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Bergan-Roller HE, Sheridan MA. The growth hormone signaling system: Insights into coordinating the anabolic and catabolic actions of growth hormone. Gen Comp Endocrinol 2018; 258:119-133. [PMID: 28760716 DOI: 10.1016/j.ygcen.2017.07.028] [Citation(s) in RCA: 90] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/18/2017] [Revised: 07/19/2017] [Accepted: 07/27/2017] [Indexed: 12/16/2022]
Abstract
Although growth hormone (GH) is a multifunctional factor that coordinates various aspects of feeding, reproduction, osmoregulation, and immune system function, perhaps two of its most studied actions are the regulation of growth and metabolism, particularly lipid metabolism. In this review, we describe the major growth-promoting and lipid metabolic actions of GH and then discuss how the GH system regulates these actions. Numerous intrinsic and extrinsic factors provide information about the metabolic status of the organism and influence the production of release of GH. The actions of GH are mediated by GH receptors (GHR), which are widely distributed among tissues. Teleosts possess multiple forms of GHRs that arose through the evolution of this group. Modulation of tissue responsiveness to GH is regulated by molecular and functional expression of GHRs, and in teleosts GHR subtypes, by various factors that reflect the metabolic and growth status of the organism, including nutritional state. The action of GH is propagated by the linkage of GHRs to several cellular effector systems, including JAK-STAT, ERK, PI3K-Akt, and PKC. The differential activation of these pathways, which is governed by nutrient status, underlies GH stimulation of growth or GH stimulation of lipolysis. Taken together, the multi-functional actions of GH are determined by the distribution and abundance of GHRs (and GHR subtypes in teleosts) as well as by the GHR-effector system linkages.
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Affiliation(s)
| | - Mark A Sheridan
- Department of Biological Sciences, Texas Tech University, Lubbock, TX 79409 USA.
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2
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Pardeshi R, Bolshette N, Gadhave K, Ahire A, Ahmed S, Cassano T, Gupta VB, Lahkar M. Insulin signaling: An opportunistic target to minify the risk of Alzheimer's disease. Psychoneuroendocrinology 2017. [PMID: 28624654 DOI: 10.1016/j.psyneuen.2017.05.004] [Citation(s) in RCA: 47] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Alzheimer's disease (AD) is progressive neurodegenerative disorder characterized by accumulation of senile plaques, neurofibrillary tangles (NFT) and neurodegeneration. The diabetes mellitus (DM) is one of the risk factors for AD pathogenesis by impairment in insulin signaling and glucose metabolism in central as well as peripheral system. Insulin resistance, impaired glucose and lipid metabolism are leading to the Aβ (Aβ) aggregation, Tau phosphorylation, mitochondrial dysfunction, oxidative stress, protein misfolding, memory impairment and also mark over Aβ transport through central to peripheral and vice versa. Several pathways, like enzymatic degradation of Aβ, forkhead box protein O1 (FOXO) signaling, insulin signaling shared common pathological mechanism for both AD and DM. Recent evidence showed that hyperinsulinemia and hyperglycemia affect the onset and progression of AD differently. Some researchers have suggested that hyperglycemia influences vascular tone, while hyperinsulinemia may underlie mitochondrial deficit. The objective of this review is to determine whether existing evidence supports the concept that impairment in insulin signaling and glucose metabolism play an important role in pathogenesis of AD. In the first part of this review, we tried to explain the interconnecting link between AD and DM, whereas the second part includes more information on insulin resistance and its involvement in AD pathogenesis. In the final part of this review, we have focused more toward the AD treatment by targeting insulin signaling like anti-diabetic, antioxidant, nutraceuticals and dietary supplements. To date, more researches should be done in this field in order to explore the pathways in insulin signaling, which might ameliorate the treatment options and reduce the risk of AD due to DM.
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Affiliation(s)
- Rohit Pardeshi
- Department of Biotechnology, National Institute of Pharmaceutical Education and Research (NIPER), Gauhati Medical College, Guwahati 781032, Assam, India
| | - Nityanand Bolshette
- Institutional Level Biotech hub (IBT hub), Department of Biotechnology, National Institute of Pharmaceutical Education and Research (NIPER), Gauhati Medical College, Guwahati 781032, Assam, India
| | - Kundlik Gadhave
- Department of Pharmacology and Toxicology, National Institute of Pharmaceutical Education and Research (NIPER), Gauhati Medical College, Guwahati 781032, Assam, India
| | - Ashutosh Ahire
- Department of Pharmacology and Toxicology, National Institute of Pharmaceutical Education and Research (NIPER), Gauhati Medical College, Guwahati 781032, Assam, India
| | - Sahabuddin Ahmed
- Department of Pharmacology and Toxicology, National Institute of Pharmaceutical Education and Research (NIPER), Gauhati Medical College, Guwahati 781032, Assam, India
| | - Tommaso Cassano
- Department of Clinical and Experimental Medicine, University of Foggia, Via Luigi Pinto, c/o Ospedali Riuniti, 71122 Foggia, Italy
| | - Veer Bala Gupta
- Centre of Excellence for Alzheimer's Disease Research & Care, School of Medical Sciences, Edith-Cowan University, Joondalup, WA 6027, Australia
| | - Mangala Lahkar
- Department of Biotechnology, National Institute of Pharmaceutical Education and Research (NIPER), Gauhati Medical College, Guwahati 781032, Assam, India; Institutional Level Biotech hub (IBT hub), Department of Biotechnology, National Institute of Pharmaceutical Education and Research (NIPER), Gauhati Medical College, Guwahati 781032, Assam, India; Department of Pharmacology and Toxicology, National Institute of Pharmaceutical Education and Research (NIPER), Gauhati Medical College, Guwahati 781032, Assam, India.
