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Formenti AM, Maffezzoni F, Doga M, Mazziotti G, Giustina A. Growth hormone deficiency in treated acromegaly and active Cushing's syndrome. Best Pract Res Clin Endocrinol Metab 2017; 31:79-90. [PMID: 28477735 DOI: 10.1016/j.beem.2017.03.002] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Growth hormone deficiency (GHD) in adults is characterized by reduced quality of life and physical fitness, skeletal fragility, increased weight and cardiovascular risk. It may be found in (over-) treated acromegaly as well as in active Cushing's syndrome. Hypopituitarism may develop in patients after definitive treatment of acromegaly, although the exact prevalence of GHD in this population is still uncertain because of limited awareness, and scarce and conflicting data so far available. Because GHD associated with acromegaly and Cushing's syndrome may yield adverse consequences on similar target systems, the final outcomes of some complications of both acromegaly and Cushing's syndrome may be further affected by the occurrence of GHD. It is still largely unknown, however, whether GHD in patients with post-acromegaly or active Cushing's syndrome (e.g. pharmacologic glucocorticoid treatment) may benefit from GH replacement. We review the diagnostic, clinical and therapeutic aspects of GHD in adults treated for acromegaly and in those with active Cushing's syndrome.
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Affiliation(s)
| | | | - Mauro Doga
- Endocrinology, Univeristy of Brescia, Italy
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2
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Implication of corticotropic hormone axis in eating behaviour pattern in obese and type 2 diabetic participants. Br J Nutr 2015; 113:1237-43. [PMID: 25782454 DOI: 10.1017/s0007114515000549] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
In Algeria, eating behaviour has been increasingly deviated from its traditional Mediterranean diet to modern fast food style. The present study examines the interactions between eating behaviour pattern (EBP), corticotropic hormone axis and the metabolic syndrome. Our Algerian population cohort comprised of 410 participants (130 obese, 170 type 2 diabetics and 110 healthy participants). The EBP was evaluated by the Three-Factor Eating Questionnaire test. The anthropometric and metabolic parameters (glucose, TAG, HDL, LDL and cholesterol) and the concentrations of hormones (insulin, adrenocorticotropin hormone (ACTH), cortisol and growth hormone) were determined by biometrics, spectrophotometry and RIA, respectively. Multivariate analyses showed a high correlation between the EBP and the metabolic syndrome, particularly between insulin-resistant state and hypertrophy of visceral adipose tissue. Compared with healthy participants, obese ones showed the hyperphagic type of EBP, i.e. disinhibition and hunger disorders. Conversely, the diabetics showed both the hypophagic and hyperphagic type of EBP. In diabetic and obese participants, cortisol and ACTH secretions were significantly altered, leading to metabolic disorders. The present study confirms the role of EBP in obesity and diabetes.
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Giustina A, Mazziotti G. Impaired growth hormone secretion associated with low glucocorticoid levels: an experimental model for the Giustina effect. Endocrine 2014; 47:354-6. [PMID: 24798449 DOI: 10.1007/s12020-014-0278-y] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/10/2014] [Accepted: 04/18/2014] [Indexed: 12/26/2022]
Affiliation(s)
- Andrea Giustina
- University of Brescia, Poliambulatori di Via Biseo,Via Biseo 17, 25123, Brescia, Italy,
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4
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Nogami H, Yamamoto N, Hiraoka Y, Aiso S, Sugimoto K, Yoshida S, Shutoh F, Hisano S. Rapid induction of the growth hormone gene transcription by glucocorticoids in vitro: possible involvement of membrane glucocorticoid receptors and phosphatidylinositol 3-kinase activation. J Neuroendocrinol 2014; 26:195-204. [PMID: 24428719 DOI: 10.1111/jne.12132] [Citation(s) in RCA: 9] [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: 07/24/2013] [Revised: 12/19/2013] [Accepted: 01/07/2014] [Indexed: 12/25/2022]
Abstract
The regulation of transcription of the growth hormone (GH) gene by glucocorticoids was studied in MtT/S cells, a cell line derived from an oestrogen-induced mammotrophic tumour in the rat, and in the primary culture of the anterior pituitary gland of adult mice. The levels of the GH heteronuclear RNA (GH hnRNA), which are mainly determined by the transcription rate, increased by 25-fold during 24 h in response to dexamethasone (DEX; 1 μM) in MtT/S cells that were cultured in the medium containing charcoal-stripped serum for 7 days. The stimulatory effect of DEX on the GH hnRNA levels was detectable as early as 30 min. This rapid effect of DEX did not require on-going protein synthesis, whereas it was considered that DEX requires the presence of unknown cellular proteins produced independently of DEX stimulation. By contrast, on-going protein synthesis was required for DEX action when incubated for 6 h, as has been observed in the previous studies. The specific inhibitor of glucocorticoid receptor, RU486, inhibited both rapid (30 min) and delayed (6 h) the effects of glucocorticoids on GH hnRNA levels. Membrane impermeable glucocorticoid, corticosterone-bovine serum albumin conjugate (CSBSA), was found to have effects similar to those of DEX and free corticosterone (CS), suggesting that glucocorticoids regulate GH gene transcription at least in part through the membrane bound receptors. From pharmacological studies, it was suggested that phosphatidylinositol 3-kinase (PI3K) activation is involved in the rapid effects but not in the delayed effects of glucocorticoids. This also suggests that the delayed effects of glucocorticoids depend on mechanisms other than the activation of PI3-kinase. Finally, both rapid and delayed effects of CS and CSBSA were observed not only in MtT/S cells, but also in the mouse pituitary cells in primary culture. Therefore, it is possible that the membrane initiated action of glucocorticoids is involved in the regulation of GH transcription in normal pituitary cells, as well as in pituitary tumour cells.
