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Yuen KCJ, Hjortebjerg R, Ganeshalingam AA, Clemmons DR, Frystyk J. Growth hormone/insulin-like growth factor I axis in health and disease states: an update on the role of intra-portal insulin. Front Endocrinol (Lausanne) 2024; 15:1456195. [PMID: 39665021 PMCID: PMC11632222 DOI: 10.3389/fendo.2024.1456195] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/28/2024] [Accepted: 10/22/2024] [Indexed: 12/13/2024] Open
Abstract
Growth hormone (GH) is the key regulator of insulin-like growth factor I (IGF-I) generation in healthy states. However, portal insulin delivery is also an essential co-player in the regulation of the GH/IGF-I axis by affecting and regulating hepatic GH receptor synthesis, and subsequently altering hepatic GH sensitivity and IGF-I generation. Disease states of GH excess (e.g., acromegaly) and GH deficiency (e.g., congenital isolated GH deficiency) are characterized by increased and decreased GH, IGF-I and insulin levels, respectively, where the GH/IGF-I relationship is reflected by a "primary association". When intra-portal insulin levels are increased (e.g., obesity, Cushing's syndrome, or due to treatment with glucocorticoids and glucagon-like peptide 1 receptor agonists) or decreased (e.g., malnutrition, anorexia nervosa and type 1 diabetes mellitus), these changes secondarily alter hepatic GH sensitivity resulting in a "secondary association" with discordant GH and IGF-I levels (e.g., high GH/low IGF-I levels or low GH/high IGF-I levels, respectively). Additionally, intra-portal insulin regulates hepatic secretion of IGFBP-1, an inhibitor of IGF-I action. Through its effects on IGFBP-1 and subsequently free IGF-I, intra-portal insulin exerts its effects to influence endogenous GH secretion via the negative feedback loop. Therefore, it is important to understand the effects of changes in intra-portal insulin when interpreting the GH/IGF-I axis in disease states. This review summarizes our current understanding of how changes in intra-portal insulin delivery to the liver in health, disease states and drug therapy use and misuse that leads to alterations in GH/IGF-I secretion that may dictate management decisions in afflicted patients.
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Affiliation(s)
- Kevin C. J. Yuen
- Department of Neuroendocrinology and Neurosurgery, Barrow Neurological Institute, University of Arizona College of Medicine and Creighton School of Medicine, Phoenix, AZ, United States
| | - Rikke Hjortebjerg
- Department of Endocrinology, Odense University Hospital, Odense, Denmark
- Department of Clinical Medicine, Faculty of Health Sciences, University of Southern Denmark, Odense, Denmark
- Steno Diabetes Center Odense, Odense University Hospital, Odense, Denmark
| | - Ashok Ainkaran Ganeshalingam
- Department of Endocrinology, Odense University Hospital, Odense, Denmark
- Department of Clinical Medicine, Faculty of Health Sciences, University of Southern Denmark, Odense, Denmark
- Steno Diabetes Center Odense, Odense University Hospital, Odense, Denmark
| | - David R. Clemmons
- Department of Medicine, University of North Carolina School of Medicine, Chapel Hill, NC, United States
| | - Jan Frystyk
- Department of Endocrinology, Odense University Hospital, Odense, Denmark
- Department of Clinical Medicine, Faculty of Health Sciences, University of Southern Denmark, Odense, Denmark
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Wójcik M, Zieba DA, Bochenek J, Krawczyńska A, Barszcz M, Gajewska A, Antushevich H, Herman AP. The Effect of Endotoxin-Induced Inflammation on the Activity of the Somatotropic Axis in Sheep. Int J Inflam 2024; 2024:1057299. [PMID: 39149693 PMCID: PMC11325012 DOI: 10.1155/2024/1057299] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2024] [Revised: 05/31/2024] [Accepted: 07/27/2024] [Indexed: 08/17/2024] Open
Abstract
The hypothalamic-pituitary-somatotropic (HPS) axis controls many physiological and pathophysiological processes. The phenomenon of insensitivity to growth hormone resistance (GHres) was previously reported to be due to the development of inflammation. Therefore, the primary aim of the study was to determine the impact of inflammation caused by lipopolysaccharides (LPS) on the secretory activity of the HPS axis in sheep. The further goal was to determine the effect of inflammatory factors on individual components involved in intracellular signal transduction to GH via the GH receptor (GHR). The research was carried out on 24 seasonal sheep kept under a short-day photoperiod, randomly divided into two groups. Before the experiment, the sheep estrous cycles were synchronized. The results of the current study in a sheep model showed that inflammation impairs the activity of the somatotropic axis. On the one hand, LPS injection stimulated (p < 0.01) GH secretion, and on the other hand, it reduced the liver's sensitivity to this hormone by directly reducing (p < 0.01) GHR expression and activating the GHR inhibitory signal transduction mechanism. A symptom of such an inhibitory postreceptor signaling pathway may be due to an increase in SOCS3 expression (p < 0.01). The effect of various inhibition pathways is a significant reduction in the expression of the main transcription activator IGF1-STAT5B (p < 0.05). The action of GHres in the liver resulted in the inhibition of IGF1 secretion, which in the long term may have negative consequences for growth and development. Our study suggests that disruption of the GH cell signaling pathway may be one of the important elements of the pathophysiology of inflammation. It can suppress growth and hepatic metabolism to spare energy expenditure.
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Affiliation(s)
- Maciej Wójcik
- The Kielanowski Institute of Animal Physiology and Nutrition Polish Academy of Sciences, Instytucka 3 Street, Jabłonna 05-110, Poland
| | - Dorota Anna Zieba
- Department of Nutrition and Animal Biotechnology, and Fisheries Faculty of Animal Sciences University of Agriculture in Krakow, Krakow 31-120, Poland
| | - Joanna Bochenek
- The Kielanowski Institute of Animal Physiology and Nutrition Polish Academy of Sciences, Instytucka 3 Street, Jabłonna 05-110, Poland
| | - Agata Krawczyńska
- The Kielanowski Institute of Animal Physiology and Nutrition Polish Academy of Sciences, Instytucka 3 Street, Jabłonna 05-110, Poland
| | - Marcin Barszcz
- The Kielanowski Institute of Animal Physiology and Nutrition Polish Academy of Sciences, Instytucka 3 Street, Jabłonna 05-110, Poland
| | - Alina Gajewska
- The Kielanowski Institute of Animal Physiology and Nutrition Polish Academy of Sciences, Instytucka 3 Street, Jabłonna 05-110, Poland
| | - Hanna Antushevich
- The Kielanowski Institute of Animal Physiology and Nutrition Polish Academy of Sciences, Instytucka 3 Street, Jabłonna 05-110, Poland
| | - Andrzej Przemysław Herman
- The Kielanowski Institute of Animal Physiology and Nutrition Polish Academy of Sciences, Instytucka 3 Street, Jabłonna 05-110, Poland
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Reis MDDS, Veneziani LP, Porto FL, Lins MP, Mendes-da-Cruz DA, Savino W. Intrathymic somatotropic circuitry: consequences upon thymus involution. Front Immunol 2023; 14:1108630. [PMID: 37426675 PMCID: PMC10323194 DOI: 10.3389/fimmu.2023.1108630] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2022] [Accepted: 06/05/2023] [Indexed: 07/11/2023] Open
Abstract
Growth hormone (GH) is a classic pituitary-derived hormone crucial to body growth and metabolism. In the pituitary gland, GH production is stimulated by GH-releasing hormone and inhibited by somatostatin. GH secretion can also be induced by other peptides, such as ghrelin, which interacts with receptors present in somatotropic cells. It is well established that GH acts directly on target cells or indirectly by stimulating the production of insulin-like growth factors (IGFs), particularly IGF-1. Notably, such somatotropic circuitry is also involved in the development and function of immune cells and organs, including the thymus. Interestingly, GH, IGF-1, ghrelin, and somatostatin are expressed in the thymus in the lymphoid and microenvironmental compartments, where they stimulate the secretion of soluble factors and extracellular matrix molecules involved in the general process of intrathymic T-cell development. Clinical trials in which GH was used to treat immunocompromised patients successfully recovered thymic function. Additionally, there is evidence that the reduction in the function of the somatotropic axis is associated with age-related thymus atrophy. Treatment with GH, IGF-1 or ghrelin can restore thymopoiesis of old animals, thus in keeping with a clinical study showing that treatment with GH, associated with metformin and dehydroepiandrosterone, could induce thymus regeneration in healthy aged individuals. In conclusion, the molecules of the somatotrophic axis can be envisioned as potential therapeutic targets for thymus regeneration in age-related or pathological thymus involution.
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Affiliation(s)
- Maria Danielma dos Santos Reis
- Laboratory of Cell Biology, Institute of Biological and Health Sciences, Federal University of Alagoas, Maceió, Brazil
- Oswaldo Cruz Institute, Oswaldo Cruz Foundation, Brazilian National Institute of Science and Technology on Neuroimmunomodulation (INCT-NIM), Rio de Janeiro, Brazil
| | - Luciana Peixoto Veneziani
- Oswaldo Cruz Institute, Oswaldo Cruz Foundation, Brazilian National Institute of Science and Technology on Neuroimmunomodulation (INCT-NIM), Rio de Janeiro, Brazil
- Laboratory on Thymus Research, Oswaldo Cruz Institute, Oswaldo Cruz Foundation, Rio de Janeiro, Brazil
- Rio de Janeiro Research Network on Neuroinflammation, Oswaldo Cruz Institute, Oswaldo Cruz Foundation, Rio de Janeiro, Brazil
- INOVA-IOC Network on Neuroimmunomodulation, Oswaldo Cruz Institute (IOC), Oswaldo Cruz Foundation, Rio de Janeiro, Brazil
| | - Felipe Lima Porto
- Laboratory of Cell Biology, Institute of Biological and Health Sciences, Federal University of Alagoas, Maceió, Brazil
- Oswaldo Cruz Institute, Oswaldo Cruz Foundation, Brazilian National Institute of Science and Technology on Neuroimmunomodulation (INCT-NIM), Rio de Janeiro, Brazil
| | - Marvin Paulo Lins
- Laboratory of Cell Biology, Institute of Biological and Health Sciences, Federal University of Alagoas, Maceió, Brazil
- Oswaldo Cruz Institute, Oswaldo Cruz Foundation, Brazilian National Institute of Science and Technology on Neuroimmunomodulation (INCT-NIM), Rio de Janeiro, Brazil
| | - Daniella Arêas Mendes-da-Cruz
- Oswaldo Cruz Institute, Oswaldo Cruz Foundation, Brazilian National Institute of Science and Technology on Neuroimmunomodulation (INCT-NIM), Rio de Janeiro, Brazil
- Laboratory on Thymus Research, Oswaldo Cruz Institute, Oswaldo Cruz Foundation, Rio de Janeiro, Brazil
- Rio de Janeiro Research Network on Neuroinflammation, Oswaldo Cruz Institute, Oswaldo Cruz Foundation, Rio de Janeiro, Brazil
- INOVA-IOC Network on Neuroimmunomodulation, Oswaldo Cruz Institute (IOC), Oswaldo Cruz Foundation, Rio de Janeiro, Brazil
| | - Wilson Savino
- Oswaldo Cruz Institute, Oswaldo Cruz Foundation, Brazilian National Institute of Science and Technology on Neuroimmunomodulation (INCT-NIM), Rio de Janeiro, Brazil
- Laboratory on Thymus Research, Oswaldo Cruz Institute, Oswaldo Cruz Foundation, Rio de Janeiro, Brazil
- Rio de Janeiro Research Network on Neuroinflammation, Oswaldo Cruz Institute, Oswaldo Cruz Foundation, Rio de Janeiro, Brazil
- INOVA-IOC Network on Neuroimmunomodulation, Oswaldo Cruz Institute (IOC), Oswaldo Cruz Foundation, Rio de Janeiro, Brazil
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GPR101 drives growth hormone hypersecretion and gigantism in mice via constitutive activation of G s and G q/11. Nat Commun 2020; 11:4752. [PMID: 32958754 PMCID: PMC7506554 DOI: 10.1038/s41467-020-18500-x] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2019] [Accepted: 08/25/2020] [Indexed: 12/16/2022] Open
Abstract
Growth hormone (GH) is a key modulator of growth and GH over-secretion can lead to gigantism. One form is X-linked acrogigantism (X-LAG), in which infants develop GH-secreting pituitary tumors over-expressing the orphan G-protein coupled receptor, GPR101. The role of GPR101 in GH secretion remains obscure. We studied GPR101 signaling pathways and their effects in HEK293 and rat pituitary GH3 cell lines, human tumors and in transgenic mice with elevated somatotrope Gpr101 expression driven by the rat Ghrhr promoter (GhrhrGpr101). Here, we report that Gpr101 causes elevated GH/prolactin secretion in transgenic GhrhrGpr101 mice but without hyperplasia/tumorigenesis. We show that GPR101 constitutively activates not only Gs, but also Gq/11 and G12/13, which leads to GH secretion but not proliferation. These signatures of GPR101 signaling, notably PKC activation, are also present in human pituitary tumors with high GPR101 expression. These results underline a role for GPR101 in the regulation of somatotrope axis function.
