1
|
Martínez-Herrero S, Martínez A. Adrenomedullin: Not Just Another Gastrointestinal Peptide. Biomolecules 2022; 12:biom12020156. [PMID: 35204657 PMCID: PMC8961556 DOI: 10.3390/biom12020156] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2021] [Revised: 01/14/2022] [Accepted: 01/15/2022] [Indexed: 12/11/2022] Open
Abstract
Adrenomedullin (AM) and proadrenomedullin N-terminal 20 peptide (PAMP) are two bioactive peptides derived from the same precursor with several biological functions including vasodilation, angiogenesis, or anti-inflammation, among others. AM and PAMP are widely expressed throughout the gastrointestinal (GI) tract where they behave as GI hormones, regulating numerous physiological processes such as gastric emptying, gastric acid release, insulin secretion, bowel movements, or intestinal barrier function. Furthermore, it has been recently demonstrated that AM/PAMP have an impact on gut microbiome composition, inhibiting the growth of bacteria related with disease and increasing the number of beneficial bacteria such as Lactobacillus or Bifidobacterium. Due to their wide functions in the GI tract, AM and PAMP are involved in several digestive pathologies such as peptic ulcer, diabetes, colon cancer, or inflammatory bowel disease (IBD). AM is a key protective factor in IBD onset and development, as it regulates cytokine production in the intestinal mucosa, improves vascular and lymphatic regeneration and function and mucosal epithelial repair, and promotes a beneficial gut microbiome composition. AM and PAMP are relevant GI hormones that can be targeted to develop novel therapeutic agents for IBD, other GI disorders, or microbiome-related pathologies.
Collapse
|
2
|
Vázquez R, Riveiro ME, Berenguer-Daizé C, O'Kane A, Gormley J, Touzelet O, Rezai K, Bekradda M, Ouafik L. Targeting Adrenomedullin in Oncology: A Feasible Strategy With Potential as Much More Than an Alternative Anti-Angiogenic Therapy. Front Oncol 2021; 10:589218. [PMID: 33489885 PMCID: PMC7815935 DOI: 10.3389/fonc.2020.589218] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2020] [Accepted: 11/02/2020] [Indexed: 12/18/2022] Open
Abstract
The development, maintenance and metastasis of solid tumors are highly dependent on the formation of blood and lymphatic vessels from pre-existing ones through a series of processes that are respectively known as angiogenesis and lymphangiogenesis. Both are mediated by specific growth-stimulating molecules, such as the vascular endothelial growth factor (VEGF) and adrenomedullin (AM), secreted by diverse cell types which involve not only the cancerogenic ones, but also those constituting the tumor stroma (i.e., macrophages, pericytes, fibroblasts, and endothelial cells). In this sense, anti-angiogenic therapy represents a clinically-validated strategy in oncology. Current therapeutic approaches are mainly based on VEGF-targeting agents, which, unfortunately, are usually limited by toxicity and/or tumor-acquired resistance. AM is a ubiquitous peptide hormone mainly secreted in the endothelium with an important involvement in blood vessel development and cardiovascular homeostasis. In this review, we will introduce the state-of-the-art in terms of AM physiology, while putting a special focus on its pro-tumorigenic role, and discuss its potential as a therapeutic target in oncology. A large amount of research has evidenced AM overexpression in a vast majority of solid tumors and a correlation between AM levels and disease stage, progression and/or vascular density has been observed. The analysis presented here indicates that the involvement of AM in the pathogenesis of cancer arises from: 1) direct promotion of cell proliferation and survival; 2) increased vascularization and the subsequent supply of nutrients and oxygen to the tumor; 3) and/or alteration of the cell phenotype into a more aggressive one. Furthermore, we have performed a deep scrutiny of the pathophysiological prominence of each of the AM receptors (AM1 and AM2) in different cancers, highlighting their differential locations and functions, as well as regulatory mechanisms. From the therapeutic point of view, we summarize here an exhaustive series of preclinical studies showing a reduction of tumor angiogenesis, metastasis and growth following treatment with AM-neutralizing antibodies, AM receptor antagonists, or AM receptor interference. Anti-AM therapy is a promising strategy to be explored in oncology, not only as an anti-angiogenic alternative in the context of acquired resistance to VEGF treatment, but also as a potential anti-metastatic approach.
Collapse
Affiliation(s)
- Ramiro Vázquez
- Preclinical Department, Early Drug Development Group (E2DG), Boulogne-Billancourt, France.,Center for Genomic Science of IIT@SEMM, Fondazione Istituto Italiano di Tecnologia (IIT), Milan, Italy
| | - Maria E Riveiro
- Preclinical Department, Early Drug Development Group (E2DG), Boulogne-Billancourt, France
| | | | - Anthony O'Kane
- Discovery and Scientific Affairs Department, Fusion Antibodies plc., Belfast, United Kingdom
| | - Julie Gormley
- Discovery and Scientific Affairs Department, Fusion Antibodies plc., Belfast, United Kingdom
| | - Olivier Touzelet
- Discovery and Scientific Affairs Department, Fusion Antibodies plc., Belfast, United Kingdom
| | - Keyvan Rezai
- Department of Radio-Pharmacology, Institute Curie-René Huguenin Hospital, Saint-Cloud, France
| | - Mohamed Bekradda
- Preclinical Department, Early Drug Development Group (E2DG), Boulogne-Billancourt, France
| | - L'Houcine Ouafik
- Aix Marseille University, CNRS, INP, Institute of NeuroPhysiopathology, Marseille, France.,APHM, CHU Nord, Service de Transfert d'Oncologie Biologique, Marseille, France
| |
Collapse
|
3
|
Abstract
Gastric acid secretion (i) facilitates digestion of protein as well as absorption of micronutrients and certain medications, (ii) kills ingested microorganisms, including Helicobacter pylori, and (iii) prevents bacterial overgrowth and enteric infection. The principal regulators of acid secretion are the gastric peptides gastrin and somatostatin. Gastrin, the major hormonal stimulant for acid secretion, is synthesized in pyloric mucosal G cells as a 101-amino acid precursor (preprogastrin) that is processed to yield biologically active amidated gastrin-17 and gastrin-34. The C-terminal active site of gastrin (Trp-Met-Asp-Phe-NH2 ) binds to gastrin/CCK2 receptors on parietal and, more importantly, histamine-containing enterochromaffin-like (ECL) cells, located in oxyntic mucosa, to induce acid secretion. Histamine diffuses to the neighboring parietal cells where it binds to histamine H2 -receptors coupled to hydrochloric acid secretion. Gastrin is also a trophic hormone that maintains the integrity of gastric mucosa, induces proliferation of parietal and ECL cells, and is thought to play a role in carcinogenesis. Somatostatin, present in D cells of the gastric pyloric and oxyntic mucosa, is the main inhibitor of acid secretion, particularly during the interdigestive period. Somatostatin exerts a tonic paracrine restraint on gastrin secretion from G cells, histamine secretion from ECL cells, and acid secretion from parietal cells. Removal of this restraint, for example by activation of cholinergic neurons during ingestion of food, initiates and maximizes acid secretion. Knowledge regarding the structure and function of gastrin, somatostatin, and their respective receptors is providing novel avenues to better diagnose and manage acid-peptic disorders and certain cancers. Published 2020. Compr Physiol 10:197-228, 2020.
Collapse
Affiliation(s)
- Mitchell L Schubert
- Division of Gastroenterology, Department of Medicine, Virginia Commonwealth University Health System, Richmond, Virginia, USA.,Hunter Holmes McGuire Veterans Affairs Medical Center, Richmond, Virginia, USA
| | - Jens F Rehfeld
- Department of Clinical Biochemistry, Rigshospitalet, University of Copenhagen, Copenhagen, Denmark
| |
Collapse
|
4
|
Martínez-Herrero S, Martínez A. Adrenomedullin regulates intestinal physiology and pathophysiology. Domest Anim Endocrinol 2016; 56 Suppl:S66-83. [PMID: 27345325 DOI: 10.1016/j.domaniend.2016.02.004] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/25/2015] [Revised: 02/11/2016] [Accepted: 02/15/2016] [Indexed: 02/08/2023]
Abstract
Adrenomedullin (AM) and proadrenomedullin N-terminal 20 peptide (PAMP) are 2 biologically active peptides produced by the same gene, ADM, with ubiquitous distribution and many physiological functions. Adrenomedullin is composed of 52 amino acids, has an internal molecular ring composed by 6 amino acids and a disulfide bond, and shares structural similarities with calcitonin gene-related peptide, amylin, and intermedin. The AM receptor consists of a 7-transmembrane domain protein called calcitonin receptor-like receptor in combination with a single transmembrane domain protein known as receptor activity-modifying protein. Using morphologic techniques, it has been shown that AM and PAMP are expressed throughout the gastrointestinal tract, being specially abundant in the neuroendocrine cells of the gastrointestinal mucosa; in the enterochromaffin-like and chief cells of the gastric fundus; and in the submucosa of the duodenum, ileum, and colon. This wide distribution in the gastrointestinal tract suggests that AM and PAMP may act as gut hormones regulating many physiological and pathologic conditions. To date, it has been proven that AM and PAMP act as autocrine/paracrine growth factors in the gastrointestinal epithelium, play key roles in the protection of gastric mucosa from various kinds of injury, and accelerate healing in diseases such as gastric ulcer and inflammatory bowel diseases. In addition, both peptides are potent inhibitors of gastric acid secretion and gastric emptying; they regulate the active transport of sugars in the intestine, regulate water and ion transport in the colon, modulate colonic bowel movements and small-intestine motility, improve endothelial barrier function, and stabilize circulatory function during gastrointestinal inflammation. Furthermore, AM and PAMP are antimicrobial peptides, and they contribute to the mucosal host defense system by regulating gut microbiota. To get a formal demonstration of the effects that endogenous AM and PAMP may have in gut microbiota, we developed an inducible knockout of the ADM gene. Using this model, we have shown, for the first time, that lack of AM/PAMP leads to changes in gut microbiota composition in mice. Further studies are needed to investigate whether this lack of AM/PAMP may have an impact in the development and/or progression of intestinal diseases through their effect on microbiota composition.