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Affiliation(s)
- H Nogami
- Laboratry of Neuroendocrinology, Institute of Basic Medical Sciences, University of Tsukuba, Tsukuba, Ibaraki, Japan
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5
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Abstract
Glucocorticoids modulate the secretion of growth hormone (GH) by various and competing effects on the hypothalamus and pituitary gland. The final effects of this modulation depend on hormone concentrations and the duration of exposure. The traditional hypothesis is that chronically raised levels of glucocorticoids suppress the secretion of GH. However, a functional impairment of the GH reserve might also be observed in patients with low levels of glucocorticoids, such as those with secondary hypoadrenalism, which is consistent with the model of biphasic dose-dependent effects of glucocorticoids on the somatotropic axis. This Review updates our current understanding of the mechanisms underlying the effects of glucocorticoids on the secretion of GH and the clinical implications of the dual action of glucocorticoids on the GH reserve in humans. This Review will also address the potential diagnostic and therapeutic implications of GH for patients with a deficiency or excess of glucocorticoids.
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Affiliation(s)
- Gherardo Mazziotti
- Department of Medicine, Endocrine and Bone Unit, Azienda Ospedaliera Carlo Poma of Mantua, 46100 Mantua, Italy
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6
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Vakili H, Jin Y, Nagy JI, Cattini PA. Transgenic mice expressing the human growth hormone gene provide a model system to study human growth hormone synthesis and secretion in non-tumor-derived pituitary cells: differential effects of dexamethasone and thyroid hormone. Mol Cell Endocrinol 2011; 345:48-57. [PMID: 21777655 DOI: 10.1016/j.mce.2011.07.010] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/27/2011] [Revised: 06/14/2011] [Accepted: 07/05/2011] [Indexed: 11/17/2022]
Abstract
Growth hormone (GH) is regulated by pituitary and hypothalamic factors as well as peripheral endocrine factors including glucocorticoids and thyroid hormone. Studies on human GH are limited largely to the assessment of plasma levels in endocrine disorders. Thus, insight into the regulation of synthesis versus secretion has come mainly from studies done on non-human GH and/or pituitary tumor cells. However, primate and non-primate GH gene loci have differences in their structure and, by extension, regulation. We generated transgenic (171hGH/CS-TG) mice containing the intact hGH1 gene and locus control region, including sequences required for integration-independent and preferential pituitary expression. Here, we show hGH co-localizes with mouse (m) GH in somatotrophs in situ and in primary pituitary cells. Dexamethasone treatment increased hGH and mGH, as well as GH releasing hormone (GHRH) receptor RNA levels, and hGH release was stimulated by GHRH treatment. By contrast, triiodothyronine decreased or had no effect on hGH and mGH production, respectively, and the negative effect on hGH was also seen in the presence of dexamethasone. Thus, 171hGH/CS-TG mouse pituitary cultures represent a model system to investigate hormonal control of hGH synthesis and secretion.
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MESH Headings
- Animals
- Cells, Cultured
- Dexamethasone/pharmacology
- Female
- Ghrelin/pharmacology
- Growth Hormone-Releasing Hormone/pharmacology
- Human Growth Hormone/genetics
- Human Growth Hormone/metabolism
- Humans
- Immunohistochemistry
- Male
- Mice
- Mice, Transgenic
- Models, Biological
- Pituitary Gland/cytology
- Pituitary Gland/drug effects
- Pituitary Gland/metabolism
- RNA, Messenger/genetics
- RNA, Messenger/metabolism
- Receptors, Ghrelin/genetics
- Receptors, Ghrelin/metabolism
- Receptors, Neuropeptide/genetics
- Receptors, Neuropeptide/metabolism
- Receptors, Pituitary Hormone-Regulating Hormone/genetics
- Receptors, Pituitary Hormone-Regulating Hormone/metabolism
- Thyroid Hormones/pharmacology
- Triiodothyronine/pharmacology
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Affiliation(s)
- Hana Vakili
- Department of Physiology, University of Manitoba, Canada
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7
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Luque RM, Gahete MD, Cordoba-Chacon J, Childs GV, Kineman RD. Does the pituitary somatotrope play a primary role in regulating GH output in metabolic extremes? Ann N Y Acad Sci 2011; 1220:82-92. [PMID: 21388406 DOI: 10.1111/j.1749-6632.2010.05913.x] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Circulating growth hormone (GH) levels rise in response to nutrient deprivation and fall in states of nutrient excess. Because GH regulates carbohydrate, lipid, and protein metabolism, defining the mechanisms by which changes in metabolism alter GH secretion will aid in our understanding of the cause, progression, and treatment of metabolic diseases. This review will summarize what is currently known regarding the impact of systemic metabolic signals on GH-axis function. In addition, ongoing studies using the Cre/loxP system to generate mouse models with selective somatotrope resistance to metabolic signals will be discussed, where these models will serve to enhance our understanding of the specific role the somatotrope plays in sensing the metabolic environment and adjusting GH output in metabolic extremes.
