Localization of cholecystokinin receptor subtypes in the endocine pancreas

Cholecystokinin (CCK): a neuromodulator with therapeutic potential in Alzheimer's and Parkinson's disease

Cholecystokinin (CCK) is a neuropeptide modulating digestion, glucose levels, neurotransmitters and memory. Recent studies suggest that CCK exhibits neuroprotective effects in Alzheimer's disease (AD) and Parkinson's disease (PD). Thus, we review the physiological function and therapeutic potential of CCK. The neuropeptide facilitates hippocampal glutamate release and gates GABAergic basket cell activity, which improves declarative memory acquisition, but inhibits consolidation. Cortical CCK alters recognition memory and enhances audio-visual processing. By stimulating CCK-1 receptors (CCK-1Rs), sulphated CCK-8 elicits dopamine release in the substantia nigra and striatum. In the mesolimbic pathway, CCK release is triggered by dopamine and terminates reward responses via CCK-2Rs. Importantly, activation of hippocampal and nigral CCK-2Rs is neuroprotective by evoking AMPK activation, expression of mitochondrial fusion modulators and autophagy. Other benefits include vagus nerve/CCK-1R-mediated expression of brain-derived neurotrophic factor, intestinal protection and suppression of inflammation. We also discuss caveats and the therapeutic combination of CCK with other peptide hormones.

Structural insights into human brain-gut peptide cholecystokinin receptors

The intestinal hormone and neuromodulator cholecystokinin (CCK) receptors CCK1R and CCK2R act as a signaling hub in brain–gut axis, mediating digestion, emotion, and memory regulation. CCK receptors exhibit distinct preferences for ligands in different posttranslational modification (PTM) states. CCK1R couples to G_s and G_q, whereas CCK2R primarily couples to G_q. Here we report the cryo-electron microscopy (cryo-EM) structures of CCK1R–G_s signaling complexes liganded either by sulfated cholecystokinin octapeptide (CCK-8) or a CCK1R-selective small-molecule SR146131, and CCK2R–G_q complexes stabilized by either sulfated CCK-8 or a CCK2R-selective ligand gastrin-17. Our structures reveal a location-conserved yet charge-distinct pocket discriminating the effects of ligand PTM states on receptor subtype preference, the unique pocket topology underlying selectivity of SR146131 and gastrin-17, the conformational changes in receptor activation, and key residues contributing to G protein subtype specificity, providing multiple structural templates for drug design targeting the brain–gut axis.

The early story of growth hormone-releasing factor in rats, swine, and cattle

Following the discovery of the growth hormone-releasing factor from a human pancreatic tumor by the group of Guillemin at the Salk Institute in California, research on this factor has exploded. This review article is focused on the results obtained early after this discovery and summarizes the biological effects of this releasing factor on the rat digestive system development and above all on pig, steer, and gilt growth as well as on milk production in lactating sows and cows.

Pancreas—Its Functions, Disorders, and Physiological Impact on the Mammals’ Organism

This review aimed to analyze the scientific literature on pancreatic diseases (especially exocrine pancreatic insufficiency). This review also describes the correlation between the physiological fitness of the pancreas and obesity. The influence of the pancreatic exocrine function on the development of the organism of adults and adolescents was also described. The results of piglet studies available in the literature were cited as an established model used to optimize treatments for pancreatic diseases in humans. The pancreas has an exocrine and hormonal function. Consequently, it is one of the key internal organs in animals and humans. Pancreatic diseases are usually severe and particularly troublesome. A properly composed diet and taken dietary supplements significantly improve the patient’s well-being, as well as the course of the disease. Therefore, a diet and a healthy lifestyle positively affect maintaining the optimal physiological efficiency of the pancreas.

Potential Therapeutic Targeting Neurotransmitter Receptors in Diabetes

Neurotransmitters are signaling molecules secreted by neurons to coordinate communication and proper function among different sections in the central neural system (CNS) by binding with different receptors. Some neurotransmitters as well as their receptors are found in pancreatic islets and are involved in the regulation of glucose homeostasis. Neurotransmitters can act with their receptors in pancreatic islets to stimulate or inhibit the secretion of insulin (β cell), glucagon (α cell) or somatostatin (δ cell). Neurotransmitter receptors are either G-protein coupled receptors or ligand-gated channels, their effects on blood glucose are mainly decided by the number and location of them in islets. Dysfunction of neurotransmitters receptors in islets is involved in the development of β cell dysfunction and type 2 diabetes (T2D).Therapies targeting different transmitter systems have great potential in the prevention and treatment of T2D and other metabolic diseases.

Reversal of autoimmunity by mixed chimerism enables reactivation of β cells and transdifferentiation of α cells in diabetic NOD mice

Cure of autoimmune type 1 diabetes (T1D) requires both reversal of autoimmunity and regeneration or resupply of insulin-producing β cells. We have observed that combination therapy with induction of haploidentical mixed chimerism and administration of gastrin and epidermal growth factor (EGF) cures firmly established T1D. The predominant source of β cell regeneration in mice comes from reactivation of dysfunctional insulin^lo β cells and transdifferentiation of α cells. These studies have provided insights into β cell regeneration mechanisms in firmly established autoimmune T1D, in particular, reactivation of the insulin^lo β cells after reversal of autoimmunity by induction of haploidentical mixed chimerism. These studies also provide a preclinical scientific basis for the feasibility of cure of long-standing T1D in humans.

Type 1 diabetes (T1D) results from the autoimmune destruction of β cells, so cure of firmly established T1D requires both reversal of autoimmunity and restoration of β cells. It is known that β cell regeneration in nonautoimmune diabetic mice can come from differentiation of progenitors and/or transdifferentiation of α cells. However, the source of β cell regeneration in autoimmune nonobese diabetic (NOD) mice remains unclear. Here, we show that, after reversal of autoimmunity by induction of haploidentical mixed chimerism, administration of gastrin plus epidermal growth factor augments β cell regeneration and normalizes blood glucose in the firmly established diabetic NOD mice. Using transgenic NOD mice with inducible lineage-tracing markers for insulin-producing β cells, Sox9⁺ ductal progenitors, Nestin⁺ mesenchymal stem cells, and glucagon-producing α cells, we have found that both reactivation of dysfunctional low-level insulin expression (insulin^lo) β cells and neogenesis contribute to the regeneration, with the latter predominantly coming from transdifferentiation of α cells. These results indicate that, after reversal of autoimmunity, reactivation of β cells and transdifferentiation of α cells can provide sufficient new functional β cells to reach euglycemia in firmly established T1D.