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5
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Granata R. Peripheral activities of growth hormone-releasing hormone. J Endocrinol Invest 2016; 39:721-7. [PMID: 26891937 DOI: 10.1007/s40618-016-0440-x] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/18/2015] [Accepted: 02/03/2016] [Indexed: 12/21/2022]
Abstract
Growth hormone (GH)-releasing hormone (GHRH) is produced by the hypothalamus and stimulates GH synthesis and release in the anterior pituitary gland. In addition to its endocrine role, GHRH exerts a wide range of extrapituitary effects which include stimulation of cell proliferation, survival and differentiation, and inhibition of apoptosis. Accordingly, expression of GHRH, as well as the receptor GHRH-R and its splice variants, has been demonstrated in different peripheral tissues and cell types. Among the direct peripheral activities, GHRH regulates pancreatic islet and β-cell survival and function and endometrial cell proliferation, promotes cardioprotection and wound healing, influences the immune and reproductive systems, reduces inflammation, indirectly increases lifespan and adiposity and acts on skeletal muscle cells to inhibit cell death and atrophy. Therefore, it is becoming increasingly clear that GHRH exerts important extrapituitary functions, suggesting potential therapeutic use of the peptide and its analogs in a wide range of medical settings.
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Affiliation(s)
- R Granata
- Lab of Molecular and Cellular Endocrinology, Division of Endocrinology, Diabetes and Metabolism, Department of Medical Sciences, University of Torino, Corso Dogliotti, 14, 10126, Turin, Italy.
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Beneficial effects of growth hormone-releasing hormone agonists on rat INS-1 cells and on streptozotocin-induced NOD/SCID mice. Proc Natl Acad Sci U S A 2015; 112:13651-6. [PMID: 26474831 DOI: 10.1073/pnas.1518540112] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Agonists of growth hormone-releasing hormone (GHRH) have been previously reported to promote growth, function, and engraftment of islet cells following transplantation. Here we evaluated recently synthesized GHRH agonists on the proliferation and biological functions of rat pancreatic β-cell line (INS-1) and islets. In vitro treatment of INS-1 cells with GHRH agonists increased cell proliferation, the expression of cellular insulin, insulin-like growth factor-1 (IGF1), and GHRH receptor, and also stimulated insulin secretion in response to glucose challenge. Exposure of INS-1 cells to GHRH agonists, MR-356 and MR-409, induced activation of ERK and AKT pathways. Agonist MR-409 also significantly increased the levels of cellular cAMP and the phosphorylation of cAMP response element binding protein (CREB) in INS-1 cells. Treatment of rat islets with agonist, MR-409 significantly increased cell proliferation, islet size, and the expression of insulin. In vivo daily s.c. administration of 10 μg MR-409 for 3 wk dramatically reduced the severity of streptozotocin (STZ)-induced diabetes in nonobese diabetic severe combined immunodeficiency (NOD/SCID) mice. The maximal therapeutic benefits with respect to the efficiency of engraftment, ability to reach normoglycemia, gain in body weight, response to high glucose challenge, and induction of higher levels of serum insulin and IGF1 were observed when diabetic mice were transplanted with rat islets preconditioned with GHRH agonist, MR-409, and received additional treatment with MR-409 posttransplantation. This study provides an improved approach to the therapeutic use of GHRH agonists in the treatment of diabetes mellitus.
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7
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A hypothesis for a possible synergy between ghrelin and exercise in patients with cachexia: Biochemical and physiological bases. Med Hypotheses 2015; 85:927-33. [PMID: 26404870 DOI: 10.1016/j.mehy.2015.09.008] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2014] [Revised: 09/07/2015] [Accepted: 09/07/2015] [Indexed: 12/15/2022]
Abstract
This article reviews the biochemical and physiological observations underpinning the synergism between ghrelin and ghrelin agonists with exercise, especially progressive resistance training that has been shown to increase muscle mass. The synergy of ghrelin agonists and physical exercise could be beneficial in conditions where muscle wasting is present, such as that found in patients with advanced cancer. The principal mechanism that controls muscle anabolism following the activation of the ghrelin receptor in the central nervous system involves the release of growth hormone/insulin-like growth factor-1 (GH/IGF-1). GH/IGF-1 axis has a dual pathway of action on muscle growth: (a) a direct action on muscle, bone and fat tissue and (b) an indirect action via the production of both muscle-restricted mIGF-1 and anti-cachectic cytokines. Progressive resistance training is a potent inducer of the secretion the muscle-restricted IGF-1 (mIGF-1) that enhances protein synthesis, increases lean body mass and eventually leads to the improvement of muscle strength. Thus, the combination of ghrelin administration with progressive resistance training may serve to circumvent ghrelin resistance and further reduce muscle wasting, which are commonly associated with cachexia.
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8
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Zeng P, Chen JX, Yang B, Zhi X, Guo FX, Sun ML, Wang JL, Wei J. Attenuation of systemic morphine-induced analgesia by central administration of ghrelin and related peptides in mice. Peptides 2013; 50:42-9. [PMID: 24113541 DOI: 10.1016/j.peptides.2013.09.017] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/01/2013] [Revised: 09/27/2013] [Accepted: 09/27/2013] [Indexed: 12/28/2022]
Abstract
Ghrelin, an acylated 28-amino peptide secreted in the gastric endocrine cells, has been demonstrated to stimulate the release of growth hormone, increase food intake, and inhibit pro-inflammatory cascade, etc. Ghrelin mainly combines with its receptor (GHS-R1α) to play the role in physiological and pathological functions. It has been reported that ghrelin plays important roles in the control of pain through interaction with the opioid system in inflammatory pain and acute pain. However, very few studies show the effect of supraspinal ghrelin system on antinociception induced by intraperitoneal (i.p.) administration of morphine. In the present study, intracerebroventricular (i.c.v.) injection of ghrelin (0.1, 1, 10 and 100 nmol/L) produced inhibition of systemic morphine (6 mg/kg, i.p.) analgesia in the tail withdrawal test. Similarly, i.c.v. injection GHRP-6 and GHRP-2 which are the agonists of GHS-R1α, also decreased analgesia effect induced by morphine injected intraperitoneally in mice. Furthermore, these anti-opioid activities of ghrelin and related peptides were not blocked by pretreatment with the GHS-R1α selective antagonist [d-Lys(3)]-GHRP-6 (100 nmol/L, i.c.v.). These results demonstrated that central ghrelin and related peptides could inhibit the analgesia effect induced by intraperitoneal (i.p.) administration of morphine. The anti-opioid effects of ghrelin and related peptides do not interact with GHS-R1a. These findings may pave the way for a new strategy on investigating the interaction between ghrelin system and opioids on pain modulation.
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Affiliation(s)
- Ping Zeng
- Department of Physiology, Medical College of Nanchang University, Bayi Road 461, Nanchang, Jiangxi 330006, China
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9
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Schellekens H, Dinan TG, Cryan JF. Taking two to tango: a role for ghrelin receptor heterodimerization in stress and reward. Front Neurosci 2013; 7:148. [PMID: 24009547 PMCID: PMC3757321 DOI: 10.3389/fnins.2013.00148] [Citation(s) in RCA: 63] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2013] [Accepted: 08/01/2013] [Indexed: 12/25/2022] Open
Abstract
The gut hormone, ghrelin, is the only known peripherally derived orexigenic signal. It activates its centrally expressed receptor, the growth hormone secretagogue receptor (GHS-R1a), to stimulate food intake. The ghrelin signaling system has recently been suggested to play a key role at the interface of homeostatic control of appetite and the hedonic aspects of food intake, as a critical role for ghrelin in dopaminergic mesolimbic circuits involved in reward signaling has emerged. Moreover, enhanced plasma ghrelin levels are associated with conditions of physiological stress, which may underline the drive to eat calorie-dense "comfort-foods" and signifies a role for ghrelin in stress-induced food reward behaviors. These complex and diverse functionalities of the ghrelinergic system are not yet fully elucidated and likely involve crosstalk with additional signaling systems. Interestingly, accumulating data over the last few years has shown the GHS-R1a receptor to dimerize with several additional G-protein coupled receptors (GPCRs) involved in appetite signaling and reward, including the GHS-R1b receptor, the melanocortin 3 receptor (MC3), dopamine receptors (D1 and D2), and more recently, the serotonin 2C receptor (5-HT2C). GHS-R1a dimerization was shown to affect downstream signaling and receptor trafficking suggesting a potential novel mechanism for fine-tuning GHS-R1a receptor mediated activity. This review summarizes ghrelin's role in food reward and stress and outlines the GHS-R1a dimer pairs identified to date. In addition, the downstream signaling and potential functional consequences of dimerization of the GHS-R1a receptor in appetite and stress-induced food reward behavior are discussed. The existence of multiple GHS-R1a heterodimers has important consequences for future pharmacotherapies as it significantly increases the pharmacological diversity of the GHS-R1a receptor and has the potential to enhance specificity of novel ghrelin-targeted drugs.
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Wei J, Zhi X, Wang XL, Zeng P, Zou T, Yang B, Wang JL. In vivo characterization of the effects of ghrelin on the modulation of acute pain at the supraspinal level in mice. Peptides 2013; 43:76-82. [PMID: 23500519 DOI: 10.1016/j.peptides.2013.03.004] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/04/2013] [Revised: 03/04/2013] [Accepted: 03/04/2013] [Indexed: 12/12/2022]
Abstract
Ghrelin, an acylated peptide produced in the stomach, increases food intake and growth hormone secretion, inhibits pro-inflammatory cascade, etc. Ghrelin and its receptor (GHS-R1a) mRNA were found in the area related to the regions for controlling pain transmission, such as the hypothalamus, the midbrain, the spinal cord, etc. Ghrelin has been shown to have antinociceptive activity and also anti-inflammatory properties in inflammatory pain and chronic neuropathic pain. Therefore, the aim of the present study was to investigate the effects of ghrelin for the first time in the acute pain modulation at the supraspinal level, using the tail withdrawal test and hot-plate test in mice. Intracerebroventricular (i.c.v.) administration of ghrelin (mouse, 0.1-3 nmol) produced a dose- and time-related antinociceptive effect in the tail withdrawal test and hot-plate test, respectively. Antinociceptive effect elicited by ghrelin (i.c.v., 1 nmol) was significantly antagonized by opioid receptor antagonist naloxone (i.c.v., 10 nmol co-injection or i.p., 10mg/kg, 10 min prior to ghrelin) in both tail withdrawal test and hot-plate test. At these doses, naloxone significantly antagonized the antinociceptive effect induced by morphine (i.c.v., 3 nmol). Ghrelin (i.c.v., 1 nmol)-induced antinociception was significantly antagonized by co-injection with 10 nmol [d-Lys3]-GHRP-6, the selective antagonist of GHS-R1a identified more recently, while [d-Lys3]-GHRP-6 (10 nmol) alone induced neither hyperalgesia nor antinociception. Overall this data indicate that ghrelin could produce antinociception through an interaction with GHS-R1a and with the central opioid system. Thus ghrelin may be a promising peptide for developing new analgesic drugs.