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3
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Sgrò P, Sansone M, Parisi A, Sartorio A, Sansone A, Romanelli F, Lenzi A, Di Luigi L. Supra-physiological rhGH administration induces gender-related differences in the hypothalamus-pituitary-thyroid (HPT) axis in healthy individuals. J Endocrinol Invest 2016; 39:1383-1390. [PMID: 27230547 DOI: 10.1007/s40618-016-0489-6] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/26/2015] [Accepted: 05/14/2016] [Indexed: 10/21/2022]
Abstract
PURPOSE The use of recombinant human growth hormone (rhGH) is a common habit among athletes. While the effects of rhGH administration have been described with contrasting results in males, no data exist in females to date. The aim of the present study was to evaluate the effects of rhGH administration on TSH, FT4 and FT3 levels and the time requested to return to baseline values after treatment withdrawal. METHODS Twenty-one healthy trained male and female athletes were treated with 0.03 mg rhGH/kg body mass 6 days/week for 3 weeks. We collected blood samples immediately before the first daily rhGH administration, at 3, 4, 8, 15 and 21 days of treatment and at 3 and 9 days after rhGH withdrawal. RESULTS In males, rhGH administration induced a significant (p < 0.01) early and stable TSH decrease and IGF-I increase, and a delayed FT4 reduction without FT3 modification, suggesting a central regulatory mechanism. In females, rhGH administration induced a significant (p < 0.01) early and transient TSH decrease and IGF-I increase, and a transient reduction in FT4 without any changes in FT3 concentrations. rhGH withdrawal was associated with a prompt normalization of TSH and FT4 levels in males, while in females the effects of rhGH treatment had already disappeared during the last period of treatment. CONCLUSION We suggest that rhGH inhibits TSH at central level both in males and females. The pattern of normalization was different in the two genders probably due to gonadal steroids modulation on GH-IGF-I axis.
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Affiliation(s)
- P Sgrò
- Unit of Endocrinology, Department of Motor, Human and Health Sciences, University of Rome "Foro Italico", Piazza Lauro de Bosis, 15, 00135, Rome, Italy.
| | - M Sansone
- Department of Experimental Medicine, "Sapienza" University of Rome, Viale Regina Elena 324, 00161, Rome, Italy
| | - A Parisi
- Unit of Sports Medicine, Department of Motor, Human and Health Sciences, University of Rome "Foro Italico" , Piazza Lauro de Bosis, 15, 00135, Rome, Italy
| | - A Sartorio
- Experimental Laboratory for Auxo-endocrinological Research, Istituto Auxologico Italiano, Via Ariosto, 13, 20145, Milan, Italy
| | - A Sansone
- Department of Experimental Medicine, "Sapienza" University of Rome, Viale Regina Elena 324, 00161, Rome, Italy
| | - F Romanelli
- Department of Experimental Medicine, "Sapienza" University of Rome, Viale Regina Elena 324, 00161, Rome, Italy
| | - A Lenzi
- Department of Experimental Medicine, "Sapienza" University of Rome, Viale Regina Elena 324, 00161, Rome, Italy
| | - L Di Luigi
- Unit of Endocrinology, Department of Motor, Human and Health Sciences, University of Rome "Foro Italico", Piazza Lauro de Bosis, 15, 00135, Rome, Italy
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Sundström K, Cedervall T, Ohlsson C, Camacho-Hübner C, Sävendahl L. Combined treatment with GH and IGF-I: additive effect on cortical bone mass but not on linear bone growth in female rats. Endocrinology 2014; 155:4798-807. [PMID: 25243853 DOI: 10.1210/en.2014-1160] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The growth-promoting effect of combined therapy with GH and IGF-I in normal rats is not known. We therefore investigated the efficacy of treatment with recombinant human (rh)GH and/or rhIGF-I on longitudinal bone growth and bone mass in intact, prepubertal, female Sprague-Dawley rats. rhGH was injected twice daily sc (5 mg/kg·d) and rhIGF-I continuously infused sc (2.2 or 4.4 mg/kg·d) for 28 days. Longitudinal bone growth was monitored by weekly x-rays of tibiae and nose-anus length measurements, and tibial growth plate histomorphology was analyzed. Bone mass was evaluated by peripheral quantitative computed tomography. In addition, serum levels of IGF-I, rat GH, acid labile subunit, IGF binding protein-3, 150-kDa ternary complex formation, and markers of bone formation and degradation were measured. Monotherapy with rhGH was more effective than rhIGF-I (4.4 mg/kg·d) to increase tibia and nose-anus length, whereas combined therapy did not further increase tibia, or nose-anus, lengths or growth plate height. In contrast, combined rhGH and rhIGF-I (4.4 mg/kg·d) therapy had an additive stimulatory effect on cortical bone mass vs rhGH alone. Combined treatment with rhGH and rhIGF-I resulted in markedly higher serum IGF-I concentrations vs rhGH alone but did not compromise the endogenous secretion of GH. We conclude that rhIGF-I treatment augments cortical bone mass but does not further improve bone growth in rhGH-treated young, intact, female rats.