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Affiliation(s)
- Raul M Luque
- Department of Cell Biology, Physiology and Immunology, University of Cordoba, Instituto Maimónides de Investigación Biomédica de Córdoba, CIBER Fisiopatología de la Obesidad y Nutrición, Córdoba, Spain
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8
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Cornford AS, Barkan AL, Horowitz JF. Rapid suppression of growth hormone concentration by overeating: potential mediation by hyperinsulinemia. J Clin Endocrinol Metab 2011; 96:824-30. [PMID: 21209037 PMCID: PMC3047219 DOI: 10.1210/jc.2010-1895] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
CONTEXT The very low GH concentration in obesity is commonly attributed to high body fat mass; however, the influence of overeating on GH secretion is not clear. OBJECTIVE The aim of the study was to examine the effects of 2 wk of overeating on changes in GH secretion. SETTING Subjects were admitted to the hospital and stayed within the Michigan Clinical Research Unit throughout the entire 2-wk overeating period. PARTICIPANTS We studied seven healthy, nonobese men (body mass index, 24 ± 1 kg/m(2); age, 25 ± 1 yr). INTERVENTION Subjects ate standardized meals containing 70 kcal/kg fat free mass/d (∼4000 kcal/d) for 2 wk. MAIN OUTCOME MEASURES Twenty-four-hour plasma concentrations of GH (every 20 min) and insulin (every 2 h) were measured before overeating (baseline), on d 3, and after 2 wk of overeating. RESULTS Compared with baseline, average 24-h plasma GH concentration declined nearly 80% by d 3 of overeating (1.30 ± 0.18 vs. 0.36 ± 0.09 ng/ml; P = 0.01). This marked suppression of GH secretion occurred in the absence of an increase in body weight (77.0 ± 2.2 vs. 76.4 ± 2.4 kg). At the same time, average 24-h insulin concentration doubled (16.6 ± 2.1 vs. 31.7 ± 5.8 μU/ml; P = 0.009). After 2 wk, body weight significantly increased (79.0 ± 2.1 kg; P < 0.001), and body fat increased by more than 10% (P = 0.002). However, this did not induce a further suppression in plasma GH concentration (0.33 ± 0.08 ng/ml). CONCLUSION Only a few days of overeating markedly suppressed GH secretion before any measurable weight gain and was accompanied by chronic hyperinsulinemia. Increased body weight and body fat by 2 wk of overeating did not further suppress GH secretion.
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Affiliation(s)
- Andrea S Cornford
- School of Kinesiology, University of Michigan, 401 Washtenaw Avenue, Ann Arbor, Michigan 48109-2214, USA
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9
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Effects of long-term dietary interventions on pituitary growth hormone-releasing hormone receptor in aging rats and potential mechanisms of action. Mech Ageing Dev 2010; 131:169-78. [DOI: 10.1016/j.mad.2010.01.003] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2009] [Revised: 12/23/2009] [Accepted: 01/09/2010] [Indexed: 11/19/2022]
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10
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Wójcikowski J, Daniel WA. The brain dopaminergic system as an important center regulating liver cytochrome P450 in the rat. Expert Opin Drug Metab Toxicol 2009; 5:631-45. [DOI: 10.1517/17425250902973703] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
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11
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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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12
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Wójcikowski J, Gołembiowska K, Daniel WA. Regulation of liver cytochrome P450 by activation of brain dopaminergic system: Physiological and pharmacological implications. Biochem Pharmacol 2008; 76:258-67. [DOI: 10.1016/j.bcp.2008.04.016] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2008] [Revised: 04/25/2008] [Accepted: 04/25/2008] [Indexed: 11/25/2022]
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13
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Bédard K, Strecko J, Thériault K, Bédard J, Veyrat-Durebex C, Gaudreau P. Effects of a high-glucose environment on the pituitary growth hormone-releasing hormone receptor: type 1 diabetes compared with in vitro glucotoxicity. Am J Physiol Endocrinol Metab 2008; 294:E740-51. [PMID: 18285528 DOI: 10.1152/ajpendo.00141.2007] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The present study investigated the effects of diabetes and high glucose on GHRH receptor (GHRH-R) mRNA and protein levels in the pituitary of diabetic rats 2, 21, and 60 days post-streptozotocin (post-STZ) administration. Two days post-STZ, the 2.5-kb GHRH-R mRNA transcript was increased. Twenty-one days post-STZ, both the 2.5- and 4-kb transcripts and a 72-kDa (125)I-GHRH-GHRH-R complex were elevated. Sixty days post-STZ, the 4-kb transcript remained increased and the 45-kDa (125)I-GHRH-GHRH-R complex (functional receptor) was decreased. Hypothalamic GHRH mRNA and serum total IGF-I levels were reduced at all three time points. To better understand the role of high glucose on GHRH-R regulation, time-course effects of 33 compared with 6 mM d-glucose (DG) were examined in cultured anterior pituitary cells from 2-mo-old healthy rats. Membrane lipoperoxidation was present in 33 mM DG, and GHRH-R mRNA levels were diminished after 24 h, Fluo-GHRH internalization was marginal after 16-24 h, and GHRH-induced cAMP levels were decreased after 24 and 48 h. Altogether, these results indicate that the increase of the 2.5-kb GHRH-R mRNA transcript in vivo could be a consequence of a decrease of hypothalamic GHRH mRNA levels in STZ rats. Since it does not affect primarily functional GHRH-R levels, the initial diminution of circulating IGF-I levels could result from a decreased GHRH-R stimulation by GHRH. Thus, the effect of glucotoxicity would be related to a decrease of functional GHRH-R protein, as observed in rats 60 days post-STZ and in cultured pituitary cells from healthy rats exposed to a high-glucose environment.