Life with the pancreas: A personal experience

This review article has primary objective to summarize pancreatic research which has been done in our laboratory since 1965, the first year of the author's registration in the Ph.D. program at the University of Sherbrooke (Canada). It covers the following major topics of pancreatic physiology: controls of pancreatic adaptation to diet, control of pancreatic enzyme secretion, control of pancreatic enzyme synthesis, control of pancreatic growth, intracellular events stimulated during pancreatic growth, pancreas regeneration after pancreatitis and pancreatectomy, the pancreatic cholecystokinin receptor types 1 and 2, growth control and cell signaling in pancreatic cancer cells and finally, cystic fibrosis.

Premises for Cholecystokinin and Gastrin Peptides in Diabetes Therapy

Gastrin and cholecystokinin (CCK) are classical gastrointestinal peptide hormones. Their biogenesis, structures, and intestinal secretory patterns are well-known with the striking feature that their receptor-bound 'active sites' are highly homologous and that this structure is conserved for more than 500 million years during evolution. Consequently, gastrin and CCK are agonists for the same receptor (the CCK2 receptor). But in addition, tyrosyl O-sulphated CCK are also bound to the specific CCK1 receptor. The receptors are widely expressed in the body, including pancreatic islet-cell membranes. Moreover, CCK and gastrin peptides are at various developmental stages and diseases expressed in pancreatic islets; also in human islets. Accordingly, bioactive gastrin and CCK peptides stimulate islet-cell growth as well as insulin and glucagon secretion. In view of their insulinotropic effects, gastrin and CCK peptides have come into focus as drug targets, either alone or in combination with other insulinotropic gut hormones or growth factors. So far, modified CCK and gastrin peptides are being examined as potential drugs for therapy of type 1 as well as type 2 diabetes mellitus.

Islets from human donors with higher but not lower hemoglobin A1c levels respond to gastrin treatment in vitro

Gastrin is a peptide hormone, which in combination with other factors such as TGFα, EGF or GLP-1, is capable of increasing beta cell mass and lowering blood glucose levels in adult diabetic mice. In humans, administration of a bolus of gastrin alone induces insulin secretion suggesting that gastrin may target islet cells. However, whether gastrin alone is sufficient to exert an effect on isolated human islets has been controversial and the mechanism remained poorly understood. Therefore, in this study we started to examine the effects of gastrin alone on cultured adult human islets. Treatment of isolated human islets with gastrin I for 48 h resulted in increased expression of insulin, glucagon and somatostatin transcripts. These increases were significantly correlated with the levels of donor hemoglobin A1_c (HbA_1c) but not BMI or age. In addition, gastrin treatment resulted in increased expression of PDX1, NKX6.1, NKX2.2, MNX1 and HHEX in islets from donors with HbA_1c greater than 42 mmol/mol. The addition of YM022, an antagonist of the gastrin receptor cholecystokinin B receptor (CCKBR), together with gastrin eliminated these effects, verifying that the effects of gastrin are mediated through CCKBR.CCKBR is expressed in somatostatin-expressing delta cells in islets from all donors. However, in the islets from donors with higher HbA_1c (greater than 42 mmol/mol [6.0%]), cells triple-positive for CCKBR, somatostatin and insulin were detected, suggesting a de-differentiation or trans-differentiation of endocrine cells. Our results demonstrate a direct effect of gastrin on human islets from prediabetic or diabetic individuals that is mediated through CCKBR⁺ cells. Further, our data imply that gastrin may be a potential treatment for diabetic patients.

Emerging hormonal-based combination pharmacotherapies for the treatment of metabolic diseases

Obesity and its comorbidities, such as type 2 diabetes mellitus and cardiovascular disease, constitute growing challenges for public health and economies globally. The available treatment options for these metabolic disorders cannot reverse the disease in most individuals and have not substantially reduced disease prevalence, which underscores the unmet need for more efficacious interventions. Neurobiological resilience to energy homeostatic perturbations, combined with the heterogeneous pathophysiology of human metabolic disorders, has limited the sustainability and efficacy of current pharmacological options. Emerging insights into the molecular origins of eating behaviour, energy expenditure, dyslipidaemia and insulin resistance suggest that coordinated targeting of multiple signalling pathways is probably necessary for sizeable improvements to reverse the progression of these diseases. Accordingly, a broad set of combinatorial approaches targeting feeding circuits, energy expenditure and glucose metabolism in concert are currently being explored and developed. Notably, several classes of peptide-based multi-agonists and peptide-small molecule conjugates with superior preclinical efficacy have emerged and are currently undergoing clinical evaluation. Here, we summarize advances over the past decade in combination pharmacotherapy for the management of obesity and type 2 diabetes mellitus, exclusively focusing on large-molecule formats (notably enteroendocrine peptides and proteins) and discuss the associated therapeutic opportunities and challenges.

Expression of Gastrin Family Peptides in Pancreatic Islets and Their Role in β-Cell Function and Survival

OBJECTIVES

Modulation of cholecystokinin (CCK) receptors has been shown to influence pancreatic endocrine function.

METHODS

We assessed the impact of the CCKA and CCKB receptor modulators, (pGlu-Gln)-CCK-8 and gastrin-17, respectively, on β-cell secretory function, proliferation and apoptosis and glucose tolerance, and investigating alterations of CCK and gastrin islet expression in diabetes.

RESULTS

Initially, the presence of CCK and gastrin, and expression of their receptors were evidenced in β-cell lines and mouse islets. (pGlu-Gln)-CCK-8 and gastrin-17 stimulated insulin secretion from BRIN-BD11 and 1.1B4 β-cells, associated with no effect on membrane potential or [Ca]i. Only (pGlu-Gln)-CCK-8 possessed insulin secretory actions in isolated islets. In agreement, (pGlu-Gln)-CCK-8 improved glucose disposal and glucose-induced insulin release in mice. In addition, (pGlu-Gln)-CCK-8 evoked clear satiety effects. Interestingly, islet colocalization of CCK with glucagon was elevated in streptozotocin- and hydrocortisone-induced diabetic mice, whereas gastrin coexpression in α cells was reduced. In contrast, gastrin colocalization within β-cells was higher in diabetic mice, while CCK coexpression with insulin was decreased in insulin-deficient mice. (pGlu-Gln)-CCK-8 and gastrin-17 also augmented human and rodent β-cell proliferation and offered protection against streptozotocin-induced β-cell cytotoxicity.

CONCLUSIONS

We highlight the direct involvement of CCKA and CCKB receptors in pancreatic β-cell function and survival.