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Affiliation(s)
- Jie Wei
- Department of Physiology, Medical College of Nanchang University, Bayi Road 461, Nanchang, Jiangxi 330006, China.
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Komatsu M, Kojima M, Okamura H, Nishio M, Kaneda M, Kojima T, Takeda H, Malau-Aduli AEO, Takahashi H. Age-related changes in gene expression of the growth hormone secretagogue and growth hormone-releasing hormone receptors in Holstein-Friesian cattle. Domest Anim Endocrinol 2012; 42:83-93. [PMID: 22056236 DOI: 10.1016/j.domaniend.2011.09.006] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/16/2011] [Revised: 09/23/2011] [Accepted: 09/26/2011] [Indexed: 10/15/2022]
Abstract
Growth hormone secretion from the anterior pituitary gland is controlled by interactions between three hormone receptors, between GHRH and GHRH receptor (GHRH-R), between ghrelin and growth hormone secretagogue receptor (GHS-R1a), and between somatostatin and somatostatin receptors in the hypothalamus and anterior pituitary gland. Ghrelin-GHS-R1a is involved in many important functions, including GH secretion and appetite. We investigated age-related changes in the expressions of GHS-R1a, GHS-R1b (the truncated-type receptor), and GHRH-R mRNAs by real-time reverse transcription-PCR using 16 tissues, leukocytes, oocytes, and cumulus cells in Holstein-Friesian cattle. The tissue samples were divided into three age classes: 1) 19 to 26 d of age (preweaning calves), 2) 2 mo to 6.5 mo of age (postweaning calves), and 3) 3.2 to 8.1 yr of age (cows). The GHS-R1a mRNA was highly (P < 0.05) expressed in the arcuate nucleus, pituitary gland, and liver compared with that of the other tissues in all age classes. Expression of GHS-R 1a mRNA in the arcuate nucleus of postweaning calves was > 10-fold greater (P < 0.01) than those of preweaning calves and cows, and its expression level was the greatest (P < 0.01) in all tissues examined in age group 2. GHS-R1a and GHRH-R mRNA expressions in the pituitary gland of preweaning calves tended to be greater (P < 0.20 and P < 0.17, respectively) than those of postweaning calves and cows. GHS-R1b mRNA expression was detected in all tissues examined, and abundance was greater (P < 0.05) in the pancreas, pituitary gland, spleen, arcuate nucleus, adipose tissue, and leukocyte compared with that of the other tissues examined in age group 3. Interestingly, a relatively large animal-to-animal variation was observed in pancreas GHS-R 1b mRNA expression. The GHRH-R mRNA was markedly increased (P < 0.01) in the pituitary gland in all age groups compared with that of the other tissues. GHRH-R mRNA abundance in the arcuate nucleus, pituitary gland, liver, spleen, adipose tissue, and heart of preweaning calves tended to be greater than those of postweaning calves and cows. The GHRH-R mRNA was not detected in the mammary gland and adipose tissue of nonlactating cows.
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MESH Headings
- Age Factors
- Animals
- Arcuate Nucleus of Hypothalamus/physiology
- Cattle/genetics
- Cattle/metabolism
- Female
- Gene Expression Regulation
- Growth Hormone/biosynthesis
- Growth Hormone/genetics
- Growth Hormone/metabolism
- Least-Squares Analysis
- Male
- Pituitary Gland, Anterior/metabolism
- Pituitary Gland, Anterior/physiology
- RNA, Messenger/biosynthesis
- RNA, Messenger/genetics
- Real-Time Polymerase Chain Reaction/veterinary
- Receptors, Ghrelin/biosynthesis
- Receptors, Ghrelin/genetics
- Receptors, Neuropeptide/biosynthesis
- Receptors, Neuropeptide/genetics
- Receptors, Pituitary Hormone-Regulating Hormone/biosynthesis
- Receptors, Pituitary Hormone-Regulating Hormone/genetics
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Affiliation(s)
- M Komatsu
- National Institute of Livestock and Grassland Science, Ikenodai 2, Tsukuba, Ibaraki 305-0901, Japan.
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Peroni CN, Hayashida CY, Nascimento N, Longuini VC, Toledo RA, Bartolini P, Bowers CY, Toledo SPA. Growth hormone response to growth hormone-releasing peptide-2 in growth hormone-deficient little mice. Clinics (Sao Paulo) 2012; 67:265-72. [PMID: 22473409 PMCID: PMC3297037 DOI: 10.6061/clinics/2012(03)11] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/16/2011] [Accepted: 12/15/2011] [Indexed: 11/18/2022] Open
Abstract
OBJECTIVE To investigate a possible direct, growth hormone-releasing, hormone-independent action of a growth hormone secretagogue, GHRP-2, in pituitary somatotroph cells in the presence of inactive growth hormone-releasing hormone receptors. MATERIALS AND METHODS The responses of serum growth hormone to acutely injected growth hormone-releasing P-2 in lit/lit mice, which represent a model of GH deficiency arising from mutated growth hormone-releasing hormone-receptors, were compared to those observed in the heterozygous (lit/+) littermates and wild-type (+/+) C57BL/6J mice. RESULTS After the administration of 10 mcg of growth hormone-releasing P-2 to lit/lit mice, a growth hormone release of 9.3±1.5 ng/ml was observed compared with 1.04±1.15 ng/ml in controls (p<0.001). In comparison, an intermediate growth hormone release of 34.5±9.7 ng/ml and a higher growth hormone release of 163±46 ng/ml were induced in the lit/+ mice and wild-type mice, respectively. Thus, GHRP-2 stimulated growth hormone in the lit/lit mice, and the release of growth hormone in vivo may be only partially dependent on growth hormone-releasing hormone. Additionally, the plasma leptin and ghrelin levels were evaluated in the lit/lit mice under basal and stimulated conditions. CONCLUSIONS Here, we have demonstrated that lit/lit mice, which harbor a germline mutation in the Growth hormone-releasing hormone gene, maintain a limited but statistically significant growth hormone elevation after exogenous stimulation with GHRP-2. The present data probably reflect a direct, growth hormone-independent effect on Growth hormone S (ghrelin) stimulation in the remaining pituitary somatotrophs of little mice that is mediated by growth hormone S-R 1a.
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Affiliation(s)
- Cibele N Peroni
- Biotechnology Department, National Nuclear Energy Commission, Cidade Universitária, São Paulo, SP, Brazil
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Grey CL, Chang JP. Differential involvement of protein kinase C and protein kinase A in ghrelin-induced growth hormone and gonadotrophin release from goldfish (Carassius auratus) pituitary cells. J Neuroendocrinol 2011; 23:1273-87. [PMID: 21919972 DOI: 10.1111/j.1365-2826.2011.02221.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Ghrelin (GRLN) and its receptor have been identified and characterised in goldfish brain and the pituitary, and recent evidence shows that goldfish (g)GRLN(19) induces both growth hormone (GH) and maturational gonadotrophin (LH) release through an extracellular Ca(2+) -dependent mechanism in goldfish. To further understand the role of GRLN in hormone release, the present study examined the involvement of protein kinase C (PKC) and protein kinase A (PKA) in gGRLN(19) -induced GH and LH release and corresponding Ca(2+) signals in primary cultures of goldfish pituitary cells. Treatments with PKC inhibitors, Bis-II and Gö 6976, significantly reduced gGRLN(19) -induced GH and LH release and their corresponding intracellular Ca(2+) signals in identified somatotrophs and gonadotrophs, respectively. gGRLN(19) was unable to further stimulate hormone release or Ca(2+) signals when cells were pretreated with the PKC agonist, DiC8. PKA inhibitors, H-89 and KT 5720, inhibited gGRLN(19) -induced LH release and Ca(2+) signals in gonadotrophs but not GH release or Ca(2+) signals in somatotrophs. Interestingly, pretreatment of pituitary cells with the adenylate cyclase activator forskolin potentiated gGRLN(19) -induced GH, but not LH, release, although it had no effect on intracellular Ca(2+) signals in either cell type. Taken together, the results suggest that PKC is an important intracellular component in gGRLN(19) -induced GH and LH release, whereas PKA is involved in gGRLN(19) -elicited LH release. Furthermore, the PKA pathway potentiates gGRLN(19) -induced GH release via a Ca(2+) -independent mechanism. Overall, the present study provides insight into the neuroendocrine regulation of GH and LH release by elucidating the mechanistic aspects of GRLN, a hormone involved in many critical physiological processes, including pituitary functions.
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Affiliation(s)
- C L Grey
- Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada
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The endocrine regulation network of growth hormone synthesis and secretion in fish: Emphasis on the signal integration in somatotropes. SCIENCE CHINA-LIFE SCIENCES 2010; 53:462-70. [DOI: 10.1007/s11427-010-0084-6] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/23/2009] [Accepted: 01/06/2010] [Indexed: 01/21/2023]
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Veldhuis JD, Bowers CY. Integrating GHS into the Ghrelin System. INTERNATIONAL JOURNAL OF PEPTIDES 2010; 2010:879503. [PMID: 20798846 PMCID: PMC2925380 DOI: 10.1155/2010/879503] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/24/2009] [Accepted: 12/30/2009] [Indexed: 12/21/2022]
Abstract
Oligopeptide derivatives of metenkephalin were found to stimulate growth-hormone (GH) release directly by pituitary somatotrope cells in vitro in 1977. Members of this class of peptides and nonpeptidyl mimetics are referred to as GH secretagogues (GHSs). A specific guanosine triphosphatate-binding protein-associated heptahelical transmembrane receptor for GHS was cloned in 1996. An endogenous ligand for the GHS receptor, acylghrelin, was identified in 1999. Expression of ghrelin and homonymous receptor occurs in the brain, pituitary gland, stomach, endothelium/vascular smooth muscle, pancreas, placenta, intestine, heart, bone, and other tissues. Principal actions of this peptidergic system include stimulation of GH release via combined hypothalamopituitary mechanisms, orexigenesis (appetitive enhancement), insulinostasis (inhibition of insulin secretion), cardiovascular effects (decreased mean arterial pressure and vasodilation), stimulation of gastric motility and acid secretion, adipogenesis with repression of fat oxidation, and antiapoptosis (antagonism of endothelial, neuronal, and cardiomyocyte death). The array of known and proposed interactions of ghrelin with key metabolic signals makes ghrelin and its receptor prime targets for drug development.
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Affiliation(s)
- Johannes D. Veldhuis
- Department of Medicine, Endocrine Research Unit, Mayo School of Graduate Medical Education, Clinical Translational Science Center, Mayo Clinic, Rochester, MN 55905, USA
| | - Cyril Y. Bowers
- Division of Endocrinology, Department of Internal Medicine, Tulane University Health Sciences Center, New Orleans, LA 70112, USA
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Sheriff S, Joshi R, Friend LA, James JH, Balasubramaniam A. Ghrelin receptor agonist, GHRP-2, attenuates burn injury-induced MuRF-1 and MAFbx expression and muscle proteolysis in rats. Peptides 2009; 30:1909-13. [PMID: 19577604 DOI: 10.1016/j.peptides.2009.06.029] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/04/2009] [Revised: 06/24/2009] [Accepted: 06/24/2009] [Indexed: 10/20/2022]
Abstract
Thermal injury results in hypermetabolism, loss of body weight, and skeletal muscle wasting in mice and rats. Our earlier studies have demonstrated that ghrelin injection stimulates food intake and growth hormone release and inhibits skeletal muscle proteolysis in rats with thermal injury. We sought to develop a lower molecular weight, stable and longer acting peptide to combat the catabolic responses caused by thermal injury. Towards this goal, we examined the role of the hexapeptide mimetic of ghrelin, growth hormone-releasing peptide-2 (GHRP-2), on expression of E3 ubiquitin ligases and breakdown of muscle protein in rats with thermal injury. Slow in vivo release of GHRP-2 through minipump for 24h attenuated the thermal injury-induced increase in mRNA expression of IL-6 and of the E3 ubiquitin ligases, MuRF-1 and MAFbx, in rat skeletal muscle. Furthermore, burn-induced increases in total and myofibrillar protein breakdown from rat EDL muscle were attenuated by GHRP-2. These findings suggest that catabolic responses resulting from thermal injury can be attenuated by GHRP-2.