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Affiliation(s)
- Katja Sundström
- Pediatric Endocrinology Unit (K.S., T.C., C.C.-H., L.S.), Department of Women's and Children's Health, Karolinska Institutet, SE-17176 Stockholm, Sweden; and Centre for Bone and Arthritis Research (C.O.), Institute of Medicine, Sahlgrenska Academy, University of Gothenburg, SE-41345 Gothenburg, Sweden
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Ma DM, Han LQ, Bai JJ, Li SJ, Fan JJ, Yu LY, Quan YC. A 66-bp deletion ingrowth hormone releasing hormonegene 5′-flanking region with largemouth bass recessive embryonic lethal. Anim Genet 2014; 45:421-6. [DOI: 10.1111/age.12143] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/03/2014] [Indexed: 11/30/2022]
Affiliation(s)
- D M Ma
- Key Laboratory of Tropical & Subtropical Fishery Resource Application & Cultivation, Ministry of Agriculture of the People's Republic of China, Pearl River Fisheries Research Institute, Chinese Academy of Fishery Sciences, Guangzhou, 510380, China
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Gahete MD, Córdoba-Chacón J, Lin Q, Brüning JC, Kahn CR, Castaño JP, Christian H, Luque RM, Kineman RD. Insulin and IGF-I inhibit GH synthesis and release in vitro and in vivo by separate mechanisms. Endocrinology 2013; 154:2410-20. [PMID: 23671263 PMCID: PMC3689283 DOI: 10.1210/en.2013-1261] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
IGF-I is considered a primary inhibitor of GH secretion. Insulin may also play an important role in regulating GH levels because insulin, like IGF-I, can suppress GH synthesis and release in primary pituitary cell cultures and insulin is negatively correlated with GH levels in vivo. However, understanding the relative contribution insulin and IGF-I exert on controlling GH secretion has been hampered by the fact that circulating insulin and IGF-I are regulated in parallel and insulin (INSR) and IGF-I (IGFIR) receptors are structurally/functionally related and ubiquitously expressed. To evaluate the separate roles of insulin and IGF-I in directly regulating GH secretion, we used the Cre/loxP system to knock down the INSR and IGFIR in primary mouse pituitary cell cultures and found insulin-mediated suppression of GH is independent of the IGFIR. In addition, pharmacological blockade of intracellular signals in both mouse and baboon cultures revealed insulin requires different pathways from IGF-I to exert a maximal inhibitory effect on GH expression/release. In vivo, somatotrope-specific knockout of INSR (SIRKO) or IGFIR (SIGFRKO) increased GH levels. However, comparison of the pattern of GH release, GH expression, somatotrope morphometry, and pituitary explant sensitivity to acute GHRH challenge in lean SIRKO and SIGFRKO mice strongly suggests the primary role of insulin in vivo is to suppress GH release, whereas IGF-I serves to regulate GH synthesis. Finally, SIRKO and/or SIGFRKO could not prevent high-fat, diet-induced suppression of pituitary GH expression, indicating other factors/tissues are involved in the decline of GH observed with weight gain.
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Affiliation(s)
- Manuel D Gahete
- Research and Development Division, Department of Medicine, University of Illinois at Chicago, Chicago, IL 60612, USA
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7
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Puche JE, Castilla-Cortázar I. Human conditions of insulin-like growth factor-I (IGF-I) deficiency. J Transl Med 2012; 10:224. [PMID: 23148873 PMCID: PMC3543345 DOI: 10.1186/1479-5876-10-224] [Citation(s) in RCA: 164] [Impact Index Per Article: 13.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2012] [Accepted: 11/07/2012] [Indexed: 12/13/2022] Open
Abstract
Insulin-like growth factor I (IGF-I) is a polypeptide hormone produced mainly by the liver in response to the endocrine GH stimulus, but it is also secreted by multiple tissues for autocrine/paracrine purposes. IGF-I is partly responsible for systemic GH activities although it possesses a wide number of own properties (anabolic, antioxidant, anti-inflammatory and cytoprotective actions). IGF-I is a closely regulated hormone. Consequently, its logical therapeutical applications seems to be limited to restore physiological circulating levels in order to recover the clinical consequences of IGF-I deficiency, conditions where, despite continuous discrepancies, IGF-I treatment has never been related to oncogenesis. Currently the best characterized conditions of IGF-I deficiency are Laron Syndrome, in children; liver cirrhosis, in adults; aging including age-related-cardiovascular and neurological diseases; and more recently, intrauterine growth restriction. The aim of this review is to summarize the increasing list of roles of IGF-I, both in physiological and pathological conditions, underlying that its potential therapeutical options seem to be limited to those proven states of local or systemic IGF-I deficiency as a replacement treatment, rather than increasing its level upper the normal range.
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Affiliation(s)
- Juan E Puche
- Applied Molecular Medicine Institute (IMMA), School of Medicine, Department of Medical Physiology, Universidad CEU San Pablo, Madrid, Spain
| | - Inma Castilla-Cortázar
- Applied Molecular Medicine Institute (IMMA), School of Medicine, Department of Medical Physiology, Universidad CEU San Pablo, Madrid, Spain
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9
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Kim E, Seo S, Chung H, Park S. Role of Glucocorticoids in Fasting-induced Changes in Hypothalamic and Pituitary Components of the Growth Hormone (GH)-axis. THE KOREAN JOURNAL OF PHYSIOLOGY & PHARMACOLOGY : OFFICIAL JOURNAL OF THE KOREAN PHYSIOLOGICAL SOCIETY AND THE KOREAN SOCIETY OF PHARMACOLOGY 2008; 12:217-23. [PMID: 19967059 DOI: 10.4196/kjpp.2008.12.5.217] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
To directly test if elevated glucocorticoids are required for fasting-induced regulation of growth hormone (GH)-releasing hormone (GHRH), GHRH receptors (GHRH-R) and ghrelin receptors (GHS-R) expression, male rats were bilaterally adrenalectomized or sham operated. After 7 days, animals were fed ad libitum or fasted for 48 h. Bilateral adrenalectomy increased hypothalamic GHRH to 146% and decreased neuropeptide Y (NPY) mRNA to 54% of SHAM controls. Pituitary GHRH-R and GHS-R mRNA levels were decreased by adrenalectomy to 30% and 80% of sham-operated controls. In shamoperated rats, fasting suppressed hypothalamic GHRH (49%) and stimulated NPY (166%) mRNA levels, while fasting increased pituitary GHRH-R (391%) and GHS-R (218%) mRNA levels. However, in adrenalectomized rats, fasting failed to alter pituitary GHRH-R mRNA levels, while the fasting-induced suppression of GHRH and elevation of NPY and GHS-R mRNA levels remained intact. In fasted adrenalectomized rats, corticosterone replacement increased GHRH-R mRNA levels and intensified the fasting-induced decrease in GHRH, but did not alter NPY or GHS-R response. These data suggest that elevated glucocorticoids mediate the effects of fasting on hypothalamic GHRH and pituitary GHRH-R expression, while glucocorticoids are likely not the major determinant in fasting-induced increases in hypothalamic NPY and pituitary GHS-R expression.