Collapse
Affiliation(s)
- S Martínez-Herrero
- Oncology Area, Center for Biomedical Research of La Rioja (CIBIR), Logroño, La Rioja 26006, Spain
| | - A Martínez
- Oncology Area, Center for Biomedical Research of La Rioja (CIBIR), Logroño, La Rioja 26006, Spain.
| |
Collapse
|
5
|
Larráyoz IM, Martínez-Herrero S, García-Sanmartín J, Ochoa-Callejero L, Martínez A. Adrenomedullin and tumour microenvironment. J Transl Med 2014; 12:339. [PMID: 25475159 PMCID: PMC4272513 DOI: 10.1186/s12967-014-0339-2] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2014] [Accepted: 11/21/2014] [Indexed: 01/03/2023] Open
Abstract
Adrenomedullin (AM) is a regulatory peptide whose involvement in tumour progression is becoming more relevant with recent studies. AM is produced and secreted by the tumour cells but also by numerous stromal cells including macrophages, mast cells, endothelial cells, and vascular smooth muscle cells. Most cancer patients present high levels of circulating AM and in some cases these higher levels correlate with a worst prognosis. In some cases it has been shown that the high AM levels return to normal following surgical removal of the tumour, thus indicating the tumour as the source of this excessive production of AM. Expression of this peptide is a good investment for the tumour cell since AM acts as an autocrine/paracrine growth factor, prevents apoptosis-mediated cell death, increases tumour cell motility and metastasis, induces angiogenesis, and blocks immunosurveillance by inhibiting the immune system. In addition, AM expression gets rapidly activated by hypoxia through a HIF-1α mediated mechanism, thus characterizing AM as a major survival factor for tumour cells. Accordingly, a number of studies have shown that inhibition of this peptide or its receptors results in a significant reduction in tumour progression. In conclusion, AM is a great target for drug development and new drugs interfering with this system are being developed.
Collapse
Affiliation(s)
- Ignacio M Larráyoz
- Oncology Area, Center for Biomedical Research of La Rioja CIBIR, C/Piqueras 98, Logroño, 26006, Spain.
| | - Sonia Martínez-Herrero
- Oncology Area, Center for Biomedical Research of La Rioja CIBIR, C/Piqueras 98, Logroño, 26006, Spain.
| | - Josune García-Sanmartín
- Oncology Area, Center for Biomedical Research of La Rioja CIBIR, C/Piqueras 98, Logroño, 26006, Spain.
| | - Laura Ochoa-Callejero
- Oncology Area, Center for Biomedical Research of La Rioja CIBIR, C/Piqueras 98, Logroño, 26006, Spain.
| | - Alfredo Martínez
- Oncology Area, Center for Biomedical Research of La Rioja CIBIR, C/Piqueras 98, Logroño, 26006, Spain.
| |
Collapse
|
6
|
Martínez-Herrero S, Larráyoz IM, Ochoa-Callejero L, García-Sanmartín J, Martínez A. Adrenomedullin as a growth and cell fate regulatory factor for adult neural stem cells. Stem Cells Int 2012; 2012:804717. [PMID: 23049570 PMCID: PMC3462413 DOI: 10.1155/2012/804717] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2012] [Revised: 08/16/2012] [Accepted: 08/21/2012] [Indexed: 01/10/2023] Open
Abstract
The use of stem cells as a strategy for tissue repair and regeneration is one of the biomedical research areas that has attracted more interest in the past few years. Despite the classic belief that the central nervous system (CNS) was immutable, now it is well known that cell turnover occurs in the mature CNS. Postnatal neurogenesis is subjected to tight regulation by many growth factors, cell signals, and transcription factors. An emerging molecule involved in this process is adrenomedullin (AM). AM, a 52-amino acid peptide which exerts a plethora of physiological functions, acts as a growth and cell fate regulatory factor for adult neural stem and progenitor cells. AM regulates the proliferation rate and the differentiation into neurons, astrocytes, and oligodendrocytes of stem/progenitor cells, probably through the PI3K/Akt pathway. The active peptides derived from the AM gene are able to regulate the cytoskeleton dynamics, which is extremely important for mature neural cell morphogenesis. In addition, a defective cytoskeleton may impair cell cycle and migration, so AM may contribute to neural stem cell growth regulation by allowing cells to pass through mitosis. Regulation of AM levels may contribute to program stem cells for their use in medical therapies.
Collapse
Affiliation(s)
| | - Ignacio M. Larráyoz
- Oncology Area, Center for Biomedical Research of La Rioja (CIBIR), 26006 Logroño, Spain
| | - Laura Ochoa-Callejero
- Oncology Area, Center for Biomedical Research of La Rioja (CIBIR), 26006 Logroño, Spain
| | | | - Alfredo Martínez
- Oncology Area, Center for Biomedical Research of La Rioja (CIBIR), 26006 Logroño, Spain
| |
Collapse
|
7
|
Gaisano HY, Macdonald PE, Vranic M. Glucagon secretion and signaling in the development of diabetes. Front Physiol 2012; 3:349. [PMID: 22969729 PMCID: PMC3432929 DOI: 10.3389/fphys.2012.00349] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2012] [Accepted: 08/10/2012] [Indexed: 12/19/2022] Open
Abstract
Normal release of glucagon from pancreatic islet α-cells promotes glucose mobilization, which counteracts the hypoglycemic actions of insulin, thereby ensuring glucose homeostasis. In treatment of diabetes aimed at rigorously reducing hyperglycemia to avoid chronic complications, the resulting hypoglycemia triggering glucagon release from α-cells is frequently impaired, with ensuing hypoglycemic complications. This review integrates the physiology of glucagon secretion regulating glucose homeostasis in vivo to single α-cell signaling, and how both become perturbed in diabetes. α-cells within the social milieu of the islet micro-organ are regulated not only by intrinsic signaling events but also by paracrine regulation, particularly by adjacent insulin-secreting β-cells and somatostatin-secreting δ-cells. We discuss the intrinsic α-cell signaling events, including glucose sensing and ion channel regulation leading to glucagon secretion. We then discuss the complex crosstalk between the islet cells and the breakdown of this crosstalk in diabetes contributing to the dysregulated glucagon secretion. Whereas, there are many secretory products released by β- and δ-cells that become deficient or excess in diabetes, we discuss the major ones, including the better known insulin and lesser known somatostatin, which act as putative paracrine on/off switches that very finely regulate α-cell secretory responses in health and diabetes. Of note in several type 1 diabetes (T1D) rodent models, blockade of excess somatostatin actions on α-cell could normalize glucagon secretion sufficient to attain normoglycemia in response to hypoglycemic assaults. There has been slow progress in fully elucidating the pathophysiology of the α-cell in diabetes because of the small number of α-cells within an islet and the islet mass becomes severely reduced and inflamed in diabetes. These limitations are just now being surmounted by new approaches.
Collapse
Affiliation(s)
- Herbert Y Gaisano
- Departments of Medicine and Physiology, University of Toronto Toronto, ON, Canada
| | | | | |
Collapse
|
8
|
Yue JT, Burdett E, Coy DH, Giacca A, Efendic S, Vranic M. Somatostatin receptor type 2 antagonism improves glucagon and corticosterone counterregulatory responses to hypoglycemia in streptozotocin-induced diabetic rats. Diabetes 2012; 61:197-207. [PMID: 22106159 PMCID: PMC3237655 DOI: 10.2337/db11-0690] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Diminished responsiveness to hypoglycemia contributes to defective counterregulation in diabetes. Pancreatic and/or circulating somatostatin are elevated in diabetes, which may inhibit counterregulatory hormone release during hypoglycemia. Thus, a selective somatostatin receptor type 2 antagonist (SSTR2a) should improve hormone counterregulation to hypoglycemia. Nondiabetic (N) and streptozotocin-induced diabetic (D) rats underwent 4-h infusion of saline or SSTR2a with insulin-induced hypoglycemia clamped at 2.5 ± 0.5 mmol/L. To evaluate the effect of the SSTR2a in the absence of hypoglycemia, rats underwent a 4-h infusion of saline (Ctrl:N, Ctrl:D) or SSTR2a (Ctrl:D+SSTR2a) only. The attenuated glucagon response to hypoglycemia in D (P < 0.0002) was fully restored by SSTR2a (P < 0.0001). Furthermore, the attenuated corticosterone response in D (P < 0.002) was also enhanced by SSTR2a (P < 0.05). In the absence of hypoglycemia, SSTR2a did not alter basal blood glucose levels. D exhibited 62% more pancreatic somatostatin than N after hypoglycemia. In N rats, SSTR2a did not augment the glucagon or corticosterone response to hypoglycemia. Thus, somatostatin may contribute to impaired glucagon responsiveness to hypoglycemia in diabetes. We demonstrate that SSTR2 antagonism enhances hypoglycemia-stimulated glucagon and corticosterone release in D but not in N rats. SSTR2 antagonism does not affect basal glycemia in D rats.