Ex vivo human pancreatic slice preparations offer a valuable model for studying pancreatic exocrine biology

A genuine understanding of human exocrine pancreas biology and pathobiology has been hampered by a lack of suitable preparations and reliance on rodent models employing dispersed acini preparations. We have developed an organotypic slice preparation of the normal portions of human pancreas obtained from cancer resections. The preparation was assessed for physiologic and pathologic responses to the cholinergic agonist carbachol (Cch) and cholecystokinin (CCK-8), including 1) amylase secretion, 2) exocytosis, 3) intracellular Ca²⁺ responses, 4) cytoplasmic autophagic vacuole formation, and 5) protease activation. Cch and CCK-8 both dose-dependently stimulated secretory responses from human pancreas slices similar to those previously observed in dispersed rodent acini. Confocal microscopy imaging showed that these responses were accounted for by efficient apical exocytosis at physiologic doses of both agonists and by apical blockade and redirection of exocytosis to the basolateral plasma membrane at supramaximal doses. The secretory responses and exocytotic events evoked by CCK-8 were mediated by CCK-A and not CCK-B receptors. Physiologic agonist doses evoked oscillatory Ca²⁺ increases across the acini. Supraphysiologic doses induced formation of cytoplasmic autophagic vacuoles and activation of proteases (trypsin, chymotrypsin). Maximal atropine pretreatment that completely blocked all the Cch-evoked responses did not affect any of the CCK-8-evoked responses, indicating that rather than acting on the nerves within the pancreas slice, CCK cellular actions directly affected human acinar cells. Human pancreas slices represent excellent preparations to examine pancreatic cell biology and pathobiology and could help screen for potential treatments for human pancreatitis.

Pancreatic β-Cells Express the Fetal Islet Hormone Gastrin in Rodent and Human Diabetes

β-Cell failure in type 2 diabetes (T2D) was recently proposed to involve dedifferentiation of β-cells and ectopic expression of other islet hormones, including somatostatin and glucagon. Here we show that gastrin, a stomach hormone typically expressed in the pancreas only during embryogenesis, is expressed in islets of diabetic rodents and humans with T2D. Although gastrin in mice is expressed in insulin⁺ cells, gastrin expression in humans with T2D occurs in both insulin⁺ and somatostatin⁺ cells. Genetic lineage tracing in mice indicates that gastrin expression is turned on in a subset of differentiated β-cells after exposure to severe hyperglycemia. Gastrin expression in adult β-cells does not involve the endocrine progenitor cell regulator neurogenin3 but requires membrane depolarization, calcium influx, and calcineurin signaling. In vivo and in vitro experiments show that gastrin expression is rapidly eliminated upon exposure of β-cells to normal glucose levels. These results reveal the fetal hormone gastrin as a novel marker for reversible human β-cell reprogramming in diabetes.

Somatostatin: One of the Rare Multifunctional Inhibitors of Mammalian Species

This review article has for major main objectives to give an overlook of the major physiological effects of somatostatin on different organs. It will cover first the general aspect of the hormone, its cDNA and its protein maturation process, as well as its characterization in various organs. This aspect will be followed by the factors involved in the control of its secretion, its intracellular mode of action, and its general action on physiological processes. Secondly, the review will focus on the pancreas, looking at its in vivo and in vitro actions with special attention on its effects on normal pancreas growth and pancreatic tumors.

β-Cell dedifferentiation, reduced duct cell plasticity, and impaired β-cell mass regeneration in middle-aged rats

Limitations in β-cell regeneration potential in middle-aged animals could contribute to the increased risk to develop diabetes associated with aging. We investigated β-cell regeneration of middle-aged Wistar rats in response to two different regenerative stimuli: partial pancreatectomy (Px + V) and gastrin administration (Px + G). Pancreatic remnants were analyzed 3 and 14 days after surgery. β-Cell mass increased in young animals after Px and was further increased after gastrin treatment. In contrast, β-cell mass did not change after Px or after gastrin treatment in middle-aged rats. β-Cell replication and individual β-cell size were similarly increased after Px in young and middle-aged animals, and β-cell apoptosis was not modified. Nuclear immunolocalization of neurog3 or nkx6.1 in regenerative duct cells, markers of duct cell plasticity, was increased in young but not in middle-aged Px rats. The pancreatic progenitor-associated transcription factors neurog3 and sox9 were upregulated in islet β-cells of middle-aged rats and further increased after Px. The percentage of chromogranin A+/hormone islet cells was significantly increased in the pancreases of middle-aged Px rats. In summary, the potential for compensatory β-cell hyperplasia and hypertrophy was retained in middle-aged rats, but β-cell dedifferentiation and impaired duct cell plasticity limited β-cell regeneration.

Assessment of cholecystokinin 2 receptor (CCK2R) in neoplastic tissue

The expression of cholecystokinin 2 receptor (CCK2R, CCKBR or gastrin receptor) has been reported on a diverse range of cancers such as colorectal, liver, lung, pancreatic, ovarian, stomach, thyroid and numerous neuroendocrine/carcinoid tumors. Some cancers of the colorectum, lung, pancreas and thyroid have been shown to overexpress CCK2R in relation to normal matched tissues of the same organ. This reported overexpression has led to the development of a number of CCK2R-ligand targeted imaging and therapeutic agents. However, no comprehensive study comparing the expression of CCK2R in multiple cancers to multiple normal tissues has been performed. Herein, we report the immunohistochemical analysis of cancer samples from gastrointestinal stromal tumor (GIST), hepatocellular carcinoma (HCC), non-small cell lung cancer (NSCLC), pancreatic adenocarcinoma, and thyroid cancer against multiple normal tissue samples from esophagus, liver, lung, pancreas, stomach, spleen and thyroid. These results show that CCK2R expression is present in nearly all cancer and normal samples tested and that none of the cancer samples had expression that was statistically greater than that of all of the normal samples.

Glucagon-like peptide-1 and cholecystokinin production and signaling in the pancreatic islet as an adaptive response to obesity

Precise control of blood glucose is dependent on adequate β‐cell mass and function. Thus, reductions in β‐cell mass and function lead to insufficient insulin production to meet demand, and result in diabetes. Recent evidence suggests that paracrine signaling in the islet might be important in obesity, and disruption of this signaling could play a role in the pathogenesis of diabetes. For example, we recently discovered a novel islet incretin axis where glucagon‐like peptide‐1 regulates β‐cell production of another classic gut hormone, cholecystokinin. This axis is stimulated by obesity, and plays a role in enhancing β‐cell survival. In the present review, we place our observations in the wider context of the literature on incretin regulation in the islet, and discuss the potential for therapeutic targeting of these pathways.