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Affiliation(s)
- Sulaiman Sheriff
- Department of Surgery, University of Cincinnati College of Medicine, and Shriners Hospital for Children, 231 Albert Sabin Way, Cincinnati, OH 45267-0558, USA
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Abstract
The fight against doping in sport using analytical chemistry is a mature area with a history of approximately 100 years in horse racing and at least 40 years in human sport. Over that period, the techniques used and the breadth of coverage have developed significantly. These improvements in the testing methods have been matched by the increased sophistication of the methods, drugs and therapies available to the cheat and, as a result, testing has been a reactive process constantly adapting to meet new threats. Following the inception of the World Anti-Doping Agency, research into the methods and technologies available for human doping control have received coordinated funding on an international basis. The area of biomarker research has been a major beneficiary of this funding. The aim of this article is to review recent developments in the application of biomarkers to doping control and to assess the impact this could make in the future.
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Schellekens H, Dinan TG, Cryan JF. Lean mean fat reducing "ghrelin" machine: hypothalamic ghrelin and ghrelin receptors as therapeutic targets in obesity. Neuropharmacology 2009; 58:2-16. [PMID: 19573543 DOI: 10.1016/j.neuropharm.2009.06.024] [Citation(s) in RCA: 87] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2009] [Revised: 06/18/2009] [Accepted: 06/19/2009] [Indexed: 12/13/2022]
Abstract
Obesity has reached epidemic proportions not only in Western societies but also in the developing world. Current pharmacological treatments for obesity are either lacking in efficacy and/or are burdened with adverse side effects. Thus, novel strategies are required. A better understanding of the intricate molecular pathways controlling energy homeostasis may lead to novel therapeutic intervention. The circulating hormone, ghrelin represents a major target in the molecular signalling regulating food intake, appetite and energy expenditure and its circulating levels often display aberrant signalling in obesity. Ghrelin exerts its central orexigenic action mainly in the hypothalamus and in particular in the arcuate nucleus via activation of specific G-protein coupled receptors (GHS-R). In this review we describe current pharmacological models of how ghrelin regulates food intake and how manipulating ghrelin signalling may give novel insight into developing better and more selective anti-obesity drugs. Accumulating data suggests multiple ghrelin variants and additional receptors exist to play a role in energy metabolism and these may well play an important role in obesity. In addition, the recent findings of hypothalamic GHS-R crosstalk and heterodimerization may add to the understanding of the complexity of bodyweight regulation.
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Lorenzi T, Meli R, Marzioni D, Morroni M, Baragli A, Castellucci M, Gualillo O, Muccioli G. Ghrelin: a metabolic signal affecting the reproductive system. Cytokine Growth Factor Rev 2009; 20:137-52. [DOI: 10.1016/j.cytogfr.2009.02.003] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
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20
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Growth hormone-releasing hormone as an agonist of the ghrelin receptor GHS-R1a. Proc Natl Acad Sci U S A 2008; 105:20452-7. [PMID: 19088192 DOI: 10.1073/pnas.0811680106] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Ghrelin synergizes with growth hormone-releasing hormone (GHRH) to potentiate growth hormone (GH) response through a mechanism not yet fully characterized. This study was conducted to analyze the role of GHRH as a potential ligand of the ghrelin receptor, GHS-R1a. The results show that hGHRH(1-29)NH(2) (GHRH) induces a dose-dependent calcium mobilization in HEK 293 cells stably transfected with GHS-R1a an effect not observed in wild-type HEK 293 cells. This calcium rise is also observed using the GHRH receptor agonists JI-34 and JI-36. Radioligand binding and cross-linking studies revealed that calcium response to GHRH is mediated by the ghrelin receptor GHS-R1a. GHRH activates the signaling route of inositol phosphate and potentiates the maximal response to ghrelin measured in inositol phosphate turnover. The presence of GHRH increases the binding capacity of (125)I-ghrelin in a dose dependent-fashion showing a positive binding cooperativity. In addition, confocal microscopy in CHO cells transfected with GHS-R1a tagged with enhanced green fluorescent protein shows that GHRH activates the GHS-R1a endocytosis. Furthermore, the selective GHRH-R antagonists, JV-1-42 and JMR-132, act also as antagonists of the ghrelin receptor GHS-R1a. Our findings suggest that GHRH interacts with ghrelin receptor GHS-R1a, and, in consequence, modifies the ghrelin-associated intracellular signaling pathway. This interaction may represent a form of regulation, which could play a putative role in the physiology of GH regulation and appetite control.
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21
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Park YJ, Lee YJ, Kim SH, Joung DS, Kim BJ, So I, Park DJ, Cho BY. Ghrelin enhances the proliferating effect of thyroid stimulating hormone in FRTL-5 thyroid cells. Mol Cell Endocrinol 2008; 285:19-25. [PMID: 18313206 DOI: 10.1016/j.mce.2008.01.003] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/19/2007] [Revised: 01/07/2008] [Accepted: 01/10/2008] [Indexed: 11/16/2022]
Abstract
Ghrelin regulates cell proliferation through the growth hormone secretagogue receptor (GHS-R). We confirmed the expression of GHS-R in FRTL-5 thyroid cells and investigated the effects of ghrelin in thyrocytes using FRTL-5 cells. Ghrelin increased intracellular calcium levels but not intracellular cyclic AMP levels. Ghrelin activated Erk within 2min, then activated Akt and STAT3. Erk phosphorylation was inhibited by the calcium inhibitor cyclopiazonic acid (CPA). Ghrelin alone did not stimulate FRTL-5 cell proliferation but enhanced the effects of thyroid stimulating hormone (TSH). Pretreatment with TSH potentiates the growth effects of ghrelin in thyroid cells, and p66Shc, a growth factor receptor adaptor protein, might mediate these synergistic effects. Ghrelin phosphorylated TSH-induced p66Shc, which was inhibited by CPA. Ghrelin did not affect the proliferation of ARO cells, which showed no increased expression of p66Shc after TSH treatment. Thus, ghrelin-induced intracellular calcium signaling enhanced the TSH-induced proliferation of thyrocytes, possibly mediated by the p66Shc pathway.
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Affiliation(s)
- Young Joo Park
- Department of Internal Medicine, Seoul National University College of Medicine, 28 Yeongeon-dong, Jongno-gu, Seoul, Republic of Korea
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22
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Leite-Moreira AF, Rocha-Sousa A, Henriques-Coelho T. Cardiac, skeletal, and smooth muscle regulation by ghrelin. VITAMINS AND HORMONES 2008; 77:207-38. [PMID: 17983858 DOI: 10.1016/s0083-6729(06)77009-1] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Ghrelin, mainly secreted from gastric mucosa, is the endogenous ligand for the growth hormone secretagogue receptor and induces a potent release of growth hormone. Ghrelin is widely expressed in different tissues and therefore has both endocrine and paracrine/autocrine effects. In this chapter, we summarize: (1) structure and distribution of ghrelin and its receptors; (2) myocardial effects of ghrelin, describing its acute and chronic actions on cardiac function; (3) ghrelin effects on smooth muscle, namely vascular smooth muscle, intraocular and gastrointestinal smooth muscle; and (4) skeletal actions of ghrelin. Ghrelin has a potent vasodilator effect, thereby reducing cardiac afterload and increasing cardiac output. In models of heart failure and myocardial ischemia, ghrelin administration has beneficial effects. At smooth muscle, ghrelin modulates vascular tone, increases gut transit, and relaxes iris muscles. In the skeletal muscle, ghrelin regulates resting membrane potential. In conclusion, there are increasing evidences that ghrelin is a peptide with paracrine actions that can modulate cardiac, smooth, and skeletal muscle functions.
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Affiliation(s)
- Adelino F Leite-Moreira
- Department of Physiology, Faculty of Medicine, University of Porto, Alameda Professor Hernâni Monteiro, 4200-319, Porto, Portugal
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23
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Kineman RD, Luque RM. Evidence that ghrelin is as potent as growth hormone (GH)-releasing hormone (GHRH) in releasing GH from primary pituitary cell cultures of a nonhuman primate (Papio anubis), acting through intracellular signaling pathways distinct from GHRH. Endocrinology 2007; 148:4440-9. [PMID: 17540720 DOI: 10.1210/en.2007-0441] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Ghrelin is more effective than GHRH in stimulating GH release in normal adult humans and monkeys in vivo. This robust effect of ghrelin has been largely attributed to regulation of hypothalamic input, whereas the direct effect of ghrelin on pituitary GH release has been minimized by the observation that ghrelin has only a modest impact on GH release, compared with GHRH, in cultures prepared from human fetal pituitaries and GH-producing adenomas, as well as pituitaries from nonprimate species. However, comparable in vitro studies have not been performed to test the direct effect of ghrelin on normal adult primates. Therefore, in the present study, primary pituitary cell cultures from female baboons (Papio anubis) were used as a model system to test the direct effects of ghrelin on primate somatotrope function. In this model, both ghrelin and GHRH increased GH release in a dose-dependent fashion. Surprisingly, at maximal concentrations (10 nM), both ghrelin and GHRH elicited a robust increase in GH release (4 and 24 h, respectively), and both up-regulated GH secretagogue-receptor and GHRH-receptor mRNA levels (24 h). Combined treatment with ghrelin and GHRH resulted in an additive effect on GH release, suggesting that distinct intracellular signaling pathways are activated by each ligand, as confirmed by the use of specific inhibitors of intracellular signaling. Together, these results present the first evidence that a direct effect of ghrelin on somatotrope function may play a major role in stimulating GH release in primates.
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Affiliation(s)
- Rhonda D Kineman
- Section of Endocrinology, Diabetes and Metabolism, Department of Medicine, University of Illinois at Chicago, Chicago, IL, USA
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Rocha-Sousa A, Henriques-Coelho T, Leite-Moreira AF. Potential role of the growth hormone secretagogues in clinical practice. Expert Opin Ther Pat 2007. [DOI: 10.1517/13543776.17.8.909] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
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Kohno D, Nakata M, Maekawa F, Fujiwara K, Maejima Y, Kuramochi M, Shimazaki T, Okano H, Onaka T, Yada T. Leptin suppresses ghrelin-induced activation of neuropeptide Y neurons in the arcuate nucleus via phosphatidylinositol 3-kinase- and phosphodiesterase 3-mediated pathway. Endocrinology 2007; 148:2251-63. [PMID: 17303662 DOI: 10.1210/en.2006-1240] [Citation(s) in RCA: 89] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Neuropeptide Y (NPY) neurons in the hypothalamic arcuate nucleus (ARC) play a central role in stimulation of feeding. They sense and integrate peripheral and central signals, including ghrelin and leptin. However, the mechanisms of interaction of these hormones in NPY neurons are largely unknown. This study explored the interaction and underlying signaling cross talk between ghrelin and leptin in NPY neurons. Cytosolic Ca(2+) concentration ([Ca(2+)](i)) in single neurons isolated from ARC of adult rats was measured by fura-2 microfluorometry. Ghrelin increased [Ca(2+)](i) in 31% of ARC neurons. The [Ca(2+)](i) increases were inhibited by blockers of phospholipase C, adenylate cyclase, and protein kinase A. Ghrelin-induced [Ca(2+)](i) increases were suppressed by subsequent administration of leptin. Fifteen of 18 ghrelin-activated, leptin-suppressed neurons (83%) contained NPY. Leptin suppression of ghrelin responses was prevented by pretreatment with inhibitors of phosphatidylinositol 3-kinase and phosphodiesterase 3 (PDE3) but not MAPK. ATP-sensitive potassium channel inhibitors and activators did not prevent and mimic leptin suppression, respectively. Although leptin phosphorylated signal-transducer and activator of transcription 3 (STAT3) in NPY neurons, neither STAT3 inhibitor nor genetic STAT3 deletion altered leptin suppression of ghrelin responses. Furthermore, orexigenic effect of intracerebroventricular ghrelin in rats was counteracted by leptin in a PDE3-dependent manner. These findings indicate that ghrelin increases [Ca(2+)](i) via mechanisms depending on phospholipase C and adenylate cyclase-PKA pathways in ARC NPY neurons and that leptin counteracts ghrelin responses via a phosphatidylinositol 3-kinase-PDE3 pathway. This interaction may play an important role in regulating ARC NPY neuron activity and, thereby, feeding.