Collapse
Affiliation(s)
- Jessica T.Y. Yue
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
| | - Elena Burdett
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
| | - David H. Coy
- Department of Medicine, Peptide Research Laboratories, Tulane University, New Orleans, Louisiana
| | - Adria Giacca
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
- Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada
| | - Suad Efendic
- Department of Molecular Medicine and Surgery, Karolinska Institute, Stockholm, Sweden
| | - Mladen Vranic
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
- Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada
- Corresponding author: Mladen Vranic,
| |
Collapse
|
9
|
Yeung M, Treit D. The anxiolytic effects of somatostatin following intra-septal and intra-amygdalar microinfusions are reversed by the selective sst2 antagonist PRL2903. Pharmacol Biochem Behav 2011; 101:88-92. [PMID: 22210489 DOI: 10.1016/j.pbb.2011.12.012] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/02/2011] [Revised: 12/10/2011] [Accepted: 12/14/2011] [Indexed: 11/30/2022]
Abstract
Somatostatin (SST) is a polypeptide with two biological isoforms (SST14, and SST28), and five SST receptor subtypes (sst1-5). Together, they mediate a number of neural and hormonal functions. Recently, we found that intracerebroventricular (ICV), intra-amygdalar, and intra-septal microinfusions of SST14, SST28, and a selective sst2 receptor agonist L-779976 all produced anxiolytic-like effects in the elevated plus-maze, a widely used animal model of anxiety. The receptor specificity of these anxiolytic-like effects, however, has not been conclusively established. Accordingly, the anxiolytic effects of SST in the elevated plus-maze were assessed following intra-septal or intra-amygalar microinfusions of 1) SST (1.5μg per hemisphere), 2) the highly selective sst2 receptor antagonist PRL2903 (1.5μg per hemisphere), or 3) the combination of SST and PRL2903 (each 1.5μg per hemisphere). Antagonism of the anxiolytic effects of SST in the plus-maze by PRL2903 should result in open-arm exploration that is equivalent to that of 4) vehicle-injected control rats. Both intra-septal and intra-amygdalar microinfusions of SST produced anxiolytic effects in the elevated plus-maze, consistent with results found previously after ICV microinfusions (see Engin et al., 2008; Engin and Treit, 2009; Yeung et al., 2011). More importantly, infusion of PRL2903 completely reversed the anxiolytic effects of SST in both the amygdala and the septum. These results show that somatostatin's anxiolytic effects are mediated by sst2 receptors contained in the amygdala and septum of the rat brain.
Collapse
Affiliation(s)
- Michelle Yeung
- Department of Psychology, University of Alberta, P-449 Biological, Sciences Building, Edmonton, AB, Canada T6G 2E9
| | | |
Collapse
|
10
|
Chapter 15 Glucose‐Dependent Insulinotropic Polypeptide (Gastric Inhibitory Polypeptide; GIP). VITAMINS AND HORMONES 2009; 80:409-71. [DOI: 10.1016/s0083-6729(08)00615-8] [Citation(s) in RCA: 123] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
|
11
|
Abstract
Although gastric acid is not essential for life, it facilitates the digestion of protein and the absorption of iron, calcium, vitamin B(12), and thyroxin. It also prevents bacterial overgrowth and enteric infection. Gastric acid secretion must be precisely regulated, as too much acid may overwhelm mucosal defense mechanisms and lead to ulceration and maldigestion. The pathways regulating gastric acid secretion may be categorized as neural, paracrine, and hormonal; the hormonal pathways are the focus of this review. During meal ingestion, the main hormone responsible for stimulating acid secretion is gastrin, which acts primarily by releasing histamine from enterochromaffin-like cells. Ghrelin and orexin may also function as stimulatory hormones. Nutrients within the intestine, mainly lipid and protein, release peptide hormones such as cholecystokinin, secretin, neurotensin, and glucagon-like peptide, which may act in concert to inhibit acid secretion.
Collapse
Affiliation(s)
- Mitchell L Schubert
- McGuire Veterans Affairs Medical Center, Code 111N, Gastroenterology Division, 1201 Broad Rock Boulevard, Richmond, VA 23249, USA.
| |
Collapse
|
12
|
de Heer J, Rasmussen C, Coy DH, Holst JJ. Glucagon-like peptide-1, but not glucose-dependent insulinotropic peptide, inhibits glucagon secretion via somatostatin (receptor subtype 2) in the perfused rat pancreas. Diabetologia 2008; 51:2263-70. [PMID: 18795252 DOI: 10.1007/s00125-008-1149-y] [Citation(s) in RCA: 170] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/23/2008] [Accepted: 08/07/2008] [Indexed: 10/21/2022]
Abstract
AIMS/HYPOTHESIS The glucose-lowering effect of glucagon-like peptide-1 (GLP-1) is based not only upon its potent insulinotropic actions but also on its ability to restrain glucagon secretion. Surprisingly, the closely related glucose-dependent insulinotropic peptide (GIP) stimulates glucagon release. We examined whether the islet hormone somatostatin, which strongly inhibits glucagon secretion, is involved in this divergent behaviour. METHODS At 1.5 mmol/l glucose and therefore minimal insulin secretion, the glucagon, insulin and somatostatin responses to 20 mmol/l glucose, GLP-1, GIP and somatostatin were studied in the presence of a high-affinity monoclonal somatostatin antibody and of a highly specific somatostatin receptor subtype 2 (SSTR2) antagonist (PRL-2903) in the isolated perfused rat pancreas. RESULTS In control experiments, GLP-1 at 1 and 10 nmol/l reduced glucagon secretion significantly to 59.0 +/- 6.3% (p < 0.004; n = 5; SSTR2 series; each vs pre-infusion level) and to 48.0 +/- 2.6% (p < 0.001; n = 6; somatostatin antibody series) respectively. During somatostatin antibody administration, GLP-1 still inhibited glucagon secretion significantly, but the effect was less pronounced than in control experiments (p < 0.018). Co-infusion of the SSTR2 antagonist completely abolished the GLP-1-induced suppression of glucagon secretion. In contrast, neither the GIP-induced stimulation of glucagon release nor its inhibition by 20 mmol/l glucose was altered by somatostatin antibody or SSTR2 antagonist administration. CONCLUSIONS/INTERPRETATION We conclude that GLP-1 is capable of inhibiting glucagon secretion even in the absence of secretory products from the beta cell. It is highly likely that this is mediated via somatostatin interacting with SSTR2 on rat alpha cells. In contrast, GIP and glucose seem to influence the alpha cell independently of somatostatin secretion.
Collapse
Affiliation(s)
- J de Heer
- Department of Biomedical Sciences, The Panum Institute, University of Copenhagen, Blegdamsvej 3, DK-2200, Copenhagen N, Denmark
| | | | | | | |
Collapse
|
13
|
Schubert ML, Peura DA. Control of gastric acid secretion in health and disease. Gastroenterology 2008; 134:1842-60. [PMID: 18474247 DOI: 10.1053/j.gastro.2008.05.021] [Citation(s) in RCA: 254] [Impact Index Per Article: 15.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/06/2008] [Accepted: 04/28/2008] [Indexed: 12/16/2022]
Abstract
Recent milestones in the understanding of gastric acid secretion and treatment of acid-peptic disorders include the (1) discovery of histamine H(2)-receptors and development of histamine H(2)-receptor antagonists, (2) identification of H(+)K(+)-ATPase as the parietal cell proton pump and development of proton pump inhibitors, and (3) identification of Helicobacter pylori as the major cause of duodenal ulcer and development of effective eradication regimens. This review emphasizes the importance and relevance of gastric acid secretion and its regulation in health and disease. We review the physiology and pathophysiology of acid secretion as well as evidence regarding its inhibition in the management of acid-related clinical conditions.
Collapse
Affiliation(s)
- Mitchell L Schubert
- Department of Medicine, Division of Gastroenterology, Virginia Commonwealth University's Medical College of Virginia, McGuire Veterans Affairs Medical Center, Richmond, Virginia 23249, USA.
| | | |
Collapse
|
14
|
Strowski MZ, Blake AD. Function and expression of somatostatin receptors of the endocrine pancreas. Mol Cell Endocrinol 2008; 286:169-79. [PMID: 18375050 DOI: 10.1016/j.mce.2008.02.007] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/31/2007] [Revised: 02/03/2008] [Accepted: 02/12/2008] [Indexed: 01/26/2023]
Abstract
Somatostatin (SST) regulates multiple biological processes via five genetically distinct, G-protein coupled receptors. Clinical interest in therapy for neuroendocrine and metabolic disorders has resulted in the development of new tools for exploring the function of somatostatin receptors (SSTRs). The development of highly SSTR-selective agonists and antagonists, animal models with the deletion of individual SSTRs, as well as SSTR-specific antibodies have all been utilized in delineating SSTR functions. In the pancreas, SST is a potent regulator of insulin and glucagon secretion. Indeed, the inappropriate regulation of pancreatic A- and B-cell function in metabolic diseases provides an impetus to evaluate the SSTRs as therapeutic targets. By combining the results obtained from molecular biology, pharmacology and immunochemical studies the current review provides a summary of important recent developments which have extended our knowledge of SST actions in the endocrine pancreas.