Cholecystokinin expression in the β-cell leads to increased β-cell area in aged mice and protects from streptozotocin-induced diabetes and apoptosis

Cholecystokinin (CCK) is a peptide hormone produced in the gut and brain with beneficial effects on digestion, satiety, and insulin secretion. CCK is also expressed in pancreatic β-cells, but only in models of obesity and insulin resistance. Whole body deletion of CCK in obese mice leads to reduced β-cell mass expansion and increased apoptosis. We hypothesized that islet-derived CCK is important in protection from β-cell apoptosis. To determine the specific role of β-cell-derived CCK in β-cell mass dynamics, we generated a transgenic mouse that expresses CCK in the β-cell in the lean state (MIP-CCK). Although this transgene contains the human growth hormone minigene, we saw no expression of human growth hormone protein in transgenic islets. We examined the ability of MIP-CCK mice to maintain β-cell mass when subjected to apoptotic stress, with advanced age, and after streptozotocin treatment. Aged MIP-CCK mice have increased β-cell area. MIP-CCK mice are resistant to streptozotocin-induced diabetes and exhibit reduced β-cell apoptosis. Directed CCK overexpression in cultured β-cells also protects from cytokine-induced apoptosis. We have identified an important new paracrine/autocrine effect of CCK in protection of β-cells from apoptotic stress. Understanding the role of β-cell CCK adds to the emerging knowledge of classic gut peptides in intraislet signaling. CCK receptor agonists are being investigated as therapeutics for obesity and diabetes. While these agonists clearly have beneficial effects on body weight and insulin sensitivity in peripheral tissues, they may also directly protect β-cells from apoptosis.

The anti-diabetic effects of GLP-1-gastrin dual agonist ZP3022 in ZDF rats

AIMS/HYPOTHESIS

Combination treatment with exendin-4 and gastrin has proven beneficial in treatment of diabetes and preservation of beta cell mass in diabetic mice. Here, we examined the chronic effects of a GLP-1-gastrin dual agonist ZP3022 on glycemic control and beta cell dysfunction in overtly diabetic Zucker Diabetic Fatty (ZDF) rats.

METHODS

ZDF rats aged 11 weeks were dosed s.c., b.i.d. for 8 weeks with vehicle, ZP3022, liraglutide, exendin-4, or gastrin-17 with or without exendin-4. Glycemic control was assessed by measurements of HbA1c and blood glucose levels, as well as glucose tolerance during an oral glucose tolerance test (OGTT). Beta cell dynamics were examined by morphometric analyses of beta and alpha cell fractions.

RESULTS

ZP3022 improved glycemic control as measured by terminal HbA1c levels (6.2±0.12 (high dose) vs. 7.9±0.07% (vehicle), P<0.001), as did all treatments, except gastrin-17 monotherapy. In contrast, only ZP3022, exendin-4 and combination treatment with exendin-4 and gastrin-17 significantly improved glucose tolerance and increased insulin levels during an OGTT. Moreover, only ZP3022 significantly enhanced the beta cell fraction in ZDF rats, a difference of 41%, when compared to the vehicle group (0.31±0.03 vs. 0.22±0.02%, respectively, P<0.05).

CONCLUSION

These data suggest that ZP3022 may have therapeutic potential in the prevention/delay of beta cell dysfunction in type 2 diabetes.

Interaction between the cholecystokinin and endogenous cannabinoid systems in cued fear expression and extinction retention

Post-traumatic stress disorder (PTSD) is thought to develop, in part, from improper inhibition of fear. Accordingly, one of the most effective treatment strategies for PTSD is exposure-based psychotherapy. Ideally, neuroscience would inform adjunct therapies that target the neurotransmitter systems involved in extinction processes. Separate studies have implicated the cholecystokinin (CCK) and endocannabinoid systems in fear; however, there is a high degree of anatomical colocalization between the cannabinoid 1 receptor (Cnr1) and CCK in the basolateral amygdala (BLA), a brain region critical for emotion regulation. Although most research has focused on GABA and GABAergic plasticity as the mechanism by which Cnr1 mediates fear inhibition, we hypothesize that a functional interaction between Cnr1 and CCKB receptor (CCKBR) is critical for fear extinction processes. In this study, systemic pharmacological manipulation of the cannabinoid system modulated cued fear expression in C57BL/6J mice after consolidation of auditory fear conditioning. Knockout of the CCKBR, however, had no effect on fear- or anxiety-like behaviors. Nonetheless, administration of a Cnr1 antagonist increased freezing behavior during a cued fear expression test in wild-type subjects, but had no effect on freezing behavior in CCKBR knockout littermates. In addition, we found that Cnr1-positive fibers form perisomatic clusters around CCKBR-positive cell bodies in the BLA. These CCKBR-positive cells comprise a molecularly heterogenous population of excitatory and inhibitory neurons. These findings provide novel evidence that Cnr1 contributes to cued fear expression via an interaction with the CCK system. Dysfunctional Cnr1-CCKBR interactions might contribute to the etiology of, or result from, fear-related psychiatric disease.

The novel GLP-1-gastrin dual agonist ZP3022 improves glucose homeostasis and increases β-cell mass without affecting islet number in db/db mice

Antidiabetic treatments aiming to preserve or even to increase β-cell mass are currently gaining increased interest. Here we investigated the effect of chronic treatment with the novel glucagon-like peptide-1 (GLP-1)-gastrin dual agonist ZP3022 (HGEGTFTSDLSKQMEEEAVRLFIEWLKN-8Ado-8Ado-YGWLDF-NH2) on glycemic control, β-cell mass and proliferation, and islet number. Male db/db mice were treated with ZP3022, liraglutide, or vehicle for 2, 4, or 8 weeks, with terminal assessment of hemoglobin A1c, basal blood glucose, and plasma insulin concentrations. Pancreata were removed for immunohistochemical staining and stereological quantification of β-cell mass, islet numbers, proliferation, and apoptosis. Treatment with ZP3022 or liraglutide led to a significant improvement in glycemic control. ZP3022 treatment resulted in a sustained increase in β-cell mass after 4 and 8 weeks of treatment, whereas the effect of liraglutide was transient. The expansion in β-cell mass observed in the ZP3022-treated mice appeared to be driven by increased β-cell proliferation in existing islets rather than by formation of new islets, as mean islet mass increased but the number of islets remained constant. Our data demonstrate that the GLP-1-gastrin dual agonist ZP3022 causes a sustained improvement in glycemic control accompanied by an increase in β-cell mass, increased proliferation, and increased mean islet mass. The results highlight that the GLP-1-gastrin dual agonist increases β-cell mass more than liraglutide and that dual agonists could potentially be developed into a new class of antidiabetic treatments.