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Affiliation(s)
- Eunhee Kim
- Department of Pharmacology and Medical Research Center for Bioreaction to ROS and Biomedical Science Institute, Kyunghee University School of Medicine, Seoul 130-701, Korea
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Burgos-Ramos E, Hervás-Aguilar A, Aguado-Llera D, Puebla-Jiménez L, Hernández-Pinto AM, Barrios V, Arilla-Ferreiro E. Somatostatin and Alzheimer's disease. Mol Cell Endocrinol 2008; 286:104-11. [PMID: 18359553 DOI: 10.1016/j.mce.2008.01.014] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/11/2007] [Revised: 01/23/2008] [Accepted: 01/24/2008] [Indexed: 11/22/2022]
Abstract
Alzheimer's disease (AD) is characterized by the cerebral deposition of senile plaques that are mainly composed of a set of peptides referred to as amyloid beta-peptides (Abeta). Among the numerous neuropeptides produced in intrinsic cortical and hippocampal neurons, somatostatin (SRIF) has been found to be the most consistently reduced in the brain and cerebrospinal fluid of AD patients. SRIF receptors (SSTR), which mediate the neuromodulatory signals of SRIF, are also markedly depleted in the AD brain, there being subtype-selective alterations in cortical areas. In the rat temporal cortex, we have shown that intracerebroventricular infusion of Abeta25-35 results in a decrease in SRIF-like immunoreactivity and in SRIF receptor subtype 2 (SSTR2) mRNA and protein levels, in correlation with a decrease in SSTR functionality. Insulin-like growth factor-I prevents the reduction in these parameters induced by Abeta25-35. Abeta has recently been demonstrated to be degraded primarily by a neutral endopeptidase, neprilysin, in the brain. SRIF regulates brain Abeta levels via modulation of neprilysin activity. Because SRIF expression in the brain declines upon aging in various mammals, including rodents, apes and humans, the aging-dependent reduction of SRIF has been hypothesized to trigger accumulation of Abeta in the brain by suppressing neprilysin action. Here we present an overview of recent advances on the role of SRIF in AD and its relationship with Abeta peptides.
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Affiliation(s)
- E Burgos-Ramos
- Unidad de Neurobioquímica, Departamento de Bioquímica y Biología Molecular, Facultad de Medicina, Universidad de Alcalá, Madrid, Spain
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Luque RM, Park S, Kineman RD. Role of endogenous somatostatin in regulating GH output under basal conditions and in response to metabolic extremes. Mol Cell Endocrinol 2008; 286:155-68. [PMID: 18258353 DOI: 10.1016/j.mce.2007.12.005] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/18/2007] [Revised: 11/28/2007] [Accepted: 12/05/2007] [Indexed: 01/26/2023]
Abstract
Somatostatin (SST) was first described over 30 years ago as a hypothalamic neuropeptide which inhibits GH release. Since that time a large body of literature has accumulated describing how endogenous SST mediates its effects on GH-axis function under normal conditions and in response to metabolic extremes. This review serves to summarize the key findings in this field with a focus on recent progress, much of which has been made possible by the availability of genetically engineered mouse models and SST receptor-specific agonists.
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Affiliation(s)
- Raul M Luque
- Department of Medicine, University of Illinois at Chicago, Chicago, IL 60612, USA
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12
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Luque RM, Kineman RD. Gender-dependent role of endogenous somatostatin in regulating growth hormone-axis function in mice. Endocrinology 2007; 148:5998-6006. [PMID: 17761762 DOI: 10.1210/en.2007-0946] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
It has been previously reported that male and female somatostatin (SST) knockout mice (Sst-/-) release more GH, compared with Sst+/+ mice, due to enhanced GH-secretory vesicle release. Endogenous SST may also regulate GH secretion by directly inhibiting GHRH-stimulated GH gene expression and/or by modulating hypothalamic GHRH input. To begin to explore these possibilities and to learn more about the gender-dependent role of SST in modulating GH-axis function, hypothalamic, pituitary, and liver components of the GH-axis were compared in male and female Sst+/+ and Sst-/- mice. Pituitary mRNA levels for GH and receptors for GHRH and ghrelin were increased in female Sst-/- mice, compared with Sst+/+ controls, and these changes were reflected by an increase in circulating GH and IGF-I. Elevated levels of IGF-I in female Sst-/- mice were associated with elevated hepatic mRNA levels for IGF-I, as well as for GH and prolactin receptors. Consistent with the role of GH/IGF-I in negative feedback regulation of hypothalamic function, GHRH mRNA levels were reduced in female Sst-/- mice, whereas cortistatin (CST) mRNA levels were unaltered. In contrast to the widespread impact of SST loss on GH-axis function in females, only circulating GH, hypothalamic CST, and hepatic prolactin receptor expression were up-regulated in Sst-/- male mice, compared with Sst+/+ controls. These results confirm and extend the sexually dimorphic role of SST on GH-axis regulation, and suggest that CST, a neuropeptide that acts through SST receptors to inhibit GH secretion, may serve a compensatory role in maintaining GH-axis function in Sst-/- male mice.