Collapse
Affiliation(s)
- Mathias Z Strowski
- Medizinische Klinik mit Schwerpunkt Hepatologie und Gastroenterologie, Charité-Universitätsmedizin Berlin, Berlin, Germany.
| | | |
Collapse
|
15
|
Isbil-Buyukcoskun N, Gulec G. Investigation of the mechanisms involved in the central effects of glucagon-like peptide-1 on ethanol-induced gastric mucosal lesions. ACTA ACUST UNITED AC 2005; 128:57-62. [PMID: 15721488 DOI: 10.1016/j.regpep.2004.12.019] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2004] [Revised: 11/29/2004] [Accepted: 12/11/2004] [Indexed: 10/25/2022]
Abstract
The aim of this study was to investigate the effects of intracerebroventricularly injected glucagon-like peptide-1 (GLP-1) on ethanol-induced gastric mucosal damage and to elucidate the mechanisms involved. Absolute ethanol was administered through an orogastric cannula 5 min before GLP-1 (1 microg/10 microl) injection. One hour later, the rats were decapitated, their stomachs were removed and scored for mucosal damage. GLP-1 inhibited the ethanol-induced gastric mucosal damage by 92%. Centrally injected atropine sulphate, a muscarinic receptor antagonist (5 microg/10 microl), prevented the gastroprotective effect of GLP-1, while mecamylamine, a nicotinic receptor antagonist (25 microg/10 microl), was ineffective. Peripherally injected atropine methyl nitrate (1 mg/kg) did not change the effect of GLP-1, but mecamylamine (5 mg/kg) blocked it. Cysteamine, a somatostatin depletor (280 mg/kg, s.c.), did not affect the protective activity of GLP-1, while inhibition of nitric oxide (NO) synthesis by L-NAME (3 mg/kg, i.v.) significantly abolished the protective effect of GLP-1 on ethanol-induced gastric mucosal lesions. We conclude that central muscarinic and peripheral nicotinic cholinergic receptors and NO, but not somatostatin, contribute to the protective effect of intracerebroventricularly injected GLP-1 on ethanol-induced gastric mucosal damage.
Collapse
|
16
|
Fykse V, Coy DH, Waldum HL, Sandvik AK. Somatostatin-receptor 2 (sst2)-mediated effects of endogenous somatostatin on exocrine and endocrine secretion of the rat stomach. Br J Pharmacol 2005; 144:416-21. [PMID: 15655503 PMCID: PMC1576019 DOI: 10.1038/sj.bjp.0706094] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Somatostatin is a potent inhibitor of gastric acid secretion. Its effects are mediated through five specific receptor subtypes (sst(1-5)), of which sst(2) is dominant on the enterochromaffin-like (ECL) cell and the parietal cell. To study the paracrine mechanisms of somatostatin, the sst(2)-specific antagonist PRL-2903 was used. Effects of PRL-2903 on acid secretion and release of histamine were studied in the totally isolated, vascularly perfused rat stomach. Further, the release of histamine and gastrin after bombesin, alone and in combination with PRL-2903, were studied. Results are presented as mean+/-standard error of the mean (s.e.m.). PRL-2903 concentration-dependently increased the venous histamine concentration from basal 55.6+/-7.5 to 367+/-114 nM at 50 microM PRL-2903. With 10 microM PRL-2903, venous histamine output increased from baseline 6.2+/-0.5 to 20.9+/-4.9 nmol h(-1); P=0.008. The combination of 520 pM gastrin and 10 microM PRL-2903 increased venous histamine output from 41.7+/-7.3 nmol h(-1) with gastrin alone to 95.2+/-9.8 nmol h(-1); P=0.016. Further, 10 microM PRL-2903 increased acid output from baseline 8.5+/-1.8 to 37.4+/-11 micromol h(-1); P=0.017. When combined with 10 microM ranitidine, PRL-2903 did not significantly stimulate acid secretion. Bombesin/PRL-2903 increased venous histamine concentration from 50.4+/-14.8 to 292+/-64.2 nM; P=0.008, and gastrin concentration from 38.6+/-13.1 to 95.8+/-20.3 pM; P=0.037. Endogenous somatostatin exerts a continuous restraint on histamine and gastrin release from the gastric mucosa and significantly reduces baseline acid secretion.
Collapse
Affiliation(s)
- Vidar Fykse
- Department of Cancer Research and Molecular Medicine, Norwegian University of Science and Technology, NO-7489 Trondheim, Norway
| | - David H Coy
- Peptide Research Laboratories, Department of Medicine, Tulane University Health Sciences Center, 1430 Tulane Avenue, New Orleans, LA 70112, U.S.A
| | - Helge Lyder Waldum
- Department of Cancer Research and Molecular Medicine, Norwegian University of Science and Technology, NO-7489 Trondheim, Norway
| | - Arne Kristian Sandvik
- Department of Cancer Research and Molecular Medicine, Norwegian University of Science and Technology, NO-7489 Trondheim, Norway
- Author for correspondence:
| |
Collapse
|
17
|
Schirra J, Göke B. The physiological role of GLP-1 in human: incretin, ileal brake or more? ACTA ACUST UNITED AC 2005; 128:109-15. [PMID: 15780430 DOI: 10.1016/j.regpep.2004.06.018] [Citation(s) in RCA: 99] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2004] [Accepted: 06/17/2004] [Indexed: 12/22/2022]
Abstract
The proglucagon-derived peptide glucagon-like peptide-1 (GLP-1) is an intestinal signal peptide postprandially released from the L cells of the lower gut. Exogenously administered the synthetic hormone exerts a glucose-dependent insulinotropic effect at the pancreatic beta-cells and lowers plasma glucagon by an inhibitory effect against the alpha-cells. It delays gastric emptying by relaxation of the gastric fundus, inhibition of antral contractility, and stimulation of both the tonic and phasic motility of the pyloric sphincter. Enhancement of insulin, suppression of glucagon, and inhibition of gastric emptying are the main determinants controlling glucose homeostasis with GLP-1. Human studies employing the specific GLP-1 receptor antagonist exendin(9-39) show that endogenously released GLP-1 likewise controls fasting plasma glucagon, stimulates insulin, and influences all the motoric mechanisms known to control gastric emptying. Therefore, GLP-1 is discussed as an incretin hormone and as an enterogastrone in man. Synthetic GLP-1 also suppresses gastric acid and pancreatic enzyme secretion. The inhibitory effects on upper gastrointestinal functions are at least partly mediated by vagal-cholinergic inhibition and may involve interactions with vagal afferent pathways and/or circumventricular regions within the CNS. GLP-1 is a candidate humoral mediator of the 'ileal brake' exerting inhibition of upper gastrointestinal function preventing malabsorption and postprandial metabolic disturbances. As human studies indicate a central action of GLP-1 in reduction of food intake, it is uncertain if this is a consequence of induction of satiety or of transduction of visceral aversive stress signals.
Collapse
Affiliation(s)
- Jörg Schirra
- Department of Internal Medicine II, Marchioninistr. 15, University of Munich, Munich D-81377, Germany.
| | | |
Collapse
|
18
|
Piqueras L, Martínez V. Role of somatostatin receptors on gastric acid secretion in wild-type and somatostatin receptor type 2 knockout mice. NAUNYN-SCHMIEDEBERG'S ARCHIVES OF PHARMACOLOGY 2004; 370:510-20. [PMID: 15599710 DOI: 10.1007/s00210-004-0992-8] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/22/2004] [Accepted: 09/23/2004] [Indexed: 10/26/2022]
Abstract
Somatostatin, probably acting through somatostatin type 2 receptors (SSTR2), is the main inhibitor of gastric acid secretion. We characterized gastric acid secretion in SSTR2 knockout mice, and used preferential somatostatin receptor agonists to assess the relative role of SSTR1, 2, 3, 4, and 5 on gastric acid secretion. Basal gastric acid secretion and the secretory response to a meal were similar in conscious wild-type and knockout mice. However, under urethane anesthesia, which releases endogenous somatostatin, SSTR2 knockout mice had a basal secretion 11-15-fold higher than wild-type animals (micromol/10 min:1.40+/-0.09 vs. 0.10+/-0.01, p<0.05). Gastrin immunoneutralization or H(2) receptors blockade (cimetidine), but not cholinergic blockade (atropine), reduced the high basal secretion in SSTR2 knockout mice. In SSTR2 knockout mice, gastrin and histamine stimulated acid secretion with similar efficacy, while in wild-type mice histamine was more effective than gastrin. SSTR2 knockout mice showed also a hypersecretory response to pylorus ligation compared with wild-type animals. In wild-type mice, somatostatin-14, SMS 201-995, and the SSTR2-preferential agonist, DC 32-87, inhibited gastrin-stimulated acid secretion with an order of potency SMS 201-995>DC 32-87>somatostatin-14. Preferential agonists for the SSTR1, 3, 4, and 5 were devoid of any effect. None of the compounds tested affected the high basal secretion observed under urethane anesthesia in SSTR2 knockout mice. These results show that gastric antisecretory effects of peripheral somatostatin are mediated solely through SSTR2. In the absence of functional SSTR2 other somatostatin receptors do not compensate for the lack somatostatin-SSTR2-mediated inhibition. Basal acid secretion and the response to a meal are normal in conscious SSTR2 knockout mice, suggesting the presence of somatostatin-independent mechanisms that compensate for the lack of somatostatin-SSTR2-mediated inhibitory responses.
Collapse
Affiliation(s)
- Laura Piqueras
- Department of Physiology, Pharmacology and Toxicology, Cardenal Herrera CEU University, Valencia, Spain
| | | |
Collapse
|
19
|
Piqueras L, Taché Y, Martinez V. Galanin inhibits gastric acid secretion through a somatostatin-independent mechanism in mice. Peptides 2004; 25:1287-95. [PMID: 15350696 DOI: 10.1016/j.peptides.2004.06.003] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/19/2004] [Revised: 06/04/2004] [Accepted: 06/07/2004] [Indexed: 10/26/2022]
Abstract
The role of somatostatin in galanin-induced inhibition of gastric acid secretion in urethane-anesthetized mice was investigated by using immunoneutralization of endogenous somatostatin and somatostatin receptor type 2 (SSTR2) knockout mice. Intravenous galanin (10 and 20 microg/kg/h) inhibited pentagastrin-stimulated gastric acid secretion by 47 and 33%, respectively. Somatostatin antibody injected i.v. increased acid secretion by 3.5-fold over basal levels but did not modify the antisecretory effects of galanin. Urethane-anesthetized SSTR2 knockout mice had a basal secretion 14-fold higher than wild-type animals, that was inhibited by galanin (10 and 20 microg/kg/h) by 49 and 31% respectively. In mice galanin inhibits gastric acid secretion through a somatostatin-independent mechanism.