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MESH Headings
- Animals
- Apoptosis/drug effects
- Apoptosis/physiology
- Cells, Cultured
- Cyclic AMP/metabolism
- Diabetes Mellitus, Experimental/metabolism
- Diabetes Mellitus, Experimental/physiopathology
- Diabetes Mellitus, Type 1/metabolism
- Diabetes Mellitus, Type 1/physiopathology
- Fluoresceins
- Glucose/toxicity
- Growth Hormone-Releasing Hormone/metabolism
- In Vitro Techniques
- Insulin-Like Growth Factor I/metabolism
- Iodine Radioisotopes
- Lipid Peroxidation/drug effects
- Lipid Peroxidation/physiology
- Male
- Necrosis
- Oxidative Stress/drug effects
- Oxidative Stress/physiology
- Pituitary Gland, Anterior/cytology
- Pituitary Gland, Anterior/drug effects
- Pituitary Gland, Anterior/physiology
- RNA, Messenger/metabolism
- Radioligand Assay
- Rats
- Rats, Sprague-Dawley
- Receptors, Neuropeptide/genetics
- Receptors, Neuropeptide/metabolism
- Receptors, Pituitary Hormone-Regulating Hormone/genetics
- Receptors, Pituitary Hormone-Regulating Hormone/metabolism
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Affiliation(s)
- Karine Bédard
- Laboratory of Neuroendocrinology of Aging, Centre hospitalier de l'Université de Montréal Research Center, and Department of Medicine, University of Montreal, Montreal, Quebec, Canada
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14
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McElvaine AT, Korytko AI, Kilen SM, Cuttler L, Mayo KE. Pituitary-Specific Expression and Pit-1 Regulation of the Rat Growth Hormone-Releasing Hormone Receptor Gene. Mol Endocrinol 2007; 21:1969-83. [PMID: 17536003 DOI: 10.1210/me.2007-0116] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
The GHRH receptor is expressed in the somatotroph cell of the anterior pituitary, where it functions to mediate GHRH-stimulated GH release. To study pituitary and somatotroph cell-specific expression of this gene, a transgenic mouse model and complementary cell culture experiments were developed. The activity of the 1.6-kb proximal rat GHRH receptor promoter was examined in vivo by generating transgenic mice with the promoter directing expression of a luciferase reporter. The promoter directs tissue-specific expression; luciferase is highly expressed in the pituitary but absent from 14 other tissues. Immunocytochemistry experiments show that transgene expression is targeted to GH-expressing somatotroph cells. The transgene is 5-fold more highly expressed in males than females, and there is an increase in transgene expression leading up to the onset of puberty. The 1.6-kb promoter was further examined in cell culture experiments, which revealed that the promoter is selectively activated in pituitary cells and that promoter-reporter expression in nonpituitary cells can be enhanced by the pituitary-specific transcription factor Pit-1. EMSAs identified 10 short regions that specifically bind Pit-1 with highly variable relative affinities. The highest affinity site was previously identified and is required for Pit-1 activation of the promoter. Four additional sites contribute to Pit-1 regulation of the promoter and are important to achieving full activation of the gene. The results show that the 1.6-kb promoter is sufficient to direct tissue- and cell-specific expression in vivo and is regulated by Pit-1.
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Affiliation(s)
- Allison T McElvaine
- Department of Biochemistry, Molecular Biology, and Cell Biology, Northwestern University, Hogan 4-112, Evanston, Illinois 60208, USA
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15
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Kwok AHY, Wang Y, Wang CY, Leung FC. Cloning of Chicken Glucocorticoid Receptor (GR) and Characterization of its Expression in Pituitary and Extrapituitary Tissues. Poult Sci 2007; 86:423-30. [PMID: 17234861 DOI: 10.1093/ps/86.2.423] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Substantial evidence suggests that glucocorticoids play critical roles in the differentiation of somatotroph and lactotroph in embryonic pituitaries of birds. However, the basic information on the expression of glucocorticoid receptor (GR) in avian species is limited. In this study, the full-length cDNA for chicken GR was cloned from the chicken kidney. It encodes 772 amino acids and shares high homology with that of the human (73%), mouse (73%), rat (71%), rabbit (72%), and trout (51%) sequences. Similar to mammals, chicken GR is widely expressed in all adult tissues being investigated. Among the 12 tissues investigated, relatively high expression of GR was detected in pituitary, muscle, ovary, and kidney using reverse transcription-PCR assay. Using semiquantitative reverse transcription-PCR, GR is shown to be abundantly expressed at a more or less constant level during embryonic pituitary development (from d 8 to 20), supporting the hypothesis that the expression of GR is unlikely to be a limiting factor in initiating the differentiation of somatotroph and lactotroph in embryonic pituitary of birds. Moreover, an abundant expression of GR in the whole embryos at earlier developmental stages (from d 2 to 5) was also detected in the present study, though its physiological relevance remains to be determined.
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Affiliation(s)
- A H Y Kwok
- Department of Zoology, The University of Hong Kong, Hong Kong, China
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16
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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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17
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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: 0.8] [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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18
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Porter TE, Ellestad LE, Fay A, Stewart JL, Bossis I. Identification of the chicken growth hormone-releasing hormone receptor (GHRH-R) mRNA and gene: regulation of anterior pituitary GHRH-R mRNA levels by homologous and heterologous hormones. Endocrinology 2006; 147:2535-43. [PMID: 16469800 DOI: 10.1210/en.2005-1534] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
GHRH stimulates GH secretion in chickens as in mammals. However, nothing is known about the chicken GHRH receptor (GHRH-R). Here we report the cDNA sequence of chicken GHRH-R. Comparison of the cDNA sequence with the chicken genome localized the GHRH-R gene to chicken chromosome 2 and indicated that the chicken GHRH-R gene consists of 13 exons. Expression of all exons was confirmed by RT-PCR amplification of pituitary mRNA. The amino acid sequence predicted by the GHRH-R cDNA is homologous to that in other vertebrates and contains seven transmembrane domains and a conserved hormone-binding domain. The predicted size of the GHRH-R protein (48.9 kDa) was confirmed by binding of (125)I-GHRH to chicken pituitary membranes and SDS-PAGE. GHRH-R mRNA was readily detected by RT-PCR in the pituitary but not in the hypothalamus, total brain, lung, adrenal, ovary, or pineal gland. Effects of corticosterone (CORT), GHRH, ghrelin, pituitary adenylate cyclase-activating peptide, somatostatin (SRIF), and TRH on GHRH-R and GH gene expression were determined in cultures of chicken anterior pituitary cells. GHRH-R and GH mRNA levels were determined by quantitative real-time RT-PCR. Whereas all treatments affected levels of GH mRNA, only CORT, GHRH, and SRIF significantly altered GHRH-R mRNA levels. GHRH-R gene expression was modestly increased by GHRH and suppressed by SRIF at 4 h, and CORT dramatically decreased levels of GHRH-R mRNA at 72 h. We conclude that adrenal glucocorticoids may substantially impact pituitary GH responses to GHRH in the chicken through modulation of GHRH-R gene expression.
