase of gastric acid secretion. This synergistic increase was not observed in vagotomized rats.These results suggest that gastrin may directly stimulate ghrelin release from the stomach, and that both hormones may increase gastric acid secretion synergistically.     

Effect of cholecystokinin, secretin, and gastric inhibitory polypeptide on insulin release from the isolated perfused rat pancreas

The actions of gastric inhibitory polypeptide (GIP) on insulin release from the isolated perfused rat pancreas were compared with those of pure secretin and cholecystokinin (CCK). At dose levels physiologically achievable for GIP (1 ng/mL perfusate), infusions of CCK stimulated significant insulin release both on a weight (1 ng/mL) and a molar (770 pg/mL) basis. Although 50% as potent as GIP on a weight basis and 43% as potent on a molar basis, the insulin response to CCK was multiphasic and sustained for the duration of the infusion. The action of CCK, like that of GIP, was glucose dependent yielding no significant insulin release at a low perfusate glucose concentration (80 mg/dL). Irrespective of perfusate glucose concentration or dose (1 or 5 ng/mL), secretin failed to stimulate significant release of insulin from the perfused pancreas. It was concluded that secretin is ineffective as an incretin and that a physiological role for CCK in an enteroinsular axis awaits accurate measurement of circulating levels of immunoreactive CCK.     

Gastrointestinal hormones and regulation of food intake.

Obesity has been described as the greatest current threat to human health. In order to design drugs to target obesity, it is essential to understand its physiology and pathophysiology. Several peptides synthesised in the gastrointestinal tract which affect food intake have been identified including ghrelin, cholecystokinin (CCK), glucagon-like peptide-1 (7-36) amide (GLP-1), oxyntomodulin, peptide YY (PYY) and pancreatic polypeptide (PP). These peptides represent potential targets for the design of anti-obesity drugs. In this article we review recent advances in our understanding of food intake by these gastrointestinal hormones.     

Vasoactive intestinal peptide receptor activity in human fetal enterocytes

Functional and specific receptors for vasoactive intestinal peptide (VIP) (determined by their capacity to bind ¹²⁵I-VIP and activate adenylate cyclase) and cyclic AMP-dependent phosphodiesterase activities were characterized in enterocytes of human fetal small intestine between 18 and 23 weeks of gestation. Half-maximal stimulation of the cyclase and inhibition of ¹²⁵I-VIP binding in membrane preparations were respectively observed at 1.4 and 5 × 10⁻¹⁰ M VIP. The peptides structurally related to VIP activated the cyclic AMP generating system at pharmacological doses (10⁻⁷M and above) in the following order of potency: VIP> PHI> GRF> secretin. Other peptides or test substances, including GIP, pancreatic glucagon, somatostatin-14, gastrin, CCK, neurotensin, pancreatic polypeptide, PYY, substance P, histamine and isoproterenol are inactive in this system, while the ubiquitous adenylate cyclase activators NaF, forskolin and prostaglandins were effective. These results, combined with the appearance of intestinal VIP in nerve fibers at 8 weeks and with the morphological and enzymatic maturation at 9–12 weeks of the intestinal mucosa, indicate that this neuropeptide may regulate either the differentiation or function of enterocytes during the early development of human intestinal mucosa.     

Immunohistochemical study of the distribution of endocrine cells in the gastrointestinal tract of the camel (Camelus bactrianus)

The regional distribution and relative frequency of endocrine cells in the gastrointestinal tract of the camel, Camelus bactrianus, were investigated using immunohistochemical methods. Ten types of immunoreactive (IR) endocrine cells were identified in this study. Among these cell types, only serotonin- and somatostatin-IR cells were detected in almost all regions of the gastrointestinal tract. Most of the cell types showed peak density in the pyloric gland region. The others showed restricted distribution: gastrin, cholecystokinin (CCK), motilin, bovine pancreatic polypeptide (BPP), and (gastric) substance P in the stomach; gastrin, CCK, BPP, gastric inhibitory polypeptide (GIP), glucagon, peptide tyrosine tyrosine (PYY) and substance P in the small intestine; and CCK, motilin, BPP, and PYY in the large intestine. Fundamentally the distribution pattern of endocrine cells in the gastrointestinal tract of the camel is similar to that of cattle. The distribution and frequency of endocrine cells in the glandular sac region are the same as those of the cardiac gland.     