Collapse
Affiliation(s)
- Laura Piqueras
- Department of Physiology, Pharmacology and Toxicology, Cardenal Herrera CEU University, Valencia, Spain
| | | | | |
Collapse
|
20
|
Isbil-Buyukcoskun N, Gulec G. Effects of centrally injected GLP-1 in various experimental models of gastric mucosal damage. Peptides 2004; 25:1179-83. [PMID: 15245878 DOI: 10.1016/j.peptides.2004.05.001] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/11/2004] [Revised: 04/28/2004] [Accepted: 05/03/2004] [Indexed: 11/24/2022]
Abstract
Glucagon-like peptide-1 (GLP-1) is accepted to be a peptide involved in the central regulation of gastrointestinal function, but its potential gastroprotective effect is not clear. The aim of this study was to investigate whether intracerebroventricularly injected GLP-1 has protective effects on gastric mucosal lesions induced by several models, and if yes, whether these effects are due to the gastric antisecretory effect of the peptide. GLP-1 which was injected in three different doses (1, 10, 100 ng/10 microl; i.c.v.) to conscious rats prevented the mucosal lesions induced by reserpine and ethanol, but did not prevent the gastric mucosal lesions induced by pyloric ligation. In addition, 1 ng/10 microl dose of centrally injected GLP-1 inhibited gastric acid secretion in pylorus-ligated rats. As a result, we conclude that intracerebroventricularly injected GLP-1 may play a role in the prevention of gastric mucosal lesions induced by certain experimental models and this gastroprotective effect may be independent from its antisecretory effect.
Collapse
|
21
|
Piqueras L, Martinez V. Peripheral GABAB agonists stimulate gastric acid secretion in mice. Br J Pharmacol 2004; 142:1038-48. [PMID: 15210585 PMCID: PMC1575121 DOI: 10.1038/sj.bjp.0705876] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
1 We characterized the effects of intravenous GABA and preferential GABAA (muscimol), GABAB (R-baclofen and SKF-97541) and GABAC agonists (imidazole-4-acetic acid) on gastric acid secretion in urethane-anesthetized mice implanted with a gastric cannula, and determined the role of vagal cholinergic mechanisms, and gastrin and somatostatin by using peptide immunoneutralization, the SSTR2 antagonist, PRL-2903, and SSTR2 knockout mice. 2 The selective GABA(B) agonists R-baclofen (0.1-3 mg kg(-1), i.v.) and SKF-97541 (0.01-0.3 mg kg(-1), i.v.) induced a dose-related stimulation of gastric acid secretion. SKF-97541 was about 10 times more potent than R-baclofen stimulating gastric acid secretion. Neither GABA (0.1-100 mg kg(-1), i.v.) nor muscimol (0.1-3 mg kg(-1)) nor imidazole-4-acetic acid (0.1-10 mg kg(-1)) affected basal gastric acid secretion. 3 Stimulatory effects of SKF-97541 (0.1 mg kg(-1), i.v.) were blocked by the selective GABAB antagonist, 2-hydroxysaclofen, cholinergic blockade with atropine, subdiaphragmatic vagotomy or gastrin immunoneutralization. 4 Somatostatin immunoneutralization or SSTR2 blockade with PRL-2903 enhanced the secretory response to SKF-97541 (0.1 mg kg(-1), i.v.) by 78 and 105%, respectively. 5 In SSTR2 knockout mice, SKF-97541 (0.1 mg kg(-1), i.v.) increased basal gastric acid secretion by 48%. Neither GABA nor muscimol nor imidazole-4-acetic acid modified basal gastric acid secretion in SSTR2 knockout mice. 6 These results indicate that, in mice, stimulation of GABAB receptors increases gastric acid secretion through vagal- and gastrin-dependent mechanisms. Somatostatin implication might be secondary to the release of gastrin and the increase in gastric luminal acidity.
Collapse
MESH Headings
- Animals
- Antibodies, Monoclonal/pharmacology
- Atropine/pharmacology
- Baclofen/analogs & derivatives
- Baclofen/pharmacology
- Deoxyglucose/pharmacology
- Dose-Response Relationship, Drug
- GABA Agonists/pharmacology
- GABA Antagonists/pharmacology
- GABA-A Receptor Agonists
- GABA-B Receptor Agonists
- Gastric Acid/metabolism
- Gastrins/immunology
- Imidazoles/pharmacology
- Injections, Intravenous
- Male
- Mice
- Mice, Knockout
- Muscimol/pharmacology
- Organophosphorus Compounds/pharmacology
- Pentagastrin/pharmacology
- Peptides, Cyclic/pharmacology
- Receptors, GABA/drug effects
- Receptors, GABA/physiology
- Receptors, GABA-A/physiology
- Receptors, GABA-B/physiology
- Receptors, Somatostatin/antagonists & inhibitors
- Receptors, Somatostatin/genetics
- Receptors, Somatostatin/physiology
- Somatostatin/immunology
- Time Factors
- Vagotomy
- gamma-Aminobutyric Acid/pharmacology
Collapse
Affiliation(s)
- Laura Piqueras
- Department of Physiology, Pharmacology and Toxicology, Cardenal Herrera CEU University, Valencia, Spain
| | - Vicente Martinez
- Department of Physiology, Pharmacology and Toxicology, Cardenal Herrera CEU University, Valencia, Spain
- Author for correspondence:
| |
Collapse
|
22
|
Piqueras L, Taché Y, Martínez V. Peripheral PACAP inhibits gastric acid secretion through somatostatin release in mice. Br J Pharmacol 2004; 142:67-78. [PMID: 15023860 PMCID: PMC1574929 DOI: 10.1038/sj.bjp.0705739] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
1. Studies in rats suggest that PACAP modulates gastric acid secretion through the release of both histamine and somatostatin. 2. We characterized the effects of exogenous PACAP on gastric acid secretion in urethane-anesthetized mice implanted with a gastric cannula and in conscious 2-h pylorus ligated mice, and determined the involvement of somatostatin and somatostatin receptor type 2 (SSTR2) by using somatostatin immunoneutralization, the SSTR2 antagonist, PRL-2903, and SSTR2 knockout mice. 3. Urethane-anesthetized wild-type mice had low basal acid secretion (0.10+/-0.01 micromol (10 min)(-1)) compared with SSTR2 knockout mice (0.93+/-0.07 micromol (10 min)(-1)). Somatostatin antibody and PRL-2903 increased basal secretion in wild-type mice but not in SSTR2 knockout animals. 4. In wild-type urethane-anesthetized mice, PACAP-38 (3-270 microg kg(-1) h(-1)) did not affect the low basal acid secretion, but inhibited the acid response to pentagastrin, histamine, and bethanechol. 5. In wild-type urethane-anesthetized mice pretreated with somatostatin antibody or PRL-2903 and in SSTR2 knockout mice, peripheral infusion of PACAP-38 or somatostatin-14 did not inhibit the increased basal gastric acid secretion. 6. In conscious wild-type mice, but not in SSTR2 knockout mice, PACAP-38 inhibited gastric acid secretion induced by 2-h pylorus ligation. The antisecretory effect of PACAP-38 was prevented by immunoneutralization of somatostatin. 7. These results indicate that, in mice, peripheral PACAP inhibits gastric acid secretion through the release of somatostatin and the activation of SSTR2 receptors. There is no evidence for stimulatory effects of PACAP on acid secretion in mice.
Collapse
Affiliation(s)
- Laura Piqueras
- Department of Physiology, Pharmacology and Toxicology, Cardenal Herrera CEU University, Valencia, Spain
| | - Yvette Taché
- CURE:Digestive Diseases Research Center, Center for Neurovisceral Sciences, VA Greater Los Angeles Health Care System, Digestive Diseases Division, Department of Medicine and Brain Research Institute, University of California Los Angeles, Los Angeles, CA, U.S.A
| | - Vicente Martínez
- Department of Physiology, Pharmacology and Toxicology, Cardenal Herrera CEU University, Valencia, Spain
- Author for correspondence:
| |
Collapse
|
23
|
Abstract
The motor, modulatory, and sensory neurotransmitters that mediate the peristaltic reflex in the mouse colon were identified by direct measurement, and their involvement in various pathways was determined by selective receptor antagonists. Mucosal stimulation in the central compartment of a three-compartment flat sheet preparation of mouse colon elicited ascending contraction and descending relaxation in the orad and caudad compartments, respectively. Ascending contraction was accompanied by substance P release, a marker for excitatory neurotransmitter release, into the orad compartment and was partly inhibited by atropine and spantide, and abolished by a combination of the two antagonists. Descending relaxation was accompanied by vasoactive intestinal peptide (VIP) release, a marker for inhibitory neurotransmitter release, into the caudad compartment, and was partly inhibited by VIP10-28 and NG-nitro-L-arginine, and abolished by a combination of the two agents. Somatostatin release increased during descending relaxation: immunoneutralization of somatostatin or blockade of its effect with a selective somatostatin type 2 receptor antagonist inhibited descending relaxation. The delta-opioid receptor antagonist naltrindole augmented descending relaxation and ascending contraction. Calcitonin gene-related peptide (CGRP) release increased in the central compartment and was mediated by concurrent release of 5-hydroxytryptamine (5-HT) because its release was blocked by a 5-HT4 receptor antagonist. Both the latter and the CGRP antagonist CGRP8-37, inhibited ascending contraction and descending relaxation. Thus, the reflex in mouse like that in rat and human intestine is initiated by mucosal release of 5-HT and activation of 5-HT4 receptors on CGRP sensory neurons and is relayed via somatostatin and opioid interneurons to VIP/nitric-oxide synthase inhibitory motor neurons and via cholinergic interneurons to acetylcholine/tachykinin excitatory motor neurons.