An atlas and functional analysis of G-protein coupled receptors in human islets of Langerhans

G-protein coupled receptors (GPCRs) regulate hormone secretion from islets of Langerhans, and recently developed therapies for type-2 diabetes target islet GLP-1 receptors. However, the total number of GPCRs expressed by human islets, as well as their function and interactions with drugs, is poorly understood. In this review we have constructed an atlas of all GPCRs expressed by human islets: the 'islet GPCRome'. We have used this atlas to describe how islet GPCRs interact with their endogenous ligands, regulate islet hormone secretion, and interact with drugs known to target GPCRs, with a focus on drug/receptor interactions that may affect insulin secretion. The islet GPCRome consists of 293 GPCRs, a majority of which have unknown effects on insulin, glucagon and somatostatin secretion. The islet GPCRs are activated by 271 different endogenous ligands, at least 131 of which are present in islet cells. A large signalling redundancy was also found, with 119 ligands activating more than one islet receptor. Islet GPCRs are also the targets of a large number of clinically used drugs, and based on their coupling characteristics and effects on receptor signalling we identified 107 drugs predicted to stimulate and 184 drugs predicted to inhibit insulin secretion. The islet GPCRome highlights knowledge gaps in the current understanding of islet GPCR function, and identifies GPCR/ligand/drug interactions that might affect insulin secretion, which are important for understanding the metabolic side effects of drugs. This approach may aid in the design of new safer therapeutic agents with fewer detrimental effects on islet hormone secretion.

Is there adaptation of the exocrine pancreas in wild animal? The case of the Roe deer

Background

Physiology of the exocrine pancreas has been well studied in domestic and in laboratory animals as well as in humans. However, it remains quite unknown in wildlife mammals. Roe deer and cattle (including calf) belong to different families but have a common ancestor. This work aimed to evaluate in the Roe deer, the adaptation to diet of the exocrine pancreatic functions and regulations related to animal evolution and domestication.

Results

Forty bovine were distributed into 2 groups of animals either fed exclusively with a milk formula (monogastric) or fed a dry feed which allowed for rumen function to develop, they were slaughtered at 150 days of age. The 35 Roe deer were wild animals living in the temperate broadleaf and mixed forests, shot during the hunting season and classified in two groups adult and young. Immediately after death, the pancreas was removed for tissue sample collection and then analyzed. When expressed in relation to body weight, pancreas, pancreatic protein weights and enzyme activities measured were higher in Roe deer than in calf. The 1^st original feature is that in Roe deer, the very high content in pancreatic enzymes seems to be related to specific digestive products observed (proline-rich proteins largely secreted in saliva) which bind tannins, reducing their deleterious effects on protein digestion. The high chymotrypsin and elastase II quantities could allow recycling of proline-rich proteins. In contrast, domestication and rearing cattle resulted in simplified diet with well digestible components. The 2^nd feature is that in wild animal, both receptor subtypes of the CCK/gastrin family peptides were present in the pancreas as in calf, although CCK-2 receptor subtype was previously identified in higher mammals.

Conclusions

Bovine species could have lost some digestive capabilities (no ingestion of great amounts of tannin-rich plants, capabilities to secrete high amounts of proline-rich proteins) compared with Roe deer species. CCK and gastrin could play an important role in the regulation of pancreatic secretion in Roe deer as in calf. This work, to the best of our knowledge is the first study which compared the Roe deer adaptation to diet with a domesticated animal largely studied.

Gastrin treatment stimulates β-cell regeneration and improves glucose tolerance in 95% pancreatectomized rats

β-Cell mass reduction is a central aspect in the development of type 1 and type 2 diabetes, and substitution or regeneration of the lost β-cells is a potentially curative treatment of diabetes. To study the effects of gastrin on β-cell mass in rats with 95% pancreatectomy (95%-Px), a model of pancreatic regeneration, rats underwent 95% Px or sham Px and were treated with [15 leu] gastrin-17 (Px+G and S+G) or vehicle (Px+V and S+V) for 15 d. In 95% Px rats, gastrin treatment reduced hyperglycemia (280 ± 52 mg vs. 436 ± 51 mg/dl, P < 0.05), and increased β-cell mass (1.15 ± 0.15 mg)) compared with vehicle-treated rats (0.67 ± 0.15 mg, P < 0.05). Gastrin treatment induced β-cell regeneration by enhancing β-cell neogenesis (increased number of extraislet β-cells in Px+G: 0.42 ± 0.05 cells/mm(2) vs. Px+V: 0.27 ± 0.07 cells/mm(2), P < 0.05, and pancreatic and duodenal homeobox 1 expression in ductal cells of Px+G: 1.21 ± 0.38% vs. Px+V: 0.23 ± 0.10%, P < 0.05) and replication (Px+G: 1.65 ± 0.26% vs. S+V: 0.64 ± 0.14%; P < 0.05). In addition, reduced β-cell apoptosis contributed to the increased β-cell mass in gastrin-treated rats (Px+G: 0.07 ± 0.02%, Px+V: 0.23 ± 0.05%; P < 0.05). Gastrin action on β-cell regeneration and survival increased β-cell mass and improved glucose tolerance in 95% Px rats, supporting a potential role of gastrin in the treatment of diabetes.

The CCK(-like) receptor in the animal kingdom: functions, evolution and structures

In this review, the cholecystokinin (CCK)(-like) receptors throughout the animal kingdom are compared on the level of physiological functions, evolutionary basis and molecular structure. In vertebrates, the CCK receptor is an important member of the G-protein coupled receptors as it is involved in the regulation of many physiological functions like satiety, gastrointestinal motility, gastric acid secretion, gall bladder contraction, pancreatic secretion, panic, anxiety and memory and learning processes. A homolog for this receptor is also found in nematodes and arthropods, called CK receptor and sulfakinin (SK) receptor, respectively. These receptors seem to have evolved from a common ancestor which is probably still closely related to the nematode CK receptor. The SK receptor is more closely related to the CCK receptor and seems to have similar functions. A molecular 3D-model for the CCK receptor type 1 has been built together with the docking of the natural ligands for the CCK and SK receptors in the CCK receptor type 1. These molecular models can help to study ligand-receptor interactions, that can in turn be useful in the development of new CCK(-like) receptor agonists and antagonists with beneficial health effects in humans or potential for pest control.