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MESH Headings
- Amino Acid Sequence
- Animals
- Brain/embryology
- Cells, Cultured
- Chickens
- Chromosome Mapping
- Computational Biology
- Cross-Linking Reagents/pharmacology
- DNA Primers/chemistry
- DNA, Complementary/metabolism
- Dose-Response Relationship, Drug
- Electrophoresis, Polyacrylamide Gel
- Exons
- Female
- Gene Expression Regulation
- Gene Library
- Hypothalamus/metabolism
- Introns
- Molecular Sequence Data
- Molecular Weight
- Phylogeny
- Protein Binding
- Protein Structure, Tertiary
- RNA, Messenger/metabolism
- Receptors, Neuropeptide/genetics
- Receptors, Neuropeptide/physiology
- Receptors, Pituitary Hormone-Regulating Hormone/genetics
- Receptors, Pituitary Hormone-Regulating Hormone/physiology
- Reverse Transcriptase Polymerase Chain Reaction
- Sequence Analysis, DNA
- Sequence Homology, Amino Acid
- Time Factors
- Tissue Distribution
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Affiliation(s)
- Tom E Porter
- Department of Animal and Avian Sciences, University of Maryland, College Park, 20742, USA
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19
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van Aken MO, Pereira AM, Frölich M, Romijn JA, Pijl H, Veldhuis JD, Roelfsema F. Growth hormone secretion in primary adrenal Cushing's syndrome is disorderly and inversely correlated with body mass index. Am J Physiol Endocrinol Metab 2005; 288:E63-70. [PMID: 15328071 DOI: 10.1152/ajpendo.00317.2004] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
To evaluate the impact on the somatotropic axis of endogenous cortisol excess in the absence of primary pituitary disease, we investigated spontaneous 24-h growth hormone (GH) secretion in 12 adult patients with ACTH-independent hypercortisolism. Plasma GH concentration profiles (10-min samples) were analyzed by deconvolution to reconstruct secretion and approximate entropy to quantitate orderliness of the release process. Comparisons were made with a body mass index (BMI)-, age-, and gender-matched control group and an age- and gender-matched lean control group. GH secretion rates did not differ from BMI-matched controls but were twofold lower compared with lean subjects, mainly due to a 2.5-fold attenuation of the mean secretory burst mass (P = 0.001). In hypercortisolemic patients, GH secretion was negatively correlated with BMI (R = -0.55, P = 0.005) but not cortisol secretion. Total serum IGF-I concentrations were similar in the three groups. Approximate entropy (ApEn) was increased in patients with Cushing's syndrome compared with both control groups (vs. BMI-matched, P = 0.04; vs. lean, P = 0.001), denoting more irregular GH secretion patterns. ApEn in patients correlated directly with cortisol secretion (R = 0.77, P = 0.003). Synchrony between cortisol and GH concentration series was analyzed by cross-correlation, cross-ApEn, and copulsatility analyses. Patients showed loss of pattern synchrony compared with BMI-matched controls, but copulsatility was unchanged. We conclude that hyposomatotropism in primary adrenal hypercortisolism is only partly explained (approximately 30%) by increased body weight and that increased GH secretory irregularity and loss of synchrony suggest altered coordinate regulation of GH release.
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Affiliation(s)
- Maarten O van Aken
- Department of Endocrinology and Metabolic Diseases, Leiden University Medical Center, Leiden, The Netherlands
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20
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Park S, Peng XD, Frohman LA, Kineman RD. Expression analysis of hypothalamic and pituitary components of the growth hormone axis in fasted and streptozotocin-treated neuropeptide Y (NPY)-intact (NPY+/+) and NPY-knockout (NPY-/-) mice. Neuroendocrinology 2005; 81:360-71. [PMID: 16244497 DOI: 10.1159/000089101] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/26/2005] [Accepted: 08/29/2005] [Indexed: 01/08/2023]
Abstract
In the fasted and the streptozotocin (STZ)-induced diabetic male rat, hypothalamic growth hormone (GH)-releasing hormone (GHRH) mRNA levels, and pulsatile GH release are decreased. These changes are believed to be due to a rise in hypothalamic neuropeptide Y (NPY) that inhibits GHRH expression. To directly test if NPY is required for metabolic regulation of hypothalamic neuropeptides important in GH secretion, NPY, GHRH and somatostatin (SRIH) mRNA levels were determined in fasted (48 h) and STZ-treated wild-type (NPY(+/+)) and NPY-knockout (NPY(-/-)) mice by ribonuclease protection assay. In addition, pituitary receptor mRNA levels for GHRH (GHRH-R), ghrelin (GHS-R) and SRIH (sst2) were assessed by RT-PCR. Under fed conditions the GH axis of NPY(+/+) and NPY(-/-) did not differ. In the NPY(+/+) mouse, fasting resulted in a 23% weight loss and >250% increase in NPY mRNA accompanied by a significant reduction in both GHRH and SRIH mRNA. These changes were associated with increases in pituitary expression of GHRH-R and GHS-R and a concomitant suppression of sst2. In the NPY(-/-) mouse, fasting also resulted in a 23% weight loss and comparable changes in GHRH-R and sst2, but failed to alter GHRH, SRIH and GHS-R mRNA levels. Fasting resulted in an overall increase in circulating GH, which reached significance in the fasted NPY(-/-) mouse. Induction of diabetes in NPY(+/+) mice, using a single, high-dose, STZ injection (150 mg/kg), resulted in modest weight loss (5%), and a 158% increase NPY expression which was associated with reciprocal changes in pituitary GHS-R and sst2 expression, similar to that observed in the fasted state, but no change in hypothalamic GHRH or SRIF expression was observed. Induction of diabetes in NPY(+/+) and NPY(-/-) mice, using a multiple, low-dose, STZ paradigm (5 consecutive daily injections of 40 mg/kg), did not alter body weight, hypothalamic neuropeptide expression or pituitary receptor expression, with the exception that sst2 mRNA levels were suppressed and GH levels did rise in the NPY(-/-) mouse. These observations demonstrate that NPY is not required for basal regulation of the GH axis, but is required for fasting-induced suppression of GHRH and SRIH expression, as well as fasting-induced augmentation of pituitary GHS-R mRNA. In contrast to the rat, fasting clearly did not suppress circulating GH levels in mice, but resulted in an overall rise in mean GH levels, similar to that observed in other mammalian species. The fact that many of the fasting-induced changes in the GH axis were observed in the high-dose STZ-treated mice, but were not observed in the multiple, low-dose paradigm, suggests STZ-mediated modulation of GH axis function is dependent on the severity of the catabolic state and not hyperglycemia.