Collapse
Affiliation(s)
- John R Grider
- Department of Physiology, P.O. Box 980551, Medical College of Virginia Campus, Virginia Commonwealth University, Richmond, VA 23298, USA.
| |
Collapse
|
24
|
Beales ILP, Calam J. Regulation of amylin release from cultured rabbit gastric fundic mucosal cells. BMC PHYSIOLOGY 2003; 3:13. [PMID: 14572315 PMCID: PMC269984 DOI: 10.1186/1472-6793-3-13] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/04/2003] [Accepted: 10/22/2003] [Indexed: 11/21/2022]
Abstract
Background Amylin (islet amyloid polypeptide) is a hormone with suggested roles in the regulation of glucose homeostasis, gastric motor and secretory function and gastroprotection. In the gastric mucosa amylin is found co-localised with somatostatin in D-cells. The factors regulating gastric amylin release are unknown. In this study we have investigated the regulation of amylin release from gastric mucosal cells in primary culture. Rabbit fundic mucosal cells enriched for D-cells by counterflow elutriation were cultured for 40 hours. Amylin and somatostatin release over 2 hours in response to agonists were assessed. Results Amylin release was significantly enhanced by activation of protein kinase C with phorbol-12-myristate-13-acetate, adenylate cyclase with forskolin and elevation of intracellular calcium with A23187. Cholecystokinin (CCK), epinephrine and glucagon-like peptide-1 (GLP-1) each stimulated amylin release in a dose-dependent manner. Maximal CCK-stimulated release was greater than either epinephrine or GLP-1, even when the effects of the latter two were enhanced by isobutylmethylxanthine. Stimulated amylin release was significantly inhibited by carbachol (by 51–59%) and octreotide (by 33–42%). Somatostatin release paralleled that of amylin. Conclusions The cultured D-cell model provides a means of studying amylin release. Amylin secretion is stimulated by receptor-dependent and -independent activation of Ca2+/protein kinase C and adenylate cyclase pathways. Inhibition involves activation of muscarinic receptors and auto-regulation by somatostatin.
Collapse
Affiliation(s)
- Ian LP Beales
- Gastrointestinal Research Unit, Department of Physiology and Cell Biology, School of Medicine, Health Policy and Practice, University of East Anglia, Norwich NR4 7TJ, United Kingdom
- Department of Gastroenterology, Norfolk and Norwich University Hospital NHS Trust, Norwich NR4 7UZ, United Kingdom
| | - John Calam
- Department of Medicine, Imperial College School of Medicine, Hammersmith Hospital, London W12 0NN, United Kingdom
| |
Collapse
|
25
|
Piqueras L, Taché Y, Martínez V. Somatostatin receptor type 2 mediates bombesin-induced inhibition of gastric acid secretion in mice. J Physiol 2003; 549:889-901. [PMID: 12692184 PMCID: PMC2342983 DOI: 10.1113/jphysiol.2003.039750] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Studies in isolated mouse stomach showed that bombesin releases somatostatin. We characterized the effects of exogenous bombesin on gastric acid secretion in mice and determined the involvement of somatostatin and somatostatin receptor type 2 (SSTR2) by using somatostatin immunoneutralization, the SSTR2 antagonist, PRL-2903, and SSTR2 knockout mice. Gastric acid secretion was monitored under basal and pentagastrin-, histamine- or bethanechol-stimulated conditions in urethane-anaesthetized mice. Bombesin (10-40 micro g kg-1 h-1) and somatostatin-14 (20 micro g kg-1 h-1) were infused I.V. 10 and 30 min after PRL-2903 or somatostatin antibody pretreatment, respectively. Urethane-anaesthetized wild-type mice had low basal acid secretion (0.12 +/- 0.01 micro mol (10 min)-1) compared with SSTR2 knockout mice (1.43 +/- 0.10 micro mol (10 min)-1). Somatostatin antibody and PRL-2903 increased basal secretion in wild-type mice but not in SSTR2 knockout animals. In wild-type mice, bombesin inhibited secretagogue-stimulated acid secretion in a dose-dependent manner, and somatostatin-14 inhibited pentagastrin-stimulated secretion. In wild-type mice pretreated with somatostatin antibody or PRL-2903 and in SSTR2 knockout mice, bombesin and somatostatin-14 I.V. infusion did not alter the increased gastric acid secretion. These results indicate that, in mice, bombesin inhibits gastric acid secretion through the release of somatostatin and the activation of SSTR2. These observations strengthen the important role of SSTR2 in mediating somatostatin inhibitory actions on gastric acid secretion.
Collapse
Affiliation(s)
- Laura Piqueras
- Department of Physiology, Pharmacology and Toxicology, Cardenal Herrera CEU University, Valencia, Spain
| | | | | |
Collapse
|
26
|
Cejvan K, Coy DH, Efendic S. Intra-islet somatostatin regulates glucagon release via type 2 somatostatin receptors in rats. Diabetes 2003; 52:1176-81. [PMID: 12716749 DOI: 10.2337/diabetes.52.5.1176] [Citation(s) in RCA: 91] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Exogenously administered somatostatin (SST) inhibits secretion of insulin and glucagon. Furthermore, it is hypothesized that islet SST regulates glucagon secretion by a local action. A number of studies utilizing SST antibodies have been performed to test this hypothesis, and their results have been conflicting. Five subtypes of SST receptor (SSTR1-5) mediate the effect of SST on target cells. In rodents, SST inhibits the release of glucagon, but not that of insulin, via SSTR2. A novel SSTR2-selective antagonist, DC-41-33, was synthesized recently. We have investigated the effects of this antagonist on arginine-stimulated glucagon and insulin release in batch incubations of isolated rat islets, perifused isolated rat islets, and isolated perfused rat pancreas. In batch incubations at 3.3 mmol/l glucose, DC-41-33 increased glucagon release in a dose-dependent manner. At the maximum dose tested (2 micro mol/l), DC-41-33 enhanced the glucagon response by 4.3- to 5-fold. Similarly, this compound increased arginine-induced glucagon release in perifused islets at 3.3 mmol/l glucose (2.8-fold) and perfused pancreas at 3.3 and 5.5 mmol/l glucose (2.5- and 2.3-fold, respectively). In the two latter experimental systems, DC-41-33 had no significant effect on insulin release. In conclusion, our results strongly support the hypothesis that islet SST inhibits glucagon secretion via a local action.
Collapse
Affiliation(s)
- Kenan Cejvan
- Department of Molecular Medicine, Endocrine and Diabetes Unit, Karolinska Hospital and Institute, L6:02, S-171 76 Stockholm, Sweden.
| | | | | |
Collapse
|
27
|
Nunn C, Langenegger D, Hurth K, Schmidt K, Fehlmann D, Hoyer D. Agonist properties of putative small-molecule somatostatin sst2 receptor-selective antagonists. Eur J Pharmacol 2003; 465:211-8. [PMID: 12681432 DOI: 10.1016/s0014-2999(03)01482-1] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
The availability of antagonist ligands for somatostatin receptors is very limited, with those that are available often displaying agonist properties or limited receptor subtype selectivity. Hay et al. [Bioorg. Med. Chem. Lett. 11 (2001) 2731] recently described the development of small-molecule somatostatin receptor subtype 2 (sst(2)) selective compounds. This study investigates the binding affinity and functional characteristics of two of those antagonists (2 and 3) and the agonist compound, from which they were derived (1). In radioligand binding studies using the agonist radioligands [125I][Tyr(11)]SRIF-14 (Ala-Gly-c[Cys-Lys-Asn-Phe-Phe-Trp-Lys-Thr-(125I-Tyr)-Thr-Ser-Cys]-OH), [125I]LTT-SRIF-28 ([Leu(8),DTrp(22),125I-Tyr(25)]SRIF-28; Ser-Ala-Asn-Ser-Asn-Pro-Ala-Leu-Ala-Pro-Arg-Glu-Arg-Lys-Ala-Gly-c[Cys-Lys-Asn-Phe-Phe-DTrp-Lys-Thr-(125I-Tyr)-Thr-Ser-Cys]-OH), [125I]CGP 23996 (c[Lys-Asu-Phe-Phe-Trp-Lys-Thr-(125I-Tyr)-Thr-Ser]), [125I][Tyr(3)]octreotide (DPhe-c[Cys-(125I-Tyr)-DTrp-Lys-Thr-Cys]-Thr-OH) and [125I][Tyr(10)]cortistatin-14 (Pro-c[Cys-Lys-Asn-Phe-Phe-Trp-Lys-Thr-(125I-Tyr)-Ser-Ser-Cys]-Lys) at human recombinant somatostatin receptors expressed in Chinese hamster lung fibroblast (CCL39) cells and native rat cortex, the compounds bound with high affinity (pK(d) 6.8-9.7) and selectivity to human sst(2) receptors. Some affinity was also observed for sst(5) labelled by [125I][Tyr(3)]octreotide and [125I]CGP 23996. In functional studies at human sst(2) receptors expressed in Chinese hamster ovary (CHO) cells, both the agonist 1 and the two putative antagonists 2 and 3 concentration dependently inhibited forskolin-stimulated adenylate cyclase and stimulated luciferase reporter gene expression, with similar efficacy to the natural ligand somatotropin release inhibiting factor (SRIF)-14. Compound 1 had similar potency to SRIF-14, which was in the nanomolar range, whereas 2 and 3 were 10-100-fold less potent. The intrinsic activity of 2 and 3 was too high to allow antagonist studies to be carried out. In conclusion, in contrast to previous findings, all three compounds are potent agonists at recombinant human sst(2) receptors.