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MESH Headings
- Animals
- Blotting, Northern
- Cells, Cultured
- Enzyme-Linked Immunosorbent Assay
- Female
- Gene Deletion
- Growth Hormone/blood
- Growth Hormone/genetics
- Growth Hormone/metabolism
- Insulin-Like Growth Factor I/genetics
- Insulin-Like Growth Factor I/metabolism
- Liver/metabolism
- Male
- Mice
- Mice, Inbred C57BL
- Mice, Knockout
- Pituitary Gland/cytology
- Pituitary Gland/metabolism
- Radioimmunoassay
- Receptors, Ghrelin/blood
- Receptors, Ghrelin/genetics
- Receptors, Ghrelin/metabolism
- Receptors, Pituitary Hormone-Regulating Hormone/blood
- Receptors, Pituitary Hormone-Regulating Hormone/genetics
- Receptors, Pituitary Hormone-Regulating Hormone/metabolism
- Reverse Transcriptase Polymerase Chain Reaction
- Sex Factors
- Somatostatin/genetics
- Somatostatin/physiology
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Affiliation(s)
- Raul M Luque
- Jesse Brown Veterans Affairs Medical Center, Research and Development Division, M.P 151, West Side, 820 South Damen Avenue, Chicago, IL 60612, USA
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Luque RM, Park S, Kineman RD. Severity of the catabolic condition differentially modulates hypothalamic expression of growth hormone-releasing hormone in the fasted mouse: potential role of neuropeptide Y and corticotropin-releasing hormone. Endocrinology 2007; 148:300-9. [PMID: 17038558 DOI: 10.1210/en.2006-0592] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
To determine whether the severity of the catabolic condition differentially regulates the GH axis, male mice were either fed ad libitum or fasted for 12, 24, and 48 h. Hypothalami, pituitaries, and stomachs were collected for assessment of mRNA levels by quantitative real-time RT-PCR, and blood collected for measurement of plasma hormone and metabolite levels by commercial assay kits. Overnight (12 h) fasting resulted in a significant suppression of circulating glucose, insulin, IGF-I, and leptin levels and an increase in corticosterone, free fatty acids, and n-octanoyl ghrelin levels, and these directional changes were maintained at the 24- and 48-h time points. Fasting (24 h) also increased circulating GH levels, which was associated with an increase in pituitary mRNA levels for GHRH receptor and ghrelin receptor and a decrease in mRNA levels for somatostatin (SST) receptor (SSTR) subtypes, SSTR2, SSTR3, and SSTR5, where the changes in ghrelin receptor and SSTR expression persisted after 48 h fasting. Hypothalamic SST mRNA levels were not altered by fasting, whereas there was a transient rise in stomach SST mRNA levels 24 h after food withdrawal. In contrast, there was a biphasic effect of fasting on GHRH expression. GHRH mRNA levels were significantly elevated at 12 and 24 h but fell to approximately 50% of fed controls 48 h after food withdrawal. A sequential rise in hypothalamic neuropeptide Y (NPY) and CRH mRNA levels preceded the fall in GHRH expression, where fasting-induced changes in CRH and GHRH mRNA levels were not observed in 48-h-fasted NPY knockout mice. These observations, in light of previous reports showing both NPY and CRH can inhibit GHRH expression and GH release, suggest that these neuronal systems may work in concert to control the ultimate impact of fasting on GH axis function.
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Affiliation(s)
- Raul M Luque
- Department of Medicine, University of Illinois, Chicago, USA
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14
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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: 79] [Impact Index Per Article: 4.4] [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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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: 1.4] [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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16
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Nelson LE, Sheridan MA. Regulation of somatostatins and their receptors in fish. Gen Comp Endocrinol 2005; 142:117-33. [PMID: 15862556 DOI: 10.1016/j.ygcen.2004.12.002] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/30/2004] [Revised: 12/02/2004] [Accepted: 12/13/2004] [Indexed: 01/12/2023]
Abstract
The multifunctional nature of the somatostatin (SS) family of peptides results from a multifaceted signaling system consisting of many forms of SS peptides that bind to a variety of receptor (SSTR) subtypes. Research in fish has contributed important information about the components, function, evolution, and regulation of this system. Somatostatins or mRNAs encoding SSs have been isolated from over 20 species of fish. Peptides and deduced peptides differ in their amino acid chain length and/or composition, and most species of fish possess more than one form of SS. The structural heterogeneity of SSs results from differential processing of the hormone precursor, preprosomatostatin (PPSS), and from the existence of multiple genes that give rise to multiple PPSSs. The PPSS genes appear to have arisen through a series of gene duplication events over the course of vertebrate evolution. The numerous PPSSs of fish are differentially expressed, both in terms of the distribution among tissues and in terms of the relative abundance within a tissue. Accumulated evidence suggests that nutritional state, season/stage of sexual maturation, and many hormones [insulin (INS), glucagon, growth hormone (GH), insulin-like growth factor-I (IGF-I), and 17beta-estradiol (E2)] regulate the synthesis and release of particular SSs. Fish and mammals possess multiple SSTRs; four different SSTRs have been described in fish and several of these occur as isoforms. SSTRs are also wide spread and are differentially expressed, both in terms of distribution of tissues as well as in terms of relative abundance within tissues. The pattern of distribution of SSTRs may underlie tissue-specific responses of SSs. The synthesis of SSTR mRNA and SS-binding capacity are regulated by nutritional state and numerous hormones (INS, GH, IGF-I, and E2). Accumulated evidence suggests the possibility of both tissue- and subtype-specific mechanisms of regulation. In many instances, there appears to be coordinate regulation of PPSS and of SSTR; such regulation may prove important for many processes, including nutrient homeostasis and growth control.