Topical cholecystokinin depresses itch-associated scratching behavior in mice

Cholecystokinin (CCK) serves as a gastrointestinal hormone and also functions as a neuropeptide in the central nervous system (CNS). CCK may be a downregulator in the CNS, as represented by its anti-opioid properties. The existence of CCK in the peripheral nervous system has also been reported. We investigated the suppressive effects of various CCKs on peripheral pruritus in mice. The clipped backs of ICR mice were painted with CCK synthetic peptides and injected intradermally with substance P (SP). The frequency of SP-induced scratching was reduced significantly by topical application of sulfated CCK8 (CCK8S) and CCK7 (CCK7S), but not by nonsulfated CCK8, CCK7, or CCK6. Dermal injection of CCK8S also suppressed the scratching frequency, suggesting that dermal cells as well as epidermal keratinocytes (KCs) are the targets of CCKs. As determined using real-time PCR, mRNA for CCK2R, one of the two types of CCK receptors, was expressed highly in mouse fetal skin-derived mast cells (FSMCs) and moderately in ICR mouse KCs. CCK8S decreased in vitro compound 48/80-promoted degranulation of FSMCs with a transient elevation of the intracellular calcium concentration. These findings suggest that CCK may exert an antipruritic effect via mast cells and that topical CCK may be clinically useful for pruritic skin disorders.

Gut-brain signalling: how lipids can trigger the gut

The gut plays a unique role in the metabolic defence against energy excess and glucose imbalance. Nutrients, such as lipids, enter the small intestine and activate sensing mechanisms to maintain energy and glucose homeostasis. It is clear that a lipid-induced gut-brain axis exists and that cholecystokinin and a neuronal network are involved, yet the underlying mechanisms in gut lipid sensing that regulate homeostasis remain largely unknown. In parallel, studies underscore the importance of enzymes involved in lipid metabolism within the brain, such as adenosine monophosphate -activated protein kinase, to maintain homeostasis. In this review, we will first examine what is known regarding the mechanisms involved in this lipid-induced gut-brain neuronal axis that regulate food intake and hepatic glucose production. We will also discuss how enzymes that govern brain lipid metabolism could potentially reveal how lipids trigger the gut, and that both the gut and brain may share common biochemical pathways to sense lipids.

Control of somatostatin (SS) secretion by CCK-1 and CCK-2 receptors' occupation in RIN-14B cells, a rat pancreatic islet cell line

OBJECTIVES

This study evaluated the role played by cholecystokinin (CCK) receptors' occupation in the control of somatostatin (SS) secretion in RIN-14B cells.

METHODS

The presence of the CCK receptors 1 and 2 was confirmed by immunofluorescence, and SS secretion was evaluated by enzyme-linked immunosorbent assay.

RESULTS

By immunofluorescence, 95% of the cell population was composed of SS cells bearing both CCK-R subtypes with 5% of beta cells (data not shown). Cerulein (Cae), a CCK-1R agonist, and pentagastrin, a CCK-2R agonist, dose-dependently increased SS release, 3-fold at 1 mumol/L Cae, 2.5-fold at 10 mumol/L pentagastrin, with occupation of both CCKRs confirmed by L-364,178 and L-365,260 inhibition of CCK receptors 1 and 2. The occupation of high-affinity CCK-1R by Cae was confirmed on SS release with JMV-180, a high-affinity CCK-1R agonist, and absence of SS release inhibition at high Cae concentration occupying the low-affinity CCK-1R. These cells release more than 60% of their SS content by constitutive secretion, confirmed by cycloheximide and brefeldin inhibiting SS synthesis and intracellular trafficking, respectively.

CONCLUSIONS

Both CCKR subtypes occupy RIN-14B cells and initiate SS secretion through constitutive secretion controlled at SS synthesis level. Somatostatin secretion via the CCK-1R occupation mobilizes its high-affinity sites.

Control of pancreatic secretion in humans

Studies on the control of pancreatic secretion in humans of all ages have been a difficult task over the years because of patients' availability and ethic committee rules. Nevertheless, studies were performed and the objectives of this review are to summarize our knowledge on the development of secretory process in newborns, on the different phases of the pancreatic responses to a meal, on the pancreatic responses to the different components of the diet, on the mechanisms involved in the control of the pancreatic responses, and finally on the receptors involved in these controls.

Gastrin, cholecystokinin and gastrointestinal tract functions in mammals

The aim of the present review is to synthesise and summarise our recent knowledge on the involvement of cholecystokinin (CCK) and gastrin peptides and their receptors in the control of digestive functions and more generally their role in the field of nutrition in mammals. First, we examined the release of these peptides from the gut, focusing on their molecular forms, the factors regulating their release and the signalling pathways mediating their effects. Second, general physiological effects of CCK and gastrin peptides are described with regard to their specific receptors and the role of CCK on vagal mucosal afferent nerve activities. Local effects of CCK and gastrin in the gut are also reported, including gut development, gastrointestinal motility and control of pancreatic functions through vagal afferent pathways, including NO. Third, some examples of the intervention of the CCK and gastrin peptides are exposed in diseases, taking into account intervention of the classical receptor subtypes (CCK1 and CCK2 receptors) and their heterodimerisation as well as CCK-C receptor subtype. Finally, applications and future challenges are suggested in the nutritional field (performances) and in therapy with regards to the molecular forms or in relation with the type of receptor as well as new techniques to be utilised in detection or in therapy of disease. In conclusion, the present review underlines recent developments in this field: CCK and gastrin peptides and their receptors are the key factor of nutritional aspects; a better understanding of the mechanisms involved may increase the efficiency of the nutritional functions and the treatment of abnormalities under pathological conditions.

Therapeutic potential for novel drugs targeting the type 1 cholecystokinin receptor

Cholecystokinin (CCK) is a physiologically important gastrointestinal and neuronal peptide hormone, with roles in stimulating gallbladder contraction, pancreatic secretion, gastrointestinal motility and satiety. CCK exerts its effects via interactions with two structurally related class I guanine nucleotide-binding protein (G protein)-coupled receptors (GPCRs), the CCK(1) receptor and the CCK(2) receptor. Here, we focus on the CCK(1) receptor, with particular relevance to the broad spectrum of signalling initiated by activation with the natural full agonist peptide ligand, CCK. Distinct ligand-binding pockets have been defined for the natural peptide ligand and for some non-peptidyl small molecule ligands. While many CCK(1) receptor ligands have been developed and have had their pharmacology well described, their clinical potential has not yet been fully explored. The case is built for the potential importance of developing more selective partial agonists and allosteric modulators of this receptor that could have important roles in the treatment of common clinical syndromes.