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Affiliation(s)
- Seungjoon Park
- Section of Endocrinology and Metabolism, Department of Medicine, University of Illinois at Chicago, 820 Damen Avenue, Chicago, IL 60612, USA
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21
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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: 2.5] [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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22
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23
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Affiliation(s)
- Karen Lin-Su
- Division of Pediatric Endocrinology, Weill Medical College of Cornell University, New York, USA
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24
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Nogami H, Hiraoka Y, Matsubara M, Nonobe E, Harigaya T, Katayama M, Hemmi N, Kobayashi S, Mogi K, Aiso S, Kawamura K, Hisano S. A composite hormone response element regulates transcription of the rat GHRH receptor gene. Endocrinology 2002; 143:1318-26. [PMID: 11897688 DOI: 10.1210/endo.143.4.8710] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
To further elucidate the molecular mechanisms underlying the transcriptional regulation of the GHRH receptor (GHRH-R) gene, hormonal regulation of the promoter activity of this gene was examined. An approximately 3-kb genomic fragment spanning the promoter region of the gene was sequenced and the transcription start site was determined by RT-PCR and RNase protection assay. A major start site was localized at -105 (relative to the translation initiation codon, ATG), and a pit-1 binding sequence characteristic of pituitary specific genes was found at -155 to -146. Deletion and mutation studies demonstrated this site to be functional. In the presence of dexamethasone, the GHRH-R promoter (from -2935 to -11) directed luciferase expression in MtT-S cells, a somatotropic cell line, but not in the PC12 cells that normally do not express GHRH-R. While T(3), all trans-RA, and 9cis-RA alone weakly enhanced the reporter gene expression, each of these substances was found to act as a synergistic enhancer in the presence of dexamethasone. Additional deletion and mutation analyses demonstrated a functional RA response element at -1090 to -1074. Two functional glucocorticoid response elements and a T(3) response element were found in an 80-bp 5'-flanking sequence of the pit-1 site. Interestingly, it is suggested that the 6-bp half-site AGGACA (from -209 to -204) functions as a 3'-half-site of T(3) response element as well as a 5'-half-site of one of the glucocorticoid response elements.
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Affiliation(s)
- Haruo Nogami
- Department of Neuroendocrinology, Basic Medical Sciences, University of Tsukuba, Tsukuba 305-8575, Japan.
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25
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Kovacs M, Schally AV, Csernus B, Busto R, Rekasi Z, Nagy A. Targeted cytotoxic analogue of luteinizing hormone-releasing hormone (LH-RH) only transiently decreases the gene expression of pituitary receptors for LH-RH. J Neuroendocrinol 2002; 14:5-13. [PMID: 11903807 DOI: 10.1046/j.0007-1331.2001.00728.x] [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] [Indexed: 11/20/2022]
Abstract
A cytotoxic analogue of LH-RH, AN-207, consisting of 2-pyrrolinodoxorubicin (AN-201) linked to carrier [D-Lys6]LH-RH, was developed for targeted therapy of cancers expressing LH-RH-receptors. To determine its possible side-effects on the pituitary gland, we investigated the gene expression of pituitary LH-RH-receptors and LH secretion in ovariectomized female and normal male rats after treatment with the maximum tolerated dose of AN-207. The effect of AN-207 on the gene expression of the pituitary GH-RH-receptors and GH secretion was also assessed in male rats. Five hours after a single i.v. injection of AN-207 at 175 nmol/kg, there was a 39-51% decrease in mRNA expression for the pituitary LH-RH-receptors in male and female rats. The carrier, at an equimolar dose, caused a similar reduction (37-39%), whereas the cytotoxic radical AN-201, at an equitoxic dose (110 nmol/kg), produced only a 12-24% decrease (NS) in the mRNA expression of LH-RH-receptors. AN-207 and the carrier analogue induced a comparable 90-100-fold increase in serum LH concentrations in male rats, and the same 12-fold elevation in OVX rats at 5 h. Seven days after treatment with AN-207, the mRNA levels for the LH-RH receptors and the serum LH concentration were back to normal in both sexes. AN-207, the carrier, and AN-201 had no significant effect on the expression of mRNA for GH-RH-receptors in the pituitary. In vitro, a continuous perfusion of pituitary cells with 10 nM AN-207 did not affect the hormone-releasing function of the targeted LH cells or the nontargeted GH cells. Our results demonstrate that cytotoxic LH-RH analogue AN-207, at the maximum tolerated dose causes only a transient decrease in the gene expression of the pituitary LH-RH receptors, and the levels of mRNA for LH-RH receptor fully recover within 7 days. Moreover, the carrier hormone moiety, and not the cytotoxic radical in AN-207 is responsible for this transient suppression. Our findings suggest that the therapy with cytotoxic LH-RH analogues will not inflict permanent damage to pituitary function.