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Affiliation(s)
- Laura E Nelson
- Department of Biological Sciences, North Dakota State University, Fargo, ND 58105, USA
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17
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Aguado-Llera D, Arilla-Ferreiro E, Campos-Barros A, Puebla-Jiménez L, Barrios V. Protective effects of insulin-like growth factor-I on the somatostatinergic system in the temporal cortex of beta-amyloid-treated rats. J Neurochem 2005; 92:607-15. [PMID: 15659230 DOI: 10.1111/j.1471-4159.2004.02889.x] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Insulin-like growth factor-I (IGF-I) has protective effects against beta-amyloid (Abeta)-induced neuronal cell death. Because alterations of the somatostatinergic system have been described in Alzheimer's disease, we investigated the effects of the Abeta peptide and the possible protective role of IGF-I on the somatostatinergic system of the rat temporal cortex and on cell death and phosphorylated (p)-Akt levels in this area. Abeta25-35 was administered intracerebroventricularly to male rats via an osmotic minipump over 14 days (300 pmol/day). Another group received a subcutaneous IGF-I infusion (50 microg/kg/day), concomitant with Abeta25-35 administration, whereas a third group received IGF-I alone. Abeta25-35 significantly decreased the somatostatin (SRIF)-like immunoreactive content and the SRIF receptor density, as a result of a decrease in the levels of the SRIF receptor subtype 2. The inhibitory effect of SRIF on adenylyl cyclase activity was significantly lower after Abeta25-35 infusion, whereas the levels of the inhibitory G protein subunit Gialpha1, Gialpha2 or Gialpha3 were unaltered. Cell death was increased and p-Akt levels decreased in Abeta25-35-treated animals. IGF-I administration increased immunoreactive IGF-I levels in the temporal cortex and restored all parameters affected by Abeta25-35 to baseline values. These findings suggest that IGF-I prevents the deleterious effect of Abeta25-35 on the somatostatinergic system.
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Affiliation(s)
- D Aguado-Llera
- Research Laboratory, Universidad Autónoma, Hospital Infantil Universitario Niño Jesús, Avda. Menéndez Pelayo 65, E-28009 Madrid, Spain
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18
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Veyrat-Durebex C, Gaudreau P, Boghossian S, Alliot J. Effects of peripheral and central administration of GHRH on feeding in aging LOU rats. Peptides 2001; 22:2119-26. [PMID: 11786199 DOI: 10.1016/s0196-9781(01)00560-5] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
In aging LOU rats, a decreased protein intake is restored by GH administration. To study the contribution of GHRH to macronutrient selection, hGHRH NH(2) was administered sc. (1 mg/kg B.W./day/14 days) or icv. (4 and 40 pmol/rat) to 11-, 19-, 24- and 28-month-old rats. Sc. administration induced a decreased food and lipid intakes from 24 months of age and a transient stimulation of protein intake in 19-month-old and older low protein eaters (<10% protein/total intake). Icv. administration induced decreased food and lipid intakes in all age groups. These results suggest that GHRH may regulate feeding through pituitary and/or hypothalamic GHRH receptor mechanisms.
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Affiliation(s)
- C Veyrat-Durebex
- Laboratoire de Neuroendocrinologie du vieillissement, Université Blaise Pascal, 63177, Aubière, France
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Castilla-Cortázar I, Aliaga-Montilla MA, Salvador J, García M, Delgado G, González-Barón S, Quiroga J, Prieto J. Insulin-like growth factor-I restores the reduced somatostatinergic tone controlling growth hormone secretion in cirrhotic rats. LIVER 2001; 21:405-9. [PMID: 11903885 DOI: 10.1034/j.1600-0676.2001.210607.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
BACKGROUND/AIMS An altered growth hormone/insulin-like growth factor-I (GH/IGF-I) axis occurs in advanced liver cirrhosis, characterised by diminished serum levels of IGF-I and increased concentrations of GH. Under normal conditions, GH release is mediated by somatostatin (SS) inhibition. However, the influence of SS on GH release in cirrhosis is not well known. IGF-I supplementation has beneficial effects in experimental cirrhosis, and - under physiological conditions - IGF-I increases SS, inhibiting GH. The aims of this work were to study SS tone in cirrhotic animals and to evaluate whether IGF-I treatment influences SS tone, controlling GH secretion in cirrhosis. METHODS We studied the influence of SS on GH secretion by assessing GH response to pyridostigmine (PD) in cirrhotic rats treated and untreated with IGF-I. Liver cirrhosis was induced with CCl4-inhalation for 11 weeks in male Wistar rats. The animals were randomly divided into two groups: CI+IGF (n=12), which received IGF-I treatment for 12 days (2 microg/100 g body wt-1 x d-1) and CI (n=12), which received saline. Healthy controls (CO, n=12) were studied at the same time. On day 13, animals from each group were subdivided into two groups (n=6) in order to explore the effect of a PD intrajugular bolus (10 microg x 100 gbw-1) on serum GH levels (at 0,10,20,30 and 60 min), which were assessed by RIA. RESULTS PD bolus did not exert any effect on GH serum levels in the CI group, suggesting a low SS tone in cirrhotic rats. However, PD induced an increase in GH levels into CO and CI+IGF groups. In conclusion, as occurs under normal conditions, the cholinergic system is a significant modulator of GH secretion in experimental liver cirrhosis. CONCLUSION Cirrhotic rats have a reduced somatostatinergic tone which can be restored by IGF-I supplementation, suggesting that somatostatin is the main factor involved in the feed-back regulation between GH and IGF-I in cirrhosis.