Collapse
Affiliation(s)
- Caroline Nunn
- Nervous System Research, Novartis Pharma AG, CH-4002, Basel, Switzerland
| | | | | | | | | | | |
Collapse
|
28
|
Hirsch AB, McCuen RW, Arimura A, Schubert ML. Adrenomedullin stimulates somatostatin and thus inhibits histamine and acid secretion in the fundus of the stomach. REGULATORY PEPTIDES 2003; 110:189-95. [PMID: 12573799 DOI: 10.1016/s0167-0115(02)00208-2] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Adrenomedullin has recently been localized to enterochromaffin-like (ECL) and chief cells in the gastric fundus. It has been proposed that adrenomedullin may play a role in gastric mucosal defense and repair. In the present study, we have used the isolated, luminally perfused mouse stomach and superfused rat fundic segments to examine the effect of adrenomedullin on exocrine and endocrine secretion in this region of the stomach. Addition of adrenomedullin (1 pM to 1 microM) to the isolated mouse stomach caused a concentration-dependent decrease in acid secretion. The EC(50) value was 1.4 x 10(-9) and maximal inhibition of acid secretion was obtained at a concentration of 1 microM (31+/-4% below basal level, P<0.001). In rat fundic segments, superfusion with adrenomedullin (0.1 pM to 0.1 microM) caused a concentration-dependent increase in somatostatin secretion (EC(50), 1 x 10(-10)) that was accompanied by a reciprocal decrease in histamine secretion (EC(50), 1.2 x 10(-11)). Maximal stimulation of somatostatin secretion (60+/-5% above basal level, P<0.001) and inhibition of histamine secretion (50+/-5% below basal level, P<0.01) was obtained at a concentration of 0.1 microM. Changes in acid and histamine secretion induced by adrenomedullin reflected changes in somatostatin secretion and could be abolished by addition of somatostatin antibody. The axonal blocker, tetrodotoxin, also abolished the somatostatin and, consequently, the acid and histamine responses to adrenomedullin, implying that the effect of adrenomedullin on somatostatin secretion was mediated via activation of intramural neurons. We conclude that adrenomedullin, acting via intramural fundic neurons, stimulates somatostatin and thus inhibits histamine and acid secretion. This represents one mechanism by which adrenomedullin might enhance mucosal defense and repair.
Collapse
Affiliation(s)
- Ari B Hirsch
- Department of Medicine, Medical College of Virginia/Virginia Commonwealth University, Richmond, VA, USA
| | | | | | | |
Collapse
|
29
|
Cheng H, Yibchok-anun S, Coy DH, Hsu WH. SSTR2 mediates the somatostatin-induced increase in intracellular Ca(2+) concentration and insulin secretion in the presence of arginine vasopressin in clonal beta-cell HIT-T15. Life Sci 2002; 71:927-36. [PMID: 12084389 DOI: 10.1016/s0024-3205(02)01774-5] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The effects of somatostatin (SRIF) are mediated through the seven transmembrane receptor family that signals via Gi/Go. To date, five distinct SRIF receptors have been characterized and designated SSTR1-5. We have characterized the SRIF receptor that mediates the increase in [Ca(2+)](i) and insulin secretion in HIT-T15 cells (Simian virus 40-transformed Syrian hamster islets) using high affinity, subtype selective agonists for SSTR1 (L-797,591), SSTR2 (L-779,976), SSTR3 (L-796,778), SSTR4 (L-803,087), SSTR5 (L-817,818) and PRL-2903, a specific SSTR2 antagonist. In the presence of arginine vasopressin (AVP), SRIF increased [Ca(2+)](i) and insulin secretion. Treatment with the SSTR2 agonist L-779,976 resulted in similar responses to SRIF. In addition, L-779,976 increased both [Ca(2+)](i) and insulin secretion in a dose-dependent manner. Treatment with L-779,976 alone did not alter [Ca(2+)](i) or basal insulin secretion. In the presence of AVP, all other SRIF receptor agonists failed to increase [Ca(2+)](i) and insulin secretion. The effects of SRIF and L-779,976 were abolished by the SSTR2 antagonist PRL-2903. Our results suggest that the mechanism underlying SRIF-induced insulin secretion in HIT-T15 cells be mediated through the SSTR2.
Collapse
Affiliation(s)
- Henrique Cheng
- Department of Biomedical Sciences, College of Veterinary Medicine, Iowa State University, Ames, IA 50011 USA
| | | | | | | |
Collapse
|
30
|
Zaki M, Koduru S, McCuen R, Vuyyuru L, Schubert ML. Amylin, released from the gastric fundus, stimulates somatostatin and thus inhibits histamine and acid secretion in mice. Gastroenterology 2002; 123:247-55. [PMID: 12105853 DOI: 10.1053/gast.2002.34176] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
BACKGROUND & AIMS Amylin, a peptide that displays 50% homology with calcitonin gene-related peptide (CGRP), is colocalized with somatostatin in endocrine cells of the gastric fundus. The present study was designed to determine the mechanism of action of amylin on gastric exocrine and endocrine secretion. METHODS Acid secretion was measured in the isolated mouse stomach by titration. Somatostatin and histamine secretion were measured in rat fundic segments by radioimmunoassay. RESULTS In isolated mouse stomach, amylin caused a concentration-dependent decrease in acid secretion. In rat fundic segments, amylin and CGRP each caused a concentration-dependent increase in somatostatin and a decrease in histamine secretion. Changes in histamine secretion induced by amylin reflected changes in somatostatin secretion and could be abolished by addition of somatostatin antibody. Both the somatostatin and the histamine responses to amylin were abolished by the selective amylin antagonist AC187 but were unaffected by the CGRP antagonist CGRP8-37. In contrast, the responses to CGRP were abolished by CGRP8-37 but were unaffected by AC187. AC187 alone decreased somatostatin and increased histamine in fundic segments and increased acid secretion in isolated stomach, indicating that endogenous amylin participates in the regulation of gastric endocrine (somatostatin and histamine) and exocrine (acid) secretion. CONCLUSIONS In gastric fundus, release of amylin from somatostatin cells interacts with distinct amylin receptors to enhance somatostatin secretion via an autocrine pathway that leads to inhibition of histamine and acid secretion.
Collapse
Affiliation(s)
- Muhammad Zaki
- Department of Medicine, Medical College of Virginia, Virginia Commonwealth University, Richmond, Virginia, USA
| | | | | | | | | |
Collapse
|
31
|
Abstract
The glucagon-like peptides (GLP-1 and GLP-2) are proglucagon-derived peptides cosecreted from gut endocrine cells in response to nutrient ingestion. GLP-1 acts as an incretin to lower blood glucose via stimulation of insulin secretion from islet beta cells. GLP-1 also exerts actions independent of insulin secretion, including inhibition of gastric emptying and acid secretion, reduction in food ingestion and glucagon secretion, and stimulation of beta-cell proliferation. Administration of GLP-1 lowers blood glucose and reduces food intake in human subjects with type 2 diabetes. GLP-2 promotes nutrient absorption via expansion of the mucosal epithelium by stimulation of crypt cell proliferation and inhibition of apoptosis in the small intestine. GLP-2 also reduces epithelial permeability, and decreases meal-stimulated gastric acid secretion and gastrointestinal motility. Administration of GLP-2 in the setting of experimental intestinal injury is associated with reduced epithelial damage, decreased bacterial infection, and decreased mortality or gut injury in rodents with chemically induced enteritis, vascular-ischemia reperfusion injury, and dextran sulfate-induced colitis. GLP-2 also attenuates chemotherapy-induced mucositis via inhibition of drug-induced apoptosis in the small and large bowel. GLP-2 improves intestinal adaptation and nutrient absorption in rats after major small bowel resection, and in humans with short bowel syndrome. The actions of GLP-2 are mediated by a distinct GLP-2 receptor expressed on subsets of enteric nerves and enteroendocrine cells in the stomach and small and large intestine. The beneficial actions of GLP-1 and GLP-2 in preclinical and clinical studies of diabetes and intestinal disease, respectively, has fostered interest in the potential therapeutic use of these gut peptides. Nevertheless, the actions of the glucagon-like peptides are limited in duration by enzymatic inactivation via cleavage at the N-terminal penultimate alanine by dipeptidyl peptidase IV (DP IV). Hence, inhibitors of DP IV activity, or DP IV-resistant glucagon-like peptide analogues, may be alternative therapeutic approaches for treatment of human diseases.
Collapse
Affiliation(s)
- Daniel J Drucker
- The Banting and Best Diabetes Centre, Department of Medicine, Toronto General Hospital, University of Toronto, Toronto, Ontario, Canada.
| |
Collapse
|
32
|
Guidobono F, Pagani F, Sibilia V, Soglian A, Rapetti D, Netti C. The role of sensory neurons in the antiulcer effect of centrally injected amylin in rat. Peptides 2000; 21:1537-41. [PMID: 11068101 DOI: 10.1016/s0196-9781(00)00308-9] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Central administration of amylin (2.2 microg/rat, i.c.v.) reduces (from a minimum of 67% to 83%) indomethacin (Indo, 20 mg Kg(-1), orally) induced ulcers in rats. The anti-ulcer effect of the peptide is not removed by the administration of prokinetic drugs like domperidone or neostigmine but it is reduced by 35% in rats treated with capsaicin or with the CGRP antagonist, CGRP(8-37). These data indicate that amylin gastroprotection involves capsaicin-sensitive nerve fiber leading to CGRP-dependent gastric vasodilatory effect. Additional mechanisms could involve noradrenergic alpha(2) receptors as the peptide gastroprotective activity is reduced from 67% to 20% by the alpha(2) antagonist yohimbine.