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Affiliation(s)
- M Kovacs
- Endocrine, Polypeptide, and Cancer Institute, Veterans Affairs Medical Center, New Orleans, LA 70112, USA
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26
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Korytko AI, Cuttler L. Regulation of GHRH receptor gene expression in the neonatal and adult rat pituitary. Growth Horm IGF Res 2001; 11:282-288. [PMID: 11735246 DOI: 10.1054/ghir.2001.0238] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The growth hormone releasing hormone (GHRH) receptor gene is essential for normal growth, and its expression is developmentally regulated. The factors that control GHRH receptor expression in the neonatal pituitary are not well understood. This study focuses on the regulation of GHRH receptor gene expression by thyroid hormone, glucocorticoids, insulin-like growth factor-I (IGF-I) and IGF-II in rat pituitary cell cultures. In newborn pituitaries, both T3 and hydrocortisone (24 h) caused a dose-dependent increase in GHRH receptor mRNA abundance, reaching levels 4.8-fold (P<0.001) and 6.5-fold (P<0.001) over corresponding controls. T3 and hydrocortisone also stimulated GHRH receptor expression in adult (70 day) pituitary cell cultures, consistent with our earlier findings. IGF-I treatment suppressed the inductive effects of T3 (P<0.02) and hydrocortisone (P<0.03) on GHRH receptor expression in adult pituitaries but not in neonatal pituitaries. Unlike IGF-I, IGF-II treatment had no effect on T3-induced or hydrocortisone-induced GHRH receptor expression in either neonates or adults. Taken together, these results indicate that (1) thyroid hormone and hydrocortisone act directly at the neonatal pituitary as potent stimulators of GHRH receptor gene expression, (2) IGF-I, but not IGF-II, acts at the pituitary to suppress GHRH receptor mRNA expression and (3) the effects of IGF-I on GHRH receptor gene expression are developmentally determined.
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Affiliation(s)
- A I Korytko
- Departments of Pediatrics and Pharmacology, Case Western Reserve University, School of Medicine, Cleveland, OH 44106, USA
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27
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Philip JG, John CD, Cover PO, Morris JF, Christian HC, Flower RJ, Buckingham JC. Opposing influences of glucocorticoids and interleukin-1beta on the secretion of growth hormone and ACTH in the rat in vivo: role of hypothalamic annexin 1. Br J Pharmacol 2001; 134:887-95. [PMID: 11606330 PMCID: PMC1573014 DOI: 10.1038/sj.bjp.0704324] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2001] [Revised: 07/17/2001] [Accepted: 08/03/2001] [Indexed: 01/01/2023] Open
Abstract
1. This study exploited established immunoneutralization protocols and an N-terminal annexin 1 peptide (annexin 1(Ac2 - 26)) to advance our knowledge of the role of annexin 1 as a mediator of acute glucocorticoid action in the rat neuroendocrine system in vivo. 2. Rats were treated with corticosterone (500 microg kg(-1), i.p.) or annexin 1(Ac2 - 26) (0.1 - 10 ng rat(-1), i.c.v.) and 75 min later with interleukin 1beta (IL-1beta, 10 ng rat(-1), i.c.v. or 500 microg kg(-1), i.p). Blood was collected 1 h later for hormone immunoassay. Where appropriate, anti-annexin 1 polyclonal antiserum (pAb) was administered subcutaneously or centrally prior to the steroid challenge. 3. Corticosterone did not affect the resting plasma corticotrophin (ACTH) concentration but suppressed the hypersecretion of ACTH induced by IL-1beta (i.p. or i.c.v.). Its actions were quenched by anti-annexin 1 pAb (s.c. or i.c.v) and mimicked by annexin 1(Ac2 - 26). 4. By contrast, corticosterone provoked an increase in serum growth hormone (GH) which was ablated by central but not peripheral administration of anti-annexin 1 pAb. IL-1beta (i.c.v. or i.p.) did not affect basal GH but, when given centrally but not peripherally, it abolished the corticosterone-induced hypersecretion of GH. Annexin 1(Ac2 - 26) (i.c.v.) also produced an increase in serum GH which was prevented by central injection of IL-1beta. 5. The results support the hypothesis that the acute regulatory actions of glucocorticoids on hypothalamo-pituitary-adrenocortical function require annexin 1. They also provide novel evidence that the positive influence of the steroids on GH secretion evident within this timeframe is effected centrally via an annexin 1-dependent mechanism which is antagonized by IL-1beta.