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Affiliation(s)
- I Castilla-Cortázar
- Departments of Human Physiology,Endocrinology and Internal Medicine, Liver Unit, University of Navarra, Pamplona, Spain.
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Gianotti L, Maccario M, Lanfranco F, Ramunni J, Di Vito L, Grottoli S, Muller EE, Ghigo E, Arvat E. Arginine counteracts the inhibitory effect of recombinant human insulin-like growth factor I on the somatotroph responsiveness to growth hormone-releasing hormone in humans. J Clin Endocrinol Metab 2000; 85:3604-8. [PMID: 11061509 DOI: 10.1210/jcem.85.10.6872] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Insulin-like growth factor I (IGF-I) exerts a negative feedback effect on GH secretion via either direct actions at the pituitary level or indirect ones at the hypothalamic level, through stimulation of somatostatin (SS) and/or inhibition of GHRH release. In fact, recombinant human IGF-I (rhIGF-I) in humans inhibits spontaneous GH secretion as well as the GH response to GHRH and even more to GH/GH-releasing peptides, whose main action is on the hypothalamus, antagonizing SS and enhancing GHRH activity. The aim of the present study was to further clarify in humans the mechanisms underlying IGF-I-induced inhibition of somatotroph secretion. In six normal young volunteers (all women; mean +/- SEM: age, 28.3+/-1.2 yr; body mass index, 21.3+/-1.2 kg/m2) we studied the GH response to GHRH (1 microg/kg, iv, at 0 min), both alone and combined with arginine (ARG; 0.5 g/kg, iv, from 0-30 min), which probably acts via inhibition of hypothalamic SS release, after pretreatment with rhIGF-I (20 microg/kg, sc, at -180 min) or placebo. rhIGF-I increased circulating IGF-I levels (peak at -60 vs. -180 min: 54.9+/-3.9 vs. 35.9+/-3.3 mmol/L; P < 0.05) to a reproducible extent, and these levels remained stable and within the normal range until 90 min. The mean GH concentration over 3 h (from -180 to 0 min) before ARG and/or GHRH was not modified by placebo or rhIGF-I. After placebo, the GH response to GHRH (peak, 23.6+/-2.9 microg/L) was strikingly enhanced (P < 0.05) by ARG coadministration (69.6+/-9.9 microg/L). rhIGF-I blunted the GH response to GHRH (13.1+/-4.5 microg/L; P < 0.05), whereas that to GHRH plus ARG was not modified (59.5+/-8.9 microg/L), although it occurred with some delay. Mean glucose and insulin concentrations were not modified by either placebo or rhIGF-I. In conclusion, ARG counteracts the inhibitory effect of rhIGF-I on somatotroph responsiveness to GHRH in humans. These findings suggest that the acute inhibitory effect of rhIGF-I on the GH response to GHRH takes place on the hypothalamus, possibly via enhancement of SS release, and that ARG overrides this action.
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Affiliation(s)
- L Gianotti
- Department of Internal Medicine, University of Turin, Italy
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21
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Rollo CD, Kajiura LJ, Wylie B, D'Souza S. The growth hormone axis, feeding, and central allocative regulation: lessons from giant transgenic growth hormone mice. CAN J ZOOL 1999. [DOI: 10.1139/z99-162] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Lifetime consumption rates of male transgenic growth hormone (GH) mice and normal controls were measured on either a 38% protein diet (HP), the standard rodent diet (STD) (23.5% protein), or the standard diet supplemented with a free choice of sucrose (CARB). On STD, daily intake of normal mice increased little at sizes greater than 20 g, but larger transgenic mice ate progressively more. Both kinds of mice showed declining daily mass-specific consumption with increasing age. Transgenic mice consistently ate 13.3% less food than normal mice on a mass-specific basis across all ages. On the self-selective CARB diet, normal mice exhibited increasing age-specific daily consumption, whereas transgenic mice exhibited a trend towards age-related decline in mass-specific feeding that proved significant on the basis of body mass. Transgenic mice ingested more sucrose than standard chow and this did not vary with age. In contrast, normal mice ate less sucrose than chow and chose a declining proportion of sucrose with age. Transgenic and normal mice showed a unitary relationship of daily intake of HP in relation to body mass, resulting in constant mass-specific feeding across all ages. Transgenic GH animals, including livestock, show numerous defects that we have attributed to relative energetic stress associated with excessive allocation to lean growth. This is exacerbated by failure to offset increased demands of growth by increasing mass-specific feeding. Results presented here document altered feeding regulation in transgenic GH mice and suggest underlying mechanisms.
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Abstract
The secretion of growth hormone (GH) is regulated through a complex neuroendocrine control system, especially by the functional interplay of two hypothalamic hypophysiotropic hormones, GH-releasing hormone (GHRH) and somatostatin (SS), exerting stimulatory and inhibitory influences, respectively, on the somatotrope. The two hypothalamic neurohormones are subject to modulation by a host of neurotransmitters, especially the noradrenergic and cholinergic ones and other hypothalamic neuropeptides, and are the final mediators of metabolic, endocrine, neural, and immune influences for the secretion of GH. Since the identification of the GHRH peptide, recombinant DNA procedures have been used to characterize the corresponding cDNA and to clone GHRH receptor isoforms in rodent and human pituitaries. Parallel to research into the effects of SS and its analogs on endocrine and exocrine secretions, investigations into their mechanism of action have led to the discovery of five separate SS receptor genes encoding a family of G protein-coupled SS receptors, which are widely expressed in the pituitary, brain, and the periphery, and to the synthesis of analogs with subtype specificity. Better understanding of the function of GHRH, SS, and their receptors and, hence, of neural regulation of GH secretion in health and disease has been achieved with the discovery of a new class of fairly specific, orally active, small peptides and their congeners, the GH-releasing peptides, acting on specific, ubiquitous seven-transmembrane domain receptors, whose natural ligands are not yet known.