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Affiliation(s)
- Daisuke Kohno
- Department of Physiology, Division of Integrative Physiology, Jichi Medical University, School of Medicine, Tochigi 329-0498, Japan
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Sirotkin AV, Grossmann R. The role of ghrelin and some intracellular mechanisms in controlling the secretory activity of chicken ovarian cells. Comp Biochem Physiol A Mol Integr Physiol 2007; 147:239-46. [PMID: 17293148 DOI: 10.1016/j.cbpa.2006.12.038] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2006] [Revised: 12/28/2006] [Accepted: 12/30/2006] [Indexed: 10/23/2022]
Abstract
The general aim of these in-vitro experiments was to determine whether ghrelin controls the secretory activity of chicken ovarian cells and whether its action is mediated by TK-, MAPK-, CDK- or PKA-dependent intracellular mechanisms. We postulated that particular protein kinases could be considered as mediators of ghrelin action (a) if they are controlled by ghrelin, and (b) if blockers of these kinases modify the action of ghrelin. In our in-vitro experiments we investigated whether ghrelin altered the accumulation of TK, MAPK, CDK and PKA in chicken ovarian cells and whether ghrelin, with or without blockers of MAPK, CDK and PKA, affected the secretion of progesterone (P4), testosterone (T), estradiol (E2) or arginine-vasotocin (AVT). In the first series of experiments, the influence of a ghrelin 1-18 analogue (1, 10 or 100 ng/mL) was studied on the expression of TK, MAPK and PKA in cultured chicken ovarian granulosa cells. The percentage of cells containing TK/phosphotyrosine MAPK/ERK1, 2 and PKA was determined using immunocytochemistry. Ghrelin increased the expression of both TK and MAPK. The low concentration of ghrelin (1 ng/mL) increased the accumulation of PKA in ovarian cells whilst the high concentration (100 ng/mL) decreased it. The 10 ng/mL concentration had no effect. In the second series of experiments, the effects of the ghrelin analogue combined with an MAPK blocker (PD98059; 100 ng/mL), a CDK blocker (olomoucine; 1 microg/mL), or a PKA blocker (KT5720; 100 ng/mL), were tested for their effects on the secretion of hormones by cultured fragments of chicken ovarian follicular wall. P4, T, E2 and AVT secretions were measured using RIA and EIA. Ghrelin increased T and decreased E2, but did not affect P4 or AVT secretion. The PKA blocker promoted P4 secretion and suppressed E2 and AVT, but did not affect T secretion. It prevented or even reversed the effect of ghrelin on T and E2, but did not modify its effect on AVT secretion. The MAPK blocker enhanced P4 and T and reduced AVT, but did not affect E2 secretion. It was able to prevent or reverse the effect of ghrelin on T and E, and it induced a stimulatory effect of ghrelin on AVT secretion. The CDK blocker reduced the secretion of AVT, but had no effect on steroid hormone secretion. It induced the stimulatory influence of ghrelin on the secretion of P4 and AVT, but did not modify the effect of ghrelin on other hormones. These observations clearly demonstrate that ghrelin is a potent regulator of the secretory activity of ovarian cells and of TK, MAPK and PKA. Furthermore, they suggest that MAPK-, CDK- and PKA-dependent intracellular mechanisms are involved in the control of ovarian secretion and that they mediate the effects of ghrelin on these processes.
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Affiliation(s)
- A V Sirotkin
- Research Institute of Animal Production, Hlohovská 2, 949 92 Nitra, Slovakia.
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Muccioli G, Baragli A, Granata R, Papotti M, Ghigo E. Heterogeneity of ghrelin/growth hormone secretagogue receptors. Toward the understanding of the molecular identity of novel ghrelin/GHS receptors. Neuroendocrinology 2007; 86:147-64. [PMID: 17622734 DOI: 10.1159/000105141] [Citation(s) in RCA: 82] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/05/2007] [Accepted: 05/21/2007] [Indexed: 12/23/2022]
Abstract
Ghrelin is a gastric polypeptide displaying strong GH-releasing activity by activation of the type 1a GH secretagogue receptor (GHS-R1a) located in the hypothalamus-pituitary axis. GHS-R1a is a G-protein-coupled receptor that, upon the binding of ghrelin or synthetic peptidyl and non-peptidyl ghrelin-mimetic agents known as GHS, preferentially couples to G(q), ultimately leading to increased intracellular calcium content. Beside the potent GH-releasing action, ghrelin and GHS influence food intake, gut motility, sleep, memory and behavior, glucose and lipid metabolism, cardiovascular performances, cell proliferation, immunological responses and reproduction. A growing body of evidence suggests that the cloned GHS-R1a alone cannot be the responsible for all these effects. The cloned GHS-R1b splice variant is apparently non-ghrelin/GHS-responsive, despite demonstration of expression in neoplastic tissues responsive to ghrelin not expressing GHS-R1a; GHS-R1a homologues sensitive to ghrelin are capable of interaction with GHS-R1b, forming heterodimeric species. Furthermore, GHS-R1a-deficient mice do not show evident abnormalities in growth and diet-induced obesity, suggesting the involvement of another receptor. Additional evidence of the existence of another receptor is that ghrelin and GHS do not always share the same biological activities and activate a variety of intracellular signalling systems besides G(q). The biological actions on the heart, adipose tissue, pancreas, cancer cells and brain shared by ghrelin and the non-acylated form of ghrelin (des-octanoyl ghrelin), which does not bind GHS-R1a, represent the best evidence for the existence of a still unknown, functionally active binding site for this family of molecules. Finally, located in the heart and blood vessels is the scavenger receptor CD36, involved in the endocytosis of the pro-atherogenic oxidized low-density lipoproteins, which is a pharmacologically and structurally distinct receptor for peptidyl GHS and not for ghrelin. This review highlights the most recently discovered features of GHS-R1a and the emerging evidence for a novel group of receptors that are not of the GHS1a type; these appear involved in the transduction of the multiple levels of information provided by GHS and ghrelin.
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Affiliation(s)
- Giampiero Muccioli
- Division of Pharmacology, Department of Anatomy, Pharmacology and Forensic Medicine, University of Turin, Turin, Italy
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Dimaraki EV, Jaffe CA. Role of endogenous ghrelin in growth hormone secretion, appetite regulation and metabolism. Rev Endocr Metab Disord 2006; 7:237-49. [PMID: 17195943 DOI: 10.1007/s11154-006-9022-0] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Ghrelin, a 28-amino acid hormone that is acylated post-translation, is the endogenous ligand for the growth hormone (GH) secretagogue (GHS) receptor (GHS-R). The highest concentrations of ghrelin are found in the stomach; however ghrelin peptide is also present in hypothalamic nuclei known to be important in the control of GH and feeding behavior. Exogenous ghrelin potently stimulates pituitary GH release through a mechanism that is dependent, in part, on endogenous GH-releasing hormone. Whether endogenous ghrelin plays a role in the control of GH secretion and growth is not clear and ghrelin deficient animals appear to grow normally. In contrast, experimental animal and clinical data suggest that abnormalities in GHS-R signaling could impact growth. Ghrelin or other GHS are clinically useful for GH-testing and limited data suggest that they might be useful in the treatment of some patients with GH deficiency. Substantial data have implicated ghrelin as an important regulator of feeding behavior and energy equilibrium. Ghrelin has a potent orexigenic effect in both animals and humans and this effect is mediated through hypothalamic neuropeptide Y (NPY) and Agouti-related peptide (AgRP). Appetite simulation coupled with other metabolic effects promotes weight gain during chronic treatment with ghrelin. These metabolic effects are in part mediated through an increase in respiratory quotient (VQ). Presence of ghrelin appears to be necessary for the development of obesity in some animal models. Whether abnormalities in ghrelin signaling are involved in human obesity is not yet known.
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Affiliation(s)
- Eleni V Dimaraki
- Department of Medicine, Division of Endocrinology and Metabolic Diseases, Evanston Northwestern Healthcare and Northwestern University Feinberg School of Medicine, Evanston, IL 60201, USA
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31
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Chu KM, Chow KBS, Leung PK, Lau PN, Chan CB, Cheng CHK, Wise H. Over-expression of the truncated ghrelin receptor polypeptide attenuates the constitutive activation of phosphatidylinositol-specific phospholipase C by ghrelin receptors but has no effect on ghrelin-stimulated extracellular signal-regulated kinase 1/2 activity. Int J Biochem Cell Biol 2006; 39:752-64. [PMID: 17169600 DOI: 10.1016/j.biocel.2006.11.007] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2006] [Revised: 11/04/2006] [Accepted: 11/17/2006] [Indexed: 11/30/2022]
Abstract
In addition to regulating growth hormone release from the pituitary, ghrelin receptors also influence cell proliferation and apoptosis. By studying mitogen-activated protein kinase activity in human embryonic kidney 293 cells over-expressing ghrelin receptors, we aimed to identify the specific cell signalling pathways used by ghrelin receptors, and to determine if the truncated ghrelin receptor polypeptide had any influence on the functional activity of ghrelin receptors. We found that ghrelin activated extracellular signal-regulated kinases 1/2 with an EC50 value of 10 nM, and that this response was inhibited by the ghrelin receptor antagonists D-Lys3-GHRP-6 and [D-Arg1,D-Phe5,D-Trp(7,9),Leu11]-substance P. Ghrelin had little or no effect on the activity of c-Jun N-terminal kinase, p38 kinase or Akt. Ghrelin appeared to activate extracellular signal-regulated kinases 1/2 through a calcium-independent novel protein kinase C isoform which may utilize diacylglycerol derived from hydrolysis of phosphatidylcholine rather than from phosphatidylinositol. Ghrelin-stimulated extracellular signal-regulated kinases 1/2 activity was independent of transactivation of epidermal growth factor receptors, and even when ghrelin receptor internalization was blocked by concanavalin A or a beta-arrestin mutant, there was no decrease in phosphorylated extracellular signal-regulated kinases 1/2, suggesting this is a G protein-dependent process. The truncated ghrelin receptor polypeptide had no effect on ghrelin receptor signalling to extracellular signal-regulated kinases 1/2, but decreased the constitutive activation of phosphatidylinositol-specific phospholipase C by ghrelin receptors. In conclusion, our results suggest that any up-regulation of the truncated ghrelin receptor polypeptide might preferentially attenuate functional activity dependent on the constitutive activation of ghrelin receptors, while leaving ghrelin-dependent signalling unaffected.
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Affiliation(s)
- Kit-Man Chu
- Department of Pharmacology, Faculty of Medicine, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, SAR, China
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Abstract
Ghrelin is a novel growth hormone (GH)-releasing peptide, isolated from the stomach, which has been identified as an endogenous ligand for the GH secretagogues receptor. The discovery of ghrelin indicates that the release of GH from the pituitary might be regulated, not only by hypothalamic GH-releasing hormone, but also by ghrelin derived from the stomach. Considering the haemodynamic and anabolic effects of GH, ghrelin may have beneficial effects on cardiac function and energy metabolism in heart failure through GH-dependent mechanisms. On the other hand, ghrelin has some GH-independent actions: ghrelin stimulates food intake and induces adiposity. Interestingly, ghrelin acts directly on the CNS to decrease sympathetic nerve activity. It also inhibits apoptosis of cardiomyocytes and endothelial cells. An experimental study has shown that repeated administration of ghrelin improves cardiac structure and function, and attenuates the development of cardiac cachexia in chronic heart failure (CHF). These results suggest that ghrelin has cardiovascular effects and regulates energy metabolism through GH-dependent and -independent mechanisms. Thus, administration of ghrelin may be a new therapeutic strategy for the treatment of severe CHF.