The role of CCK8 in the inhibition of glucose production

A recent study suggested that a rise of cholecystokinin (CCK8) in the duodenum may bring about an inhibition of hepatic glucose production. The authors made use of the pancreatic clamp technique to characterize a gut-brain-liver signal generated by CCK8 that reduces glucose output by the liver. The pancreatic clamp conditions used created a situation in which the liver was markedly deficient in both insulin and glucagon. Although the data presented indicated that CCK8 can reduce glucose production, the authors do not establish a role for this inhibition in the reduction of glucose output seen in response to feeding. It must be remembered that in response to a meal the insulin level in the hepatic sinusoids rises markedly, as does the insulin level to which the brain is exposed. It therefore seems likely that either or both of these effects will drive the suppression of glucose production rather than any effect of CCK8. The importance of the CCK8 effect needs to be determined in the presence of elevated arterial and sinusoidal insulin before any conclusion can be drawn about its relevance.

Intestinal cholecystokinin controls glucose production through a neuronal network

Cholecystokinin (CCK) is a peptide hormone that is released from the gut in response to nutrients such as lipids to lower food intake. Here we report that a primary increase of CCK-8, the biologically active form of CCK, in the duodenum lowers glucose production independent of changes in circulating insulin levels. Furthermore, we show that duodenal CCK-8 requires the activation of the gut CCK-A receptor and a gut-brain-liver neuronal axis to lower glucose production. Finally, duodenal CCK-8 fails to lower glucose production in the early onset of high-fat diet-induced insulin resistance. These findings reveal a role for gut CCK that lowers glucose production through a neuronal network and suggest that intestinal CCK resistance may contribute to hyperglycemia in response to high-fat feeding.

Hormonal control of pancreatic growth during fetal, neonatal and adult life

This review article has for major objective to summarize the old and latest developments on the hormonal controls of pancreatic growth. The article deals with hormonal controls during the fetal, neonatal and adult periods of pancreas development, growth and regeneration. During the fetal period, comparisons were made between studies performed with pancreatic explants and those designed in vivo. After birth, the effects of glucocorticoids, thyroxine, gastrin, bombesin, secretin, cholecystokinin alone or with secretin are reported. In the adults, similar studies were reported on hormones with addition of the effects of neuropeptides, the cell types targeted by hormones and the hormonal control after pancreatectomy and pancreatitis.

Arterial gastroduodenal infusion of cholecystokinin-33 stimulates the exocrine pancreatic enzyme release via an enteropancreatic reflex, without affecting the endocrine insulin secretion in pigs

OBJECTIVES

Cholecystokinin (CCK)-dependent exocrine pancreatic regulation seems to involve different pathways in different species. The aims were to explore the enteropancreatic reflex in the CCK-mediated regulation of the exocrine pancreas and to evaluate a possible involvement of this reflex in the endocrine insulin release.

METHODS

In anesthetized pigs, CCK-33 in increasing doses (4-130 pmol kg 10 min) was infused locally to the gastroduodenal artery, or systemically via the jugular vein. Also, a low CCK-33 dose (13 pmol kg) was injected to the duodenum/antrum area before and after a bilateral truncal vagotomy.

RESULTS

Cholecystokinin-33 in the physiological dose range 4 to 32 pmol kg 10 min increased protein and trypsin outputs after local infusion to the antral-duodenal area, whereas it had no effect after systemic infusion. Cholecystokinin-33 in the pharmacological dose range 64 to 130 pmol kg 10 min further increased the secretion after both local and systemic infusions. Only CCK-33 infusions in the pharmacological dose range were able to elevate the plasma insulin levels. Vagotomy had no effect on CCK-33-mediated stimulation of the enzyme release, whereas it had a significant effect on the plasma insulin level.

CONCLUSIONS

Cholecystokinin-33 in the physiological dose range 4 to 32 pmol kg 10 min stimulates the enzyme secretion but had no effect on the insulin release via a short enteropancreatic pathway in pigs.

Cholecystokinin and Somatostatin Negatively Affect Growth of the Somatostatin-RIN-14B Cells

With the exclusive presence of the pancreatic CCK-2 receptors on the pancreatic delta cells of six different species, this study was undertaken to determine the role of cholecystokinin and gastrin on growth of these somatostatin (SS) cells. For this study, the SS-RIN-14B cells were used in culture and their growth was evaluated by cell counting. Results. To our surprise, we established by Western blot that these RIN cells possess the two CCK receptor subtypes, CCK-1 and CCK-2. Occupation of the CCK-1 receptors by caerulein, a CCK analog, led to inhibition of cell proliferation, an effect prevented by a specific CCK-1 receptor antagonist. Occupation of the CCK-2 receptors by the gastrin agonist pentagastrin had no effect on cell growth. Proliferation was not affected by SS released from these cells but was inhibited by exogenous SS. Conclusions. Growth of the SS-RIN-14B cells can be negatively affected by occupation of their CCK-1 receptors and by exogenous somatostatin.

Negative control of human pancreatic secretion: physiological mechanisms and factors

The negative control of pancreatic exocrine secretion in man occurs during the interdigestive and postprandial periods of the digestive cycle. The physiological mechanisms involved include negative feedback mechanisms, well described and accepted in animals, and controlled by the cholecystokinin- and secretin-releasing factors of pancreatic and duodenal origin, along with the active pancreatic proteases present in the upper gut. The presence of these factors and their efficacy in humans, however, have their supporters and detractors, with a possibility for reconciliation among opponents. Besides these releasing factors, hormones, mostly from the intestine, are also involved in this inhibitory process of pancreatic secretion. Somatostatin, peptide YY, pancreatic polypeptide, glucagon, ghrelin, and leptin were described as potentially involved from studies mostly performed on animals. Finally, bile and bile salts have mixed responses on this inhibition, and their effects seem to be at the intestine level with gastrointestinal hormones involved. Future studies will have to be performed in humans to determine the presence of cholecystokinin- and secretin-releasing factors and their role. Finally, the demonstrated modulatory action of hormones and bile acids in other species needs to be confirmed in humans.

Carcinoid syndrome misdiagnosed as a malabsorptive syndrome after biliopancreatic diversion

A case is reported of a woman who developed untreatable diarrhea after a prior biliopancreatic diversion (BPD), attributed to the malabsorptive component. Abdominal ultrasound incidentally found focal liver lesions. On fine needle aspiration biopsy, atypia was found, and these hepatic lesions were resected with free margins. The specimen showed liver metastases of an aggressive malignant neuroendocrine neoplasm. The primary site was subsequently identified to be in the pancreas. The physician and surgeon must realize that non-related diseases can develop after bariatric surgery, as in the general population.