Regulatory peptides in the pancreas of two species of elasmobranchs and in the Brockmann bodies of four teleost species

Summary Immunohistochemistry was used to localize regulatory peptides in endocrine cells and nerve fibres in the pancreas of two species of elasmobranchs (starry ray,Raja radiata and spiny dogfish,Squalus acanthias), and in the Brockmann bodies of four teleost species (goldfish,Carassius auratus, brown troutSalmo trutta, rainbow trout,Oncorhynchus mykiss and cod,Gadus morhua). In the elasmobranchs, the classical pancreatic hormones somatostatin, glucagon and insulin were present in endocrine cells of the islets. In addition, endocrine cells were labelled with antisera to enkephalins, FMRF-amide, gastrin/cholecystokinin-(CCK)/caerulein, neurotensin, neuropeptide Y (NPY), and peptide YY (PYY). Nerve fibres were demonstrated with antisera against bombesin, galanin and vasoactive intestinal polypeptide (VIP). These nerve fibres innervated the walls of blood vessels, in the exocrine as well as the endocrine tissue. In the four teleost species immunoreactivity to somatostatin, insulin and glucagon was intense in the Brockmann bodies. Cells were labelled with antisera to enkephalin, neurotensin, FMRFamide, gastrin/CCK/ caerulein, NPY, PYY and VIP. Only a few nerve fibres were found with antisera against dopamine--hydroxylase (DBH, cod), enkephalin (met-enkephalin-Arg-Phe, cod), bombesin (cod), gastrin/CCK/caerulein (cod) and VIP. Galanin-like-immunoreactive fibres were numerous in the Brockmann bodies of all teleosts examined. Immunoreactivity to calcitonin gene-related peptide (CGRP), substance P, tyrosine hydroxylase (TH), and phenyl-N-methyl transferase (PNMT) could not be found in any of the species studied.     

Immunohistochemical evidence of gastro-entero-pancreatic neurohormonal peptides of vertebrate type in the nervous system of the larva of a dipteran insect, the hoverfly, Eristalis aeneus

Using rabbit and guinea-pig antisera, raised against GEP neurohormonal peptides of mammalian origin, cells were observed in the brain and/or in the fused ventral ganglia of the last (fifth) larval instar of the hoverfly, Eristalis aeneus, being immunoreactive with antisera against insulin, somatostatin, glucagon, PP, secretin, gastrin/CCK/caerulein; substance P, enkephalin and endorphin. Most of these GEP neurohormonal peptides also occurred in nerve fibers. No immunoreactive cells or nerve fibers could be detected with antisera against GIP, VIP, (the central fragments of) CCK, bombesin or neurotensin. The antisera tested failed to reveal any immunoreactive cells or nerves in Weismann's ring (fused corpus allatum/corpus cardiacum and thoracic gland) or in different parts of the alimentary tract. The observations support the hypothesis that neuronal GEP hormonal peptide production in the brain is a genuinely original mechanism and the appearance of endocrine cells in the gut a later feature in evolution.     

Release of bombesin-like immunoreactivity from the isolated perfused rat stomach

In the present study the release of bombesin-like immunoreactivity (BLI), somatostatin and gastrin was determined form the isolated perfused rat stomach. Gastric inhibitory polypeptide (GIP, 2 X 10(-9) M) had no effect on BLI while stimulating somatostatin and gastrin release. In these experiments the luminal pH of the stomach was kept at pH 7. Reduction of the luminal pH to 2 resulted in an inhibition of BLI secretion by GIP while gastrin release was abolished and somatostatin remained unaffected compared to luminal pH 7. Acetylcholine (10(-6) and 2 X 10(-6) M) elicited a dose-dependent stimulation of BLI secretion while gastrin was stimulated and somatostatin secretion suppressed independent of the administered dose. The present data demonstrate that release of bombesin-like immunoreactivity can be modulated by intestinal hormones and neurotransmitters and is integrated into the complex system of gastrointestinal neuroendocrine regulation.