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Affiliation(s)
- Noritoshi Nagaya
- Department of Regenerative Medicine and Tissue Engineering, National Cardiovascular Center Research Institute, Osaka, Japan.
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33
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Roh SG, Doconto M, Feng DD, Chen C. Differential regulation of GHRH-receptor and GHS-receptor expression by long-term in vitro treatment of ovine pituitary cells with GHRP-2 and GHRH. Endocrine 2006; 30:55-62. [PMID: 17185792 DOI: 10.1385/endo:30:1:55] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/21/2005] [Revised: 04/03/2006] [Accepted: 04/10/2006] [Indexed: 11/11/2022]
Abstract
GH secretion is regulated by GHRH and somatostatin via actions on their specific receptors in pituitary somatotropes. Ghrelin and synthetic analogs, GHRPs, also stimulate GH release via GHS-receptors (GHS-R). To examine the long-term effect of GHRH and/or GHRP on somatotropes, primary cultured ovine somatotropes were treated with GHRH (10(-9) and 10(-8) M) and GHRP-2 (10(-8) and 10(-7) M) for up to 2 d. After treatment, culture medium was collected for GH assay, and total RNA was extracted for RT-PCR analysis. To evaluate cell cultures used in this report, somatotrope-enriched pituitary cells were challenged by 6 h GHRH and dexamethasone (DEX) treatment. As expected, GHRH significantly decreased, whereas DEX increased, the levels of GHRHR mRNA. Combined low doses of GHRH (10(-9) M) and GHRP-2 (10(-8) M) treatment for 24 h increased accumulated GH secretion, significantly more than that induced by high doses of GHRH (10(-8) M) and GHRP-2 (10(-7) M). While levels of GHRH-R mRNA increased, GHS-R mRNA levels were decreased by low doses of GHRH and GHRP-2 for 24 h. High doses of GHRH and/or GHRP-2 for 2 d did not increase GH secretion in the second day of treatment and reduced the level of GHRH-R mRNA. High doses of GHRP-2 treatment decreased the levels of both GHRH-R and GHS-R mRNA. Low doses of GHRH and/or GHRP-2 for 2 d increased the level of GHS-R mRNA without changing GHRH-R mRNA levels. Such treatment also increased ghrelin- (10(-9) M) or ghrelin/GHRH (10(-9) M)-induced GH secretion. These results suggest that low doses of GHRP-2 and GHRH prime somatotropes for stimulation by GHRH and ghrelin.
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MESH Headings
- Animals
- Dexamethasone/pharmacology
- Dose-Response Relationship, Drug
- Female
- Ghrelin
- Glucocorticoids/pharmacology
- Growth Hormone/metabolism
- Growth Hormone-Releasing Hormone/pharmacology
- Male
- Oligopeptides/pharmacology
- Peptide Hormones/pharmacology
- RNA, Messenger/biosynthesis
- RNA, Messenger/genetics
- Receptors, G-Protein-Coupled/biosynthesis
- Receptors, G-Protein-Coupled/genetics
- Receptors, Ghrelin
- Receptors, Neuropeptide/biosynthesis
- Receptors, Neuropeptide/genetics
- Receptors, Pituitary Hormone-Regulating Hormone/biosynthesis
- Receptors, Pituitary Hormone-Regulating Hormone/genetics
- Reverse Transcriptase Polymerase Chain Reaction/veterinary
- Sheep
- Somatotrophs/drug effects
- Somatotrophs/metabolism
- Somatotrophs/physiology
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Affiliation(s)
- Sang-Gun Roh
- Department of Food Production Science, Faculty of Agriculture, Shinshu University, Nagano-ken 5399-4598, Japan
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34
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Wong AOL, Zhou H, Jiang Y, Ko WKW. Feedback regulation of growth hormone synthesis and secretion in fish and the emerging concept of intrapituitary feedback loop. Comp Biochem Physiol A Mol Integr Physiol 2006; 144:284-305. [PMID: 16406825 DOI: 10.1016/j.cbpa.2005.11.021] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2005] [Revised: 11/21/2005] [Accepted: 11/21/2005] [Indexed: 11/21/2022]
Abstract
Growth hormone (GH) is known to play a key role in the regulation of body growth and metabolism. Similar to mammals, GH secretion in fish is under the control of hypothalamic factors. Besides, signals generated within the pituitary and/or from peripheral tissues/organs can also exert a feedback control on GH release by effects acting on both the hypothalamus and/or anterior pituitary. Among these feedback signals, the functional role of IGF is well conserved from fish to mammals. In contrast, the effects of steroids and thyroid hormones are more variable and appear to be species-specific. Recently, a novel intrapituitary feedback loop regulating GH release and GH gene expression has been identified in fish. This feedback loop has three functional components: (i) LH induction of GH release from somatotrophs, (ii) amplification of GH secretion by GH autoregulation in somatotrophs, and (iii) GH feedback inhibition of LH release from neighboring gonadotrophs. In this article, the mechanisms for feedback control of GH synthesis and secretion are reviewed and functional implications of this local feedback loop are discussed. This intrapituitary feedback loop may represent a new facet of pituitary research with potential applications in aquaculture and clinical studies.
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Affiliation(s)
- Anderson O L Wong
- Department of Zoology, University of Hong Kong, Pokfulam Road, Hong Kong, PR China.
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35
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Abstract
Ghrelin, a gastric peptide involved in growth hormone release and energy homeostasis, is the endogenous ligand of the growth hormone secretagogue receptor type 1a (GHS-R1a), a G-protein coupled receptor mainly expressed in the pituitary and hypothalamus. This receptor mediates the main ghrelin-stimulated endocrine actions and some of the nonendocrine actions. However, a number of nonendocrine actions associated with ghrelin appear to be mediated by various GHS-R1a-related receptor subtypes, which are widely distributed in the central and peripheral tissues. This review summarises data concerning the localisation, regulation and function of GHS-R1a, as well as related receptors.
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Affiliation(s)
- J P Camiña
- Laboratory of Molecular Endocrinology, Research Area, Complexo Hospitalario Universitario de Santiago (CHUS), PO Box 563, E-15780 Santiago de Compostela, Spain.
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36
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Nagaya N, Kojima M, Kangawa K. Ghrelin, a novel growth hormone-releasing peptide, in the treatment of cardiopulmonary-associated cachexia. Intern Med 2006; 45:127-34. [PMID: 16508225 DOI: 10.2169/internalmedicine.45.1402] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Ghrelin is a novel growth hormone (GH)-releasing peptide, isolated from the stomach, which has been identified as an endogenous ligand for GH secretagogue receptor. The discovery of ghrelin indicates that the release of GH from the pituitary might be regulated not only by hypothalamic GH-releasing hormone, but also by ghrelin derived from the stomach. This peptide also stimulates food intake and induces adiposity through GH-independent mechanisms. In addition, ghrelin acts directly on the central nervous system to decrease sympathetic nerve activity. Thus, ghrelin plays important roles for maintaining GH release and energy homeostasis. Repeated administration of ghrelin improves body composition, muscle wasting, functional capacity, and sympathetic augmentation in cachectic patients with heart failure or chronic obstructive pulmonary disease. These results suggest that ghrelin has anti-cachectic effects through GH-dependent and independent mechanisms. Thus, administration of ghrelin may be a new therapeutic strategy for the treatment of cardiopulmonary-associated cachexia.
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Affiliation(s)
- Noritoshi Nagaya
- Department of Regenerative Medicine and Tissue Engineering, National Cardiovascular Center Research Institute, Osaka
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37
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Lago F, Gonzalez-Juanatey JR, Casanueva FF, Gómez-Reino J, Dieguez C, Gualillo O. Ghrelin, the same peptide for different functions: player or bystander? VITAMINS AND HORMONES 2005; 71:405-32. [PMID: 16112276 DOI: 10.1016/s0083-6729(05)71014-1] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/10/2023]
Abstract
Ghrelin is a recently discovered brain-gut peptide with two main physiological actions: growth hormone secretagogue activity and food intake inducer. Although its production is prevalently gastric, ghrelin is widely expressed in several tissues, where it might therefore act as a paracrine or autocrine factor. It is becoming clear that ghrelin is much more than a simple growth hormone secretagogue. In addition to its formerly envisaged role, ghrelin has other activities including stimulation of pituitary hormones secretion, modulation of food intake and control of energy metabolism, regulation of gastric and pancreatic activity, and cardiovascular and hemodynamic activities. In addition, modulation of cartilage and bone homeostasis, sleep and behavioral influences, and modulation of the immune system, as well as effects on cell proliferation, are other relevant actions of ghrelin. Thus, the peptide appears to be an important component of an integrated multifaceted regulatory system. In this review, we summarize several aspects of ghrelin biology and attempt to inform the reader with information regarding unexpected functions of this gastric peptide.
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Affiliation(s)
- Francisca Lago
- Santiago University Clinical Hospital, Research Area, Molecular and Cellular Cardiology Laboratory 1, 15705 Santiago de Compostela, Spain
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38
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Alba M, Fintini D, Bowers CY, Parlow AF, Salvatori R. Effects of long-term treatment with growth hormone-releasing peptide-2 in the GHRH knockout mouse. Am J Physiol Endocrinol Metab 2005; 289:E762-7. [PMID: 15985453 DOI: 10.1152/ajpendo.00203.2005] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Growth hormone (GH) secretagogues (GHS) stimulate GH secretion in vivo in humans and in animals. They act on the ghrelin receptor, expressed in both the hypothalamus and the pituitary. It is unknown whether GHSs act predominantly by increasing the release of hypothalamic GH-releasing hormone (GHRH) or by acting directly on the somatotroph cells. We studied whether a potent GHS could stimulate growth in the absence of endogenous GHRH. To this end, we used GHRH knockout (GHRH-KO) mice. These animals have proportionate dwarfism due to severe GH deficiency (GHD) and pituitary hypoplasia due to reduced somatotroph cell mass. We treated male GHRH-KO mice for 6 wk (from week 1 to week 7 of age) with GH-releasing peptide-2 (GHRP-2, 10 microg s.c. twice a day). Chronic treatment with GHRP-2 failed to stimulate somatotroph cell proliferation and GH secretion and to promote longitudinal growth. GHRP-2-treated mice showed an increase in total body weight compared with placebo-treated animals, due to worsening of the body composition alterations typical of GHD animals. These data demonstrate that GHRP-2 failed to reverse the severe GHD caused by lack of GHRH.
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Affiliation(s)
- Maria Alba
- Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD, USA
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39
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Kim SW, Her SJ, Park SJ, Kim D, Park KS, Lee HK, Han BH, Kim MS, Shin CS, Kim SY. Ghrelin stimulates proliferation and differentiation and inhibits apoptosis in osteoblastic MC3T3-E1 cells. Bone 2005; 37:359-69. [PMID: 15978880 DOI: 10.1016/j.bone.2005.04.020] [Citation(s) in RCA: 144] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/06/2004] [Revised: 03/31/2005] [Accepted: 04/22/2005] [Indexed: 12/25/2022]
Abstract
Ghrelin is a 28-amino-acid peptide identified in the stomach as an endogenous ligand of the growth hormone secretagogue receptor (GHS-R) that strongly stimulates the release of growth hormone at the hypothalamus and pituitary level. Although GHS-Rs are expressed in a variety of peripheral tissues, little is known about its effect on bone independent of GH/IGF-1 axis. This study was undertaken to investigate whether ghrelin exerts a direct effect on osteoblasts. We identified mRNA and protein expression of GHS-R in primary osteoblasts as well as a number of osteoblastic cell lines, including MC3T3-E1, ROS 17/2.8, UMR-106, MG63, and SaOS2 cells. Treatment of ghrelin (10(-11) to 10(-7) M) to MC3T3-E1 cells showed dose-dependent stimulation of proliferation, which was abrogated by treatment with [d-Lys]-GHRP-6 (10(-3) M), a selective antagonist of the ghrelin receptor. Ghrelin activated ERK1/2 MAPK and pretreatment with MAPK kinase inhibitors, PD98059 attenuated the ghrelin-induced cell proliferation. Ghrelin also inhibited TNFalpha-induced apoptosis and suppressed caspase-3 activation that occurs in response to TNFalpha as well as during in vitro differentiation process. Moreover, ghrelin treatment enhanced in vitro osteoblast differentiation as evidenced by matrix mineralization, alkaline phosphatase activity, and osteoblast-specific gene expression. These results suggest that ghrelin promotes proliferation and differentiation and inhibits apoptosis of osteoblasts.