Cholecystokinin

PURPOSE OF REVIEW

The hormone cholecystokinin was discovered in 1928 because of its ability to induce gallbladder contraction. Since then, cholecystokinin has been shown to possess multiple functions in the gastrointestinal tract and brain. This review discusses several significant developments in cholecystokinin biology that show how it plays a role in gastrointestinal diseases, including control of appetite.

RECENT FINDINGS

Cholecystokinin was shown to induce satiety by interacting through CCK-1 receptors located in specialized regions of the hindbrain. Cholecystokinin also inhibits expression of orexigenic peptides in the hypothalamus and prevents stimulation of specialized neurons by ghrelin. In the pancreas, cholecystokinin increased the proliferation of insulin-producing beta cells and reduced insulin-induced hyperphagia. Elevated cholecystokinin levels decreased appetite and reduced intestinal inflammation caused by parasites and bacterial toxins.

SUMMARY

Understanding the mechanisms by which cholecystokinin regulates orexigenic pathways in the body may lead to strategies for controlling appetite-related disorders such as obesity and bulimia. The reduction of intestinal inflammation by dietary fats (by elevating cholecystokinin) suggests that the hormone plays an integrated role in regulating the ingestion and digestion of food that may be relevant to inflammatory diseases of the gastrointestinal tract.

Role of CCK/gastrin receptors in gastrointestinal/metabolic diseases and results of human studies using gastrin/CCK receptor agonists/antagonists in these diseases

In this paper, the established and possible roles of CCK1 and CCK2 receptors in gastrointestinal (GI) and metabolic diseases are reviewed and available results from human agonist/antagonist studies are discussed. While there is evidence for the involvement of CCK1R in numerous diseases including pancreatic disorders, motility disorders, tumor growth, regulation of satiety and a number of CCK-deficient states, the role of CCK1R in these conditions is not clearly defined. There are encouraging data from several clinical studies of CCK1R antagonists in some of these conditions, but their role as therapeutic agents remains unclear. The role of CCK2R in physiological (atrophic gastritis, pernicious anemia) and pathological (Zollinger-Ellison syndrome) hypergastrinemic states, its effects on the gastric mucosa (ECL cell hyperplasia, carcinoids, parietal cell mass) and its role in acid-peptic disorders are clearly defined. Furthermore, recent studies point to a possible role for CCK2R in a number of GI malignancies. Current data from human studies of CCK2R antagonists are presented and their potential role in the treatment of these conditions reviewed. Furthermore, the role of CCK2 receptors as targets for medical imaging is discussed.

Role of cholecystokinin in the gastric motor response to a meal in horses

OBJECTIVE

To measure plasma cholecystokinin (CCK) activity and the effect of a CCK-1 receptor antagonist on accommodation of the proximal portion of the stomach, and subsequent gastric emptying, in horses after ingestion of high-fat or high-carbohydrate meals.

ANIMALS

6 healthy adult horses with gastric cannulas.

PROCEDURES

In the first study, horses were offered a high-fat (8% fat) or a high-carbohydrate (3% fat) pelleted meal of identical volume, caloric density, and protein content. Related plasma CCK-like activity was measured by radioimmunoassay (RIA). In a separate experiment, a horse was fed a grain meal with corn oil and phenylalanine, and plasma CCK activity was assessed by bioassay. A second study evaluated the effect of a CCK-1 receptor antagonist, devazepide (0.1 mg/kg, IV), on gastric accommodation and emptying following a meal of grain supplemented with either corn oil (12.3% fat) or an isocaloric amount of glucose (2.9% fat). Gastric tone was measured by a barostat and emptying by the (13)C-octanoic acid breath test.

RESULTS

No plasma CCK-like activity was detected by RIA or bioassay before or after ingestion of meals. Preprandial devazepide did not alter the gastric accommodation response but did significantly shorten the gastric half-emptying time and time to peak breath (13)CO(2) content with the glucose-enriched meal.

CONCLUSIONS AND CLINICAL RELEVANCE

In horses, CCK participates in regulating the gastric motor response to a meal. Compared with other species, horses may be more responsive to carbohydrate than fat. A vagovagal reflex most likely mediates this regulation, with CCK as a paracrine intermediary at the intestinal level.

Cholecystokinin and gastrin receptors

Cholecystokinin and gastrin receptors (CCK1R and CCK2R) are G protein-coupled receptors that have been the subject of intensive research in the last 10 years with corresponding advances in the understanding of their functioning and physiology. In this review, we first describe general properties of the receptors, such as the different signaling pathways used to exert short- and long-term effects and the structural data that explain their binding properties, activation, and regulation. We then focus on peripheral cholecystokinin receptors by describing their tissue distribution and physiological actions. Finally, pathophysiological peripheral actions of cholecystokinin receptors and their relevance in clinical disorders are reviewed.

Cholecystokinin- and gastrin-induced protein and amylase secretion from the parotid gland of the anaesthetized rat

I.V. infusion of pentagastrin (20 microg/kg/h) or cholecystokinin (CCK)-8 (1 microg/kg/h) for 10 min caused secretion of salivary proteins from the parotid gland in the anaesthetized rat without any accompanying overt fluid secretion. This "occult" response was revealed by a subsequent wash-out injection of methacholine (5 microg/kg, I.V.) 10 min after the end of the infusion period (aiming at avoiding synergistic interactions). While the fluid response to methacholine was unaffected by the preceding infusion of pentagastrin and CCK-8, the output of protein increased by 147% (pentagastrin) and 74% (CCK-8) and that of amylase by 45% (CCK-8) compared to the responses to methacholine upon saline infusion. Those increases were abolished by the CCK-A receptor blocker (lorglumide), but not by the CCK-B receptor blocker (itriglumide). Evisceration, combined sympathetic and parasympathetic denervation of the glands and assay under adrenoceptor blockade excluded contribution from the gastro-intestinal tract, central or ganglionic mechanisms and circulating catecholamines to the increase in protein/amylase. Furthermore, Western blot demonstrated CCK receptors for both A and B subtypes in normal and chronically denervated glands. In the submandibular gland, both pentagastrin and CCK-8 evoked a trace secretion of saliva but, under the present experimental set-up, no statistically significant increase in protein output. Thus, in addition to the autonomic nervous system, gastrointestinal hormones may, in some types of glands, be involved in the secretion of salivary gland proteins.