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Affiliation(s)
- E E Müller
- Department of Pharmacology, Chemotherapy, and Toxicology, University of Milan, Milan, Italy
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Obál F, Kapás L, Gardi J, Taishi P, Bodosi B, Krueger JM. Insulin-like growth factor-1 (IGF-1)-induced inhibition of growth hormone secretion is associated with sleep suppression. Brain Res 1999; 818:267-74. [PMID: 10082812 DOI: 10.1016/s0006-8993(98)01286-4] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The hypothalamic growth hormone (GH)-releasing hormone (GHRH) promotes non-rapid eye movement sleep (NREMS). Insulin-like growth factor-1 (IGF-1) acts as a negative feedback in the somatotropic axis inhibiting GHRH and stimulating somatostatin. To determine whether this feedback alters sleep, rats and rabbits were injected intracerebroventricularly (i.c.v.) with IGF-1 (5.0 and 0.25 microgram, respectively) and the sleep-wake activity was studied. Compared to baseline (i.c.v. injection of physiological saline), IGF-1 elicited prompt suppressions in both NREMS and rapid eye movement sleep (REMS) in postinjection hour 1 in rats and rabbits. The intensity of NREMS (characterized by the slow wave activity of the EEG by means of fast-Fourier analysis) was significantly enhanced 7 to 11 h postinjection in rats. Plasma GH concentrations were measured in 30-min samples after i.c.v. IGF-1 injection in rats and a significant suppression of GH secretion was observed 30 min postinjection. The simultaneous inhibition of the somatotropic axis and sleep raises the possibility that the sleep alterations also result from an IGF-1-induced suppression of GHRH. The late increases in NREMS intensity are attributed to metabolic actions of IGF-1 or to a release of GHRH from the IGF-1-induced inhibition.
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Affiliation(s)
- F Obál
- Department of Physiology, A. Szent-Györgyi Medical University, 6720, Szeged, Hungary
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24
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Ghigo E, Gianotti L, Arvat E, Ramunni J, Valetto MR, Broglio F, Rolla M, Cavagnini F, Müller EE. Effects of recombinant human insulin-like growth factor I administration on growth hormone (GH) secretion, both spontaneous and stimulated by GH-releasing hormone or hexarelin, a peptidyl GH secretagogue, in humans. J Clin Endocrinol Metab 1999; 84:285-90. [PMID: 9920097 DOI: 10.1210/jcem.84.1.5386] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The negative feedback exerted by insulin-like growth factor I (IGF-I) on GH secretion occurs at the pituitary, as well as the hypothalamic level, via stimulation of SS and/or inhibition of GHRH release. In fact, recombinant human IGF-I (rhIGF-I) administration inhibits basal GH secretion, at least in fasted humans, though its effect on the GH response to GHRH is still controversial. GH secretagogues (GHS) are peptidyl and nonpeptidyl molecules that act on specific receptors at the pituitary and/or the hypothalamic level. Contrary to GHRH, the GH-releasing activity of GHS is strong, reproducible, and even partially refractory to inhibitory influences such as exogenous somatostatin. We studied the effects of rhIGF-I administration (20 microg/kg s.c. at 0 min) on GH secretion, either spontaneous or stimulated by GHRH (2 microg/kg i.v. at +180 min) or Hexarelin (HEX, 2.0 microg/kg i.v at +180 min), a GHS, in eight normal young women (age, mean +/- SEM, 28.3 +/- 1.2 yr; body mass index, 20.1 +/- 0.5 kg/m2). rhIGF-I administration increased IGF-I levels (peak vs. baseline: 420.3 +/- 30.5 vs. 274.4 +/- 25.3 microg/L, P < 0.05) within the physiological range from +120 to +300 min. No variation in glucose or insulin levels was recorded. rhIGF-I did not reduce spontaneous GH secretion [areas under curves (AUC)(0-300 min) 140.6 +/- 66.3 vs. 114.6 +/- 32.1 microg/L x h], whereas it inhibited the GH response to both GHRH (AUC(180-300 min) 447.7 +/- 159.4 vs. 715.9 +/- 104.3 microg/L x h, P < 0.05) and HEX (620.3 +/- 110.4 vs. 1705.9 +/- 328.9 microg/L x h, P < 0.03). The percent inhibitory effect of rhIGF-I on the GH response to GHRH (41.7 +/- 12.8%) was lower than that on the response to HEX (57.7 +/- 11.0%). In fact, the GH response to GHRH alone was clearly lower than that to HEX alone (P < 0.05), whereas the GH responses to GHRH and HEXwere similar after rhIGF-I. Our findings show that the sc administration of low rhIGF-I doses inhibits the GH response to GHRH and, even more, that to HEX; whereas, at least in this experimental design in fed conditions, it does not modify the spontaneous GH secretion. Because GHS generally show partial refractoriness to inhibitory inputs, including exogenous somatostatin, the present results point toward a peculiar sensitivity of GHS to the negative feedback action of IGF-I.
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Affiliation(s)
- E Ghigo
- Department of Internal Medicine, University of Turin, Italy
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