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Affiliation(s)
- Sang Wan Kim
- Department of Internal Medicine, Seoul National University College of Medicine, 28 Yungun-Dong, Chongno-Gu, Seoul 110-744, South Korea
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40
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Matarese LE, Abu-Elmagd K. Somatropin for the treatment of short bowel syndrome in adults. Expert Opin Pharmacother 2005; 6:1741-50. [PMID: 16086660 DOI: 10.1517/14656566.6.10.1741] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Somatropin (rDNA origin) injection (Zorbtive) is a highly purified preparation of human growth hormone (GH) produced from a mammalian cell line by recombinant DNA technology. It is the only human GH approved for the treatment of short bowel syndrome in patients receiving specialised nutritional support. The process of intestinal adaptation begins immediately after surgery and continues for 2-3 years. During this period, the bowel begins to increase fluid and nutrient absorption. Under the influence of tropic factors, such as GH, intestinal adaptation is enhanced. Supplying a therapeutic regimen of GH, optimised diet and glutamine supplementation for 4 weeks to patients with short bowel syndrome who are dependent on parenteral nutrition, has been shown to reduce their long-term requirements for parenteral nutrition.
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Affiliation(s)
- Laura E Matarese
- University of Pittsburgh Medical Center, Thomas E. Starzl Transplantation Institute, 3459 Fifth Avenue, MUH 7 South Pittsburgh, PA 15213, USA
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41
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Anderson LL, Jeftinija S, Scanes CG, Stromer MH, Lee JS, Jeftinija K, Glavaski-Joksimovic A. Physiology of ghrelin and related peptides. Domest Anim Endocrinol 2005; 29:111-44. [PMID: 15927771 DOI: 10.1016/j.domaniend.2005.02.033] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/25/2005] [Revised: 02/25/2005] [Accepted: 02/26/2005] [Indexed: 01/07/2023]
Abstract
Growth hormone (GH) released from pituitary under direct control of hypothalamic releasing (i.e., GHRH) and inhibiting (i.e., sst or SRIF) hormones is an anabolic hormone that regulates metabolism of proteins, fats, sugars and minerals in mammals. Cyril Bowers' discovery of GH-releasing peptide (GHRP-6) was followed by a search for synthetic peptide and nonpeptide GH-secretagogues (GHSs) that stimulate GH release, as well as a receptor(s) unique from GHRH receptor. GHRH and GHSs operate through distinct G protein-coupled receptors to release GH. Signal transduction pathways activated by GHS increase intracellular Ca2+ concentration in somatotrophs, whereas GHRH increases cAMP. Isolation and characterization of ghrelin, the natural ligand for GHS receptor, has opened a new era of understanding to physiology of anabolism, feeding behavior, and nutritional homeostasis for GH secretion and gastrointestinal motility through gut-brain interactions. Other peptide hormones (i.e., motilin, TRH, PACAP, GnRH, leptin, FMRF amide, galanin, NPY, NPW) from gut, brain and other tissues also play a role in modulating GH secretion in livestock and lower vertebrate species. Physiological processes, such as neurotransmission, and secretion of hormones or enzymes, require fusion of secretory vesicles at the cell plasma membrane and expulsion of vesicular contents. This process for GH release from porcine somatotrophs was revealed by atomic force microscopy (AFM), transmission electron microscopy (TEM) and immunohistochemical distribution of the cells in pituitary during stages of development.
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Affiliation(s)
- L L Anderson
- Department of Animal Science, College of Agriculture, Iowa State University, Ames, IA 50011-3150, USA.
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42
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Popovic V, Miljic D, Pekic S, Pesko P, Djurovic M, Doknic M, Damjanovic S, Micic D, Cvijovic G, Glodic J, Dieguez C, Casanueva FF. Low plasma ghrelin level in gastrectomized patients is accompanied by enhanced sensitivity to the ghrelin-induced growth hormone release. J Clin Endocrinol Metab 2005; 90:2187-91. [PMID: 15644398 DOI: 10.1210/jc.2004-1888] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Ghrelin is a brain-gut peptide with potent GH-releasing activities. It has been suggested that the majority of circulating ghrelin originates from the stomach, with a smaller portion from the small intestine. Gastrectomy (GASTRX) significantly reduces circulating ghrelin concentrations. The implication of decreased circulating ghrelin on the somatotropic axis post GASTRX has not been studied. Therefore, we aimed to investigate the somatotropic axis in 10 gastrectomized patients who underwent total GASTRX for various reasons at least 2 yr ago. At baseline circulating total ghrelin, GH, IGF-I, and IGF binding protein (IGFBP)-3 levels were measured. The GH stimulation test consisted of an insulin-induced hypoglycemia, ghrelin in two iv bolus doses (0.1 and 1 microg/kg), and a GHRH test. GH sensitivity was assessed by an IGF-I generation test. All the tests were performed 2 wk apart. At baseline serum ghrelin levels were reduced by 55% in GASTRX patients, compared with the control group (P < 0.05). IGF-I (P < 0.05) and IGFBP-3 (P < 0.01) levels were also significantly lower than in controls. GH response to the insulin-induced hypoglycemia test in both GASTRX and control subjects was of similar magnitude, whereas circulating plasma ghrelin levels in GASTRX patients were not modified during hypoglycemia. Both doses (0.1 and 1.0 microg/kg) of ghrelin stimulated GH release significantly more in GASTRX than control subjects, respectively (peak mean GH +/- se: 18.2 +/- 5.6 vs. 5.4 +/- 1.3 microg/liter, P < 0.03; and 58.7 +/- 7.5 vs. 35.3 +/- 1.9 microg/liter, P < 0.01). There was no difference in GHRH-induced GH response between GASTRX patients and control subjects (P > 0.05). Concomitantly, increased increments in IGF-I and IGFBP-3 to a single bolus of GH were found (P < 0.03). In conclusion, our data suggest that low circulating ghrelin levels, found in GASTRX patients, are accompanied by enhanced ghrelin sensitivity with respect to GH response. This is associated with increased GH responsiveness. GASTRX is a state of acquired chronic hypoghrelinemia that may require replacement with ghrelin, and it is tempting to speculate that this may affect the GH-IGF-IGFBP axis.
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Affiliation(s)
- Vera Popovic
- Neuroendocrine Unit, Institute of Endocrinology, Diabetes Mellitus and Metabolism, University Clinical Center, Dr Subotic 13, 11000 Belgrade, Serbia.
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43
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Ghigo E, Broglio F, Arvat E, Maccario M, Papotti M, Muccioli G. Ghrelin: more than a natural GH secretagogue and/or an orexigenic factor. Clin Endocrinol (Oxf) 2005; 62:1-17. [PMID: 15638864 DOI: 10.1111/j.1365-2265.2004.02160.x] [Citation(s) in RCA: 149] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Ghrelin, an acylated peptide produced predominantly by the stomach, has been discovered to be a natural ligand of the growth hormone secretagogue receptor type 1a (GHS-R1a). Ghrelin has recently attracted considerable interest as a new orexigenic factor. However, ghrelin exerts several other neuroendocrine, metabolic and also nonendocrine actions that are explained by the widespread distribution of ghrelin and GHS-R expression. The likely existence of GHS-R subtypes and evidence that the neuroendocrine actions, but not all the other actions, of ghrelin depend on its acylation in serine-3 revealed a system whose complexity had not been completely explored by studying synthetic GHS. Ghrelin secretion is mainly regulated by metabolic signals and, in turn, the modulatory action of ghrelin on the control of food intake and energy metabolism seems to be among its most important biological actions. However, according to a recent study, ghrelin-null mice are neither anorectics nor dwarfs and this evidence clearly depicts a remarkable difference from leptin null mice. Nevertheless, the original and fascinating story of ghrelin, as well as its potential pathophysiological implications in endocrinology and internal medicine, is not definitively cancelled by these data as GHS-R1a null aged mice show significant alterations in body composition and growth, in glucose metabolism, cardiac function and contextual memory. Besides potential clinical implications for natural or synthetic ghrelin analogues acting as agonists or antagonists, there are several open questions awaiting an answer. How many ghrelin receptor subtypes exist? Is ghrelin 'the' or just 'a' GHS-R ligand? That is, are there other natural GHS-R ligands? Is there a functional balance between acylated and unacylated ghrelin forms, potentially with different actions? Within the next few years suitable answers to these questions will probably be found, making it possible to gain a better knowledge of ghrelin's potential clinical perspectives.
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Affiliation(s)
- E Ghigo
- Division of Endocrinology and Metabolism, Department of Internal Medicine, University of Turin, Italy.
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44
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Affiliation(s)
- Felipe F Casanueva
- Department of Medicine, Faculty of Medicine, University of Santiago de Compostela, E-15780, Spain.
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45
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Fintini D, Alba M, Schally AV, Bowers CY, Parlow AF, Salvatori R. Effects of combined long-term treatment with a growth hormone-releasing hormone analogue and a growth hormone secretagogue in the growth hormone-releasing hormone knock out mouse. Neuroendocrinology 2005; 82:198-207. [PMID: 16601359 DOI: 10.1159/000092520] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/13/2005] [Accepted: 01/29/2006] [Indexed: 11/19/2022]
Abstract
GH secretagogues (GHS) are synthetic ghrelin receptor agonists that stimulate GH secretion. It is not clear whether they act predominantly by stimulating the secretion of hypothalamic growth hormone-releasing hormone (GHRH), or directly on the somatotrope cells. In addition, it is not known whether combined treatment with GHRH and GHS has synergistic effects on growth. To address these questions, we used the GH-deficient GHRH knock out (GHRHKO) mouse model, which has severe somatotrope cell hypoplasia. We treated GHRHKO mice for 5 weeks (from week 1 to week 6 of age) with the GHRH analogue JI-38 alone, or in combination with a GHS (GHRP-2), and at the end of the treatment we examined their response to an acute stimulus with GHRP-2 or GHRP-2 plus JI-38. We used placebo-treated GHRHKO mice and animals heterozygous for the GHRHKO allele as controls. Animals treated with JI-38+GHRP-2 reached higher body length and weight than animals treated with JI-38 alone. All the animals receiving JI-38 (with or without GHRP-2) showed similar correction of somatotrope cell hypoplasia. None of the GHRHKO animals showed a serum GH response to the acute stimulation with GHRP-2 alone, while both treated groups responded to the combined test with JI-38 + GHRP-2. These data demonstrate that in GHRHKO mice, GHRP-2 has a growth-stimulating effect that augments the response induced by JI-38. In addition, the presence of GHRH seems necessary for the stimulation of GH secretion by GHRP-2.