Collapse
Affiliation(s)
- F Guidobono
- Department of Pharmacology, Chemotherapy and Medical Toxicology, University of Milan, Via Vanvitelli 32, 20129, Milano, Italy.
| | | | | | | | | | | |
Collapse
|
33
|
Kreienkamp HJ, Akgün E, Baumeister H, Meyerhof W, Richter D. Somatostatin receptor subtype 1 modulates basal inhibition of growth hormone release in somatotrophs. FEBS Lett 1999; 462:464-6. [PMID: 10622746 DOI: 10.1016/s0014-5793(99)01582-3] [Citation(s) in RCA: 72] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Somatostatin (SST) inhibits the secretion of many peptide hormones including growth hormone (GH). The various functions of SST are mediated through at least five different receptor subtypes (SSTR1-5), their precise physiological roles have not been solved yet. Here we report on studies concerning the functional role of SSTR1 in the modulation of GH release from somatotrophs. Primary cell cultures from pituitaries of wild-type SSTR1 mice exposed to the SSTR1 selective somatostatin analog CH-275 show reduction of basal levels of GH secretion whereas somatotrophs isolated from SSTR1 null mutant mice did not respond to the agonist-mediated effect. This suggests that SSTR1 is involved in modulating basal GH levels in primary pituitary cell cultures and, together with SSTR2, may control the secretion of GH in the body.
Collapse
Affiliation(s)
- H J Kreienkamp
- Institut für Zellbiochemie und klinische Neurobiologie, Universität Hamburg, Germany
| | | | | | | | | |
Collapse
|
34
|
Abstract
This paper summarizes important developments, published over the past year, that improve our understanding of the regulation of gastric acid secretion at the central, peripheral, and intracellular levels and mechanisms by which various neurotransmitters, paracrine agents, and hormones regulate gastric secretion and are themselves regulated. The main stimulants of acid secretion from the parietal cell are histamine, gastrin, and acetylcholine. Histamine, released from fundic enterochromaffin-like cells, interacts with H(2) receptors on parietal cells that are coupled via separate G proteins to activation of adenylate cyclase and phospholipase C. The antral hormone gastrin, released by activation of cholinergic and bombesin/gastrin-releasing peptide neurons, acts mainly by release of histamine from enterochromaffin-like cells. Acetylcholine, released from gastric intramural neurons, interacts with muscarinic M(3) receptors on parietal cells and has little, if any, effect on histamine secretion. The main inhibitor of acid secretion is somatostatin, which, acting via sst(2) receptors, exerts a tonic restraint on parietal, enterochromaffin-like, and gastrin cells. In patients with duodenal ulcer, infection with Helicobacter pylori is associated with increased basal and stimulated plasma gastrin concentrations and acid outputs. The precise mechanisms mediating the effects are not known, but evidence suggests that both products of the bacteria and the inflammatory infiltrate are capable of stimulating gastrin and acid secretion.
Collapse
Affiliation(s)
- M L Schubert
- Department of Medicine, Division of Gastroenterology, Medical College of Virginia and McGuire VAMC, Richmond, Virginia 23249, USA.
| |
Collapse
|
35
|
Kawakubo K, Coy DH, Walsh JH, Taché Y. Urethane-induced somatostatin mediated inhibition of gastric acid: reversal by the somatostatin 2 receptor antagonist, PRL-2903. Life Sci 1999; 65:PL115-20. [PMID: 10499878 DOI: 10.1016/s0024-3205(99)00340-9] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Urethane increases the release of somatostatin (SRIF) which inhibits gastric acid secretion. The SRIF monoclonal antibody, CURE.S6 and the novel sst2 antagonist, PRL-2903 injected intravenously at maximal effective doses increased gastric acid secretion by 2 and 10 fold respectively from basal values within 30 min in urethane-anesthetized rats. Plasma gastrin levels were elevated 2.5 fold within 15 min by PRL-2903 (1.3 micromol/kg, i.v.). These data indicate that the low gastrin and acid secretion levels induced by urethane result from endogenous SRIF acting on sst2 and that PRL-2903 is a valuable SRIF antagonist to assess sst2 mediated events.
Collapse
Affiliation(s)
- K Kawakubo
- CURE: Digestive Diseases Research Center, VA Medical Center West Los Angeles, and Department of Medicine, UCLA, CA 90073, USA
| | | | | | | |
Collapse
|
36
|
Tingstedt JE, Edlund H, Madsen OD, Larsson LI. Gastric amylin expression. Cellular identity and lack of requirement for the homeobox protein PDX-1. A study in normal and PDX-1-deficient animals with a cautionary note on antiserum evaluation. J Histochem Cytochem 1999; 47:973-80. [PMID: 10424881 DOI: 10.1177/002215549904700801] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
The gene encoding amylin is implicated in the generation of amyloid in the islets of Langerhans of diabetics and is believed to be regulated by the homeodomain transcription factor PDX-1. Although gastric mucosa also produces amylin, studies on its cellular site of production have yielded highly divergent results, localizing this peptide to either gastrin, serotonin, or somatostatin cells or to combinations thereof. Using region-specific amylin antisera in combination with reverse transcriptase-polymerase chain reaction, we now document that the majority of cells expressing amylin correspond to somatostatin cells. Only a small subpopulation of gastrin cells contained immunoreactive amylin. Studies of PDX-1-deficient mice, which fail to develop gastrin cells while possessing normal numbers of somatostatin cells, revealed no detectable change in gastric amylin expression. These data show that neither normal gastrin cell development nor PDX-1 expression is needed for gastric amylin expression.
Collapse
Affiliation(s)
- J E Tingstedt
- Division of Cell Biology, Department of Anatomy, The Royal Veterinary and Agricultural University, Frederiksberg, Denmark
| | | | | | | |
Collapse
|
37
|
Hocart SJ, Jain R, Murphy WA, Taylor JE, Coy DH. Highly potent cyclic disulfide antagonists of somatostatin. J Med Chem 1999; 42:1863-71. [PMID: 10354394 DOI: 10.1021/jm9806289] [Citation(s) in RCA: 69] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The search for synthetic analogues of somatostatin (SRIF) which exhibit selective affinities for the five known receptor subtypes (sst1-5) has generated a large number of potent agonist analogues. Many of these agonists display good subtype selectivities and affinities for the subtypes 2, 3, and 5, with very few selective for sst1 or sst4. Until the recent report by Bass and co-workers (Mol. Pharmacol. 1996, 50, 709-715; erratum Mol. Pharmacol. 1997, 51, 170), no true antagonists of somatostatin had been discovered, let alone any displaying differential receptor subtype selectivity. In this present study, we further explore the effect of this putative L,5D6 antagonist motif on somatostatin octapeptide analogues with a cyclic hexapeptide core. The most potent antagonist found to date is H-Cpa-cyclo[DCys-Tyr-DTrp-Lys-Thr-Cys]-Nal-NH2, PRL-2970 (21), which has an IC50 of 1.1 nM in a rat pituitary growth hormone in vitro antagonist assay versus SRIF (1 nM). This analogue bound to cloned human somatostatin subtype 2 receptors with a Ki of 26 nM. The highest hsst2 affinity analogue was H-Cpa-cyclo[DCys-Pal-DTrp-Lys-Tle-Cys]-Nal-NH2, PRL-2915 (15), with a Ki of 12 nM (IC50 = 1.8 nM). This analogue was also selective for hsst2 over hsst3 and hsst5 by factors of 8 and 40, respectively, and had no agonist activity when tested alone at concentrations up to 10 microM. Regression analysis of the binding affinities versus the observed antagonist potencies revealed high correlations for hsst2 (r = 0.65) and hsst3 (r = 0.52) with a less significant correlation to hsst5 (r = 0.40). This is quite different from the somatostatin agonist analogues which show a highly significant correlation to hsst2 (r > 0.9). Receptor-selective somatostatin antagonists should provide valuable tools for characterizing the many important physiological functions of this neuropeptide.
Collapse
MESH Headings
- Animals
- CHO Cells
- Cell Membrane/metabolism
- Cricetinae
- Humans
- In Vitro Techniques
- Male
- Oligopeptides/chemical synthesis
- Oligopeptides/chemistry
- Oligopeptides/metabolism
- Oligopeptides/pharmacology
- Peptides, Cyclic/chemical synthesis
- Peptides, Cyclic/chemistry
- Peptides, Cyclic/metabolism
- Peptides, Cyclic/pharmacology
- Pituitary Gland, Anterior/cytology
- Pituitary Gland, Anterior/metabolism
- Radioligand Assay
- Rats
- Receptors, Somatostatin/agonists
- Receptors, Somatostatin/antagonists & inhibitors
- Receptors, Somatostatin/biosynthesis
- Receptors, Somatostatin/metabolism
- Structure-Activity Relationship
- Transfection
Collapse
Affiliation(s)
- S J Hocart
- Peptide Research Laboratories, Tulane University School of Medicine, New Orleans, Louisiana 70112, USA
| | | | | | | | | |
Collapse
|
38
|
Chapter 21. Non-peptide Somatostatin Receptor Ligands. ANNUAL REPORTS IN MEDICINAL CHEMISTRY 1999. [DOI: 10.1016/s0065-7743(08)60583-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register]
|