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Affiliation(s)
- Danilo Fintini
- Department of Medicine, Division of Endocrinology, and the Ilyssa Center for Molecular and Cellular Endocrinology, Johns Hopkins University School of Medicine, Baltimore, MD, USA
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Kamegai J, Tamura H, Shimizu T, Ishii S, Tatsuguchi A, Sugihara H, Oikawa S, Kineman RD. The role of pituitary ghrelin in growth hormone (GH) secretion: GH-releasing hormone-dependent regulation of pituitary ghrelin gene expression and peptide content. Endocrinology 2004; 145:3731-8. [PMID: 15087428 DOI: 10.1210/en.2003-1424] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Ghrelin is a GH-releasing peptide originally purified from the rat stomach. It has been demonstrated that ghrelin expression, within the gastroenteric system, is regulated by both the metabolic and GH milieu. Our laboratory and others have previously reported that ghrelin is also produced in the pituitary. Given that the receptor for ghrelin [GH secretagogue receptor (GHS-R)] is also expressed by the pituitary, the possibility exists that locally produced ghrelin plays an autocrine/paracrine role in regulating GH release. Because we have previously reported that GHRH infusion increases pituitary levels of ghrelin mRNA, we hypothesized that GHRH could be a key regulator of pituitary ghrelin expression. In this report, we demonstrate that 4-h GHRH infusion increased pituitary ghrelin peptide content. Interestingly, under experimental conditions in which hypothalamic GHRH expression is increased, e.g. GH deficiency due to GH gene mutation, glucocorticoid deficiency, and hypothyroidism, we observed that pituitary ghrelin expression (mRNA levels and peptide content) was also increased. Consistent with this positive correlation between GHRH and ghrelin, pituitary ghrelin expression (mRNA levels and peptide content) was found to be decreased in conditions in which hypothalamic GHRH expression is decreased, e.g. GH treatment, glucocorticoid excess, hyperthyroid state, and food deprivation. Collectively, these results suggest that pituitary ghrelin expression is GHRH dependent. We also conducted functional studies to examine whether the pituitary ghrelin/GHS-R system contributes to GH release after GHRH stimulation, by challenging pituitary cell cultures with GHRH in the presence of a GHS-R-specific inhibitor ([d-Lys-3]-GHRP-6). The GHS-R inhibitor did not affect GH release in the absence of GHRH, but significantly reduced GHRH-mediated GH release. This is the first report demonstrating that endogenous pituitary ghrelin can play a physiological role in GH release, by optimizing somatotroph responsiveness to GHRH.
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Affiliation(s)
- Jun Kamegai
- Department of Medicine, Nippon Medical School, Tokyo 113-8603, Japan.
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Broglio F, Gianotti L, Destefanis S, Fassino S, Abbate Daga G, Mondelli V, Lanfranco F, Gottero C, Gauna C, Hofland L, Van der Lely AJ, Ghigo E. The endocrine response to acute ghrelin administration is blunted in patients with anorexia nervosa, a ghrelin hypersecretory state. Clin Endocrinol (Oxf) 2004; 60:592-9. [PMID: 15104562 DOI: 10.1111/j.1365-2265.2004.02011.x] [Citation(s) in RCA: 94] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
OBJECTIVE Ghrelin, a gastric-derived natural ligand of the GH secretagogue (GHS)-receptor (GHS-R), strongly stimulates GH secretion but also possesses other neuroendocrine actions, stimulates food intake and modulates the endocrine pancreas and energy homeostasis. Ghrelin secretion is negatively modulated by food intake. Similarly, glucose and also insulin probably exert an inhibitory effect on ghrelin secretion. Fasting ghrelin levels are reduced in obesity, elevated in anorexia nervosa and restored by weight recovery. The chronic elevation of circulating ghrelin levels in anorexia suggested the hypothesis of an alteration of the sensitivity to the orexigenic action of ghrelin in this condition. The aim of this study was to define the endocrine actions of ghrelin in patients with anorexia nervosa. DESIGN We enrolled nine women with anorexia nervosa of restricter type [AN; age (mean +/- SEM) 24.2 +/- 1.8 years; body mass index (BMI) 14.7 +/- 0.4 kg/m2] and seven normal young women in their early follicular phase as control group (NW; age 30.6 +/- 3.1 years; BMI 20.3 +/- 0.5 kg/m2). MEASUREMENTS In all the subjects we studied the GH, PRL, ACTH, cortisol, insulin and glucose responses to acute ghrelin administration (1.0 microg/kg as i.v. bolus). The GH response to GHRH (1.0 microg/kg as i.v. bolus) and basal ghrelin and IGF-I levels were also evaluated in all the subjects. RESULTS Basal morning ghrelin and GH levels in AN (643.6 +/- 21.3 ng/l and 10.4 +/- 0.5 microg/l, respectively) were higher (P < 0.05) than in NW (233.5 +/- 14.2 ng/l and 0.7 +/- 0.7 microg/l, respectively). However, IGF-I levels in AN (145.3 +/- 10.9 microg/l) were lower (P < 0.05) than in NW (325.4 +/- 12.6 microg/l). The GH response to GHRH in AN was higher (P < 0.05) than that in NW, but in AN the GH response to ghrelin was lower (P < 0.05) than that in NW. In AN and NW ghrelin also induced similar increases (P < 0.05) in PRL, ACTH and cortisol levels. Ghrelin administration was followed by significant increase in glucose levels in NW (P < 0.05) but not in AN. CONCLUSIONS This study demonstrates that anorexia nervosa, a clinical condition of ghrelin hypersecretion, shows a specific reduction in the GH response to ghrelin, despite the hyper-responsiveness to GHRH administration. The impaired GH response to ghrelin in anorexia nervosa agrees with previous evidence of blunted GH response to synthetic GH secretagogues and could reflect desensitization of the GHS receptor induced by the chronic elevation of ghrelin levels in this pathological state.
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Affiliation(s)
- F Broglio
- Division of Endocrinology and Metabolism, Department of Internal Medicine, Erasmus University, Rotterdam, The Netherlands
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Chan CB, Cheng CHK. Identification and functional characterization of two alternatively spliced growth hormone secretagogue receptor transcripts from the pituitary of black seabream Acanthopagrus schlegeli. Mol Cell Endocrinol 2004; 214:81-95. [PMID: 15062547 DOI: 10.1016/j.mce.2003.11.020] [Citation(s) in RCA: 113] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/11/2003] [Accepted: 11/05/2003] [Indexed: 10/26/2022]
Abstract
Two cDNA transcripts, namely sbGHSR-1a and sbGHSR-1b, for growth hormone secretagogue receptor (GHSR), were identified from the seabream pituitary. When translated, the sbGHSR-1a encodes for a protein of 385 amino acids (aa) with seven putative transmembrane domains and the sbGHSR-1b contains 295 aa with five putative transmembrane domains. Tissue distribution studies indicated that the two receptors are mainly expressed in the central nervous system of the fish. The sbGHSR-1a transcript has the highest expression level in the pituitary. The sbGHSR-1b transcript, on the other hand, has the highest expression level in the telencephalon. Genomic Southern analysis indicated that there is a single gene for GHSR in the seabream genome. Comparison of the cDNA sequences of sbGHSR1a and sbGHSR1b with the seabream genomic sequence indicated that the presence of the two receptor transcripts is a result of alternative splicing of the single GHSR gene. The two receptor cDNAs were expressed in cultured eukaryotic cells for functional analyses. A variety of structurally diverse growth hormone secretogogues (GHS), including the peptide GHS (GHRP-6 and ghrelin), the benzolactam GHS (L692,585) and the spiropiperidine GHS (L163,255), were able to trigger an elevation of intracellular Ca(2+) ion concentration in HEK293 cells expressing sbGHSR-1a, but not in cells expressing sbGHSR-1b. Microphysiometry revealed that an increase in extracellular acidification rate (EAR) could be detected in CHO cells expressing the sbGHSR-1a receptor when stimulated with GHRP-6. On the contrary, CHO cells expressing the sbGHSR-1b receptor registered no detectable EAR changes. However, when sbGHSR-1b was co-expressed with sbGHSR-1a in HEK293 cells, the signal transduction capacity of sbGHSR-1a was attenuated. This is the first report on the identification of a GHSR-1b transcript from species other than mammals and the demonstration that receptor interaction might provide a possible explanation for the existence and biological significance of the sbGHSR-1b transcript.
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Affiliation(s)
- Chi-Bun Chan
- Department of Biochemistry, The Chinese University of Hong Kong, Shatin, NT, Hong Kong, China
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Bresciani E, Nass R, Torsello A, Gaylinn B, Avallone R, Locatelli V, Thorner MO, Müller EE. Hexarelin modulates the expression of growth hormone secretagogue receptor type 1a mRNA at hypothalamic and pituitary sites. Neuroendocrinology 2004; 80:52-9. [PMID: 15361691 DOI: 10.1159/000080793] [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: 01/05/2004] [Accepted: 06/17/2004] [Indexed: 11/19/2022]
Abstract
Ghrelin and the synthetic growth hormone secretagogues (GHSs) activate a G-protein-coupled receptor (GHS-R) originally cloned from the pituitary, but which is also expressed in the hypothalamus, in other areas of the brain and in numerous peripheral tissues. Several studies have shown that growth hormone (GH)-releasing hormone (GHRH) is necessary for GHSs to exert maximal GH release in vivo. The exact mechanism of this synergism is not clear. Previous data suggest that GHSs can affect pituitary GHS-R mRNA expression; however, it is unknown whether this effect is age dependent and whether hypothalamic GHS-Rs are also affected. In this study, we tested whether (a) the synthetic GHS hexarelin regulates mRNA expression of its own receptor at the pituitary and/or hypothalamus and whether this effect is age dependent, and (b) whether short-term treatment with GHRH or, conversely, passive immunization against GHRH affects pituitary GHS-R1a mRNA expression in infant (10 days old) and young adult rats. GHS-R1a mRNA expression was measured with competitive reverse transcriptase-polymerase chain reaction. Hexarelin treatment significantly increased pituitary and hypothalamic GHS-R1a mRNA levels in normal infant rats, but not in normal young adult rats. In addition, hexarelin administration also stimulated pituitary GHS-R1a mRNA in infant as well as in young adult rats passively immunized against GHRH. GHRH treatment significantly enhanced pituitary GHS-R1a mRNA expression in GHRH-deprived young adult rats, though it did not affect the basal levels of GHS-R1a mRNA in normal infant and adult rats. These data further support the hypothesis that GHRH can affect GHS-R1a expression and that hexarelin upregulates the expression of its own receptor at the pituitary as well as the hypothalamus in an age-dependent fashion.
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Affiliation(s)
- Elena Bresciani
- Department of Experimental and Environmental Medicine and Biotechnology, University of Milano-Bicocca, Monza, Italy.
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Malagón MM, Luque RM, Ruiz-Guerrero E, Rodríguez-Pacheco F, García-Navarro S, Casanueva FF, Gracia-Navarro F, Castaño JP. Intracellular signaling mechanisms mediating ghrelin-stimulated growth hormone release in somatotropes. Endocrinology 2003; 144:5372-80. [PMID: 12960033 DOI: 10.1210/en.2003-0723] [Citation(s) in RCA: 103] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Ghrelin is a newly discovered peptide that binds the receptor for GH secretagogues (GHS-R). The presence of both ghrelin and GHS-Rs in the hypothalamic-pituitary system, together with the ability of ghrelin to increase GH release, suggests a hypophysiotropic role for this peptide. To ascertain the intracellular mechanisms mediating the action of ghrelin in somatotropes, we evaluated ghrelin-induced GH release from pig pituitary cells both under basal conditions and after specific blockade of key steps of cAMP-, inositol phosphate-, and Ca2+-dependent signaling routes. Ghrelin stimulated GH release at concentrations ranging from 10-10 to 10-6 m. Its effects were comparable with those exerted by GHRH or the GHS L-163,255. Combined treatment with ghrelin and GHRH or L-163,255 did not cause further increases in GH release, whereas somatostatin abolished the effect of ghrelin. Blockade of phospholipase C or protein kinase C inhibited ghrelin-induced GH secretion, suggesting a requisite role for this route in ghrelin action. Unexpectedly, inhibition of either adenylate cyclase or protein kinase A also suppressed ghrelin-induced GH release. In addition, ghrelin stimulated cAMP production and also had an additive effect with GHRH on cAMP accumulation. Ghrelin also increased free intracellular Ca2+ levels in somatotropes. Moreover, ghrelin-induced GH release was entirely dependent on extracellular Ca2+ influx through L-type voltage-sensitive channels. These results indicate that ghrelin exerts a direct stimulatory action on porcine GH release that is not additive with that of GHRH and requires the contribution of a multiple, complex set of interdependent intracellular signaling pathways.
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Affiliation(s)
- María M Malagón
- Department of Cell Biology, University of Córdoba, Córdoba, Spain.
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