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Affiliation(s)
- J G Philip
- Department of Neuroendocrinology, Faculty of Medicine, Imperial College School of Science, Technology and Medicine, Commonwealth Building, Hammersmith Hospital Campus, Du Cane Road, London W12 0NN
| | - C D John
- Department of Neuroendocrinology, Faculty of Medicine, Imperial College School of Science, Technology and Medicine, Commonwealth Building, Hammersmith Hospital Campus, Du Cane Road, London W12 0NN
| | - P O Cover
- Department of Neuroendocrinology, Faculty of Medicine, Imperial College School of Science, Technology and Medicine, Commonwealth Building, Hammersmith Hospital Campus, Du Cane Road, London W12 0NN
| | - J F Morris
- Department of Human Anatomy & Genetics, University of Oxford, South Parks Road, Oxford OX1 3QX
| | - H C Christian
- Department of Human Anatomy & Genetics, University of Oxford, South Parks Road, Oxford OX1 3QX
| | - R J Flower
- Department of Biochemical Pharmacology, The William Harvey Research Institute, St Bartholomew's and the Royal London School of Medicine and Dentistry, Charterhouse Square, London EC1M 6BQ
| | - J C Buckingham
- Department of Neuroendocrinology, Faculty of Medicine, Imperial College School of Science, Technology and Medicine, Commonwealth Building, Hammersmith Hospital Campus, Du Cane Road, London W12 0NN
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28
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Wells T, Houston PA. Skeletal growth acceleration with growth hormone secretagogues in transgenic growth retarded rats: pattern-dependent effects and mechanisms of desensitization. J Neuroendocrinol 2001; 13:496-504. [PMID: 11412336 DOI: 10.1046/j.1365-2826.2001.00661.x] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The transgenic growth retarded (Tgr) rat is the first genetic model of growth hormone (GH) deficiency whose growth can be accelerated with exogenous GH secretagogues (GHSs). In this study, we have demonstrated that GHS-receptor (GHS-R) mRNA expression in the arcuate nucleus of Tgr rats was not significantly different to that in wild-type littermates. We have confirmed that GHS-induced elevation in body weight gain was accompanied by acceleration of skeletal growth, and that the effects of the GHS, GHRP-6, were both dose- and pattern-dependent. The growth response with continuous infusion of GHRP-6 was transient, accompanied by suppression of GH and corticosterone responses to bolus injection of GHRP-6. This desensitization occurred without downregulation of arcuate GHS-R mRNA expression, but was accompanied by elevated periventricular somatostatin mRNA expression. In contrast, pulsatile (3-hourly) infusion of GHRP-6 produced sustained growth and GH responses, which were accompanied by suppression of corticosterone responses and elevated arcuate GH-releasing factor (GRF) mRNA expression. Skeletal growth was further accelerated by coinfusion of GRF, but significant depletion of pituitary GH stores suggested that this growth rate may not be sustainable. These experiments confirm the importance of the Tgr rat for investigating the growth promoting potential of the GHSs in the context of GH-deficient dwarfism, and suggest that elevated somatostatin expression may mediate the suppression of the GRF-GH and hypothalamo-pituitary-adrenal axes following continuous GHRP-6 treatment.
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Affiliation(s)
- T Wells
- School of Biosciences, Cardiff University, Museum Avenue, Cardiff CF10 3US, UK.
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29
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Lasko CM, Korytko AI, Wehrenberg WB, Cuttler L. Differential GH-releasing hormone regulation of GHRH receptor mRNA expression in the rat pituitary. Am J Physiol Endocrinol Metab 2001; 280:E626-31. [PMID: 11254470 DOI: 10.1152/ajpendo.2001.280.4.e626] [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: 11/22/2022]
Abstract
To understand the capacity of growth hormone-releasing hormone (GHRH) to regulate expression of the GHRH receptor, we studied the effects of GHRH on GHRH receptor mRNA expression in immature and adult rats by use of pituitary cell culture and immunoneutralization approaches. Pituitary cell cultures from neonatal (2-day-old) and adult (70-day-old) rats were treated with GHRH for 4, 24, or 72 h. The effect of GHRH on GHRH receptor mRNA expression depended on the duration of GHRH exposure in both age groups; short-term (4 h) GHRH treatment significantly reduced GHRH receptor mRNA expression (P < 0.05), whereas intermediate treatment (24 h) restored GHRH receptor mRNA to basal levels, and long-term treatment (72 h) stimulated GHRH receptor mRNA expression (P < 0.02). The long-term stimulatory effect of GHRH on GHRH receptor mRNA expression required the presence of serum in the culture medium, and, in the absence of serum, the stimulatory effect was completely abolished. Moreover, the capacity of the pituitary to increase GHRH receptor mRNA expression in response to 72-h GHRH treatment was age dependent, with neonatal pituitaries exhibiting a much greater stimulatory effect than adult pituitaries (P < 0.025). Immunoneutralization of endogenous GHRH significantly reduced GHRH receptor mRNA expression in neonatal (P < 0.004), juvenile (P < 0.003), and mature (P < 0.004) pituitaries compared with age-matched controls. Taken together, these results indicate that GHRH is a potent regulator of GHRH receptor gene expression in immature and mature pituitaries; however, the nature and direction of GHRH regulation of its receptor depend significantly on several variables, including the duration of GHRH exposure, the presence of permissive components in serum, and the developmental stage of the pituitary.
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Affiliation(s)
- C M Lasko
- Department of Pediatrics, Case Western Reserve University, 11100 Euclid Ave., Cleveland, OH 44106-6004, USA
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30
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Taylor AD, Christian HC, Morris JF, Flower RJ, Buckingham JC. Evidence from immunoneutralization and antisense studies that the inhibitory actions of glucocorticoids on growth hormone release in vitro require annexin 1 (lipocortin 1). Br J Pharmacol 2000; 131:1309-16. [PMID: 11090102 PMCID: PMC1572454 DOI: 10.1038/sj.bjp.0703694] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2000] [Revised: 09/05/2000] [Accepted: 09/06/2000] [Indexed: 11/08/2022] Open
Abstract
1. Our previous studies have identified a role for annexin 1 as a mediator of glucocorticoid action in the neuroendocrine system. The present study centred on growth hormone (GH) and exploited antisense and immunoneutralization strategies to examine in vitro the potential role of annexin 1 in effecting the regulatory actions of glucocorticoids on the secretion of this pituitary hormone. 2. Rat anterior pituitary tissue responded in vitro to growth hormone releasing hormone, forskolin, 8-Bromo-cyclic adenosine 3'5'-monophosphate (8-Br-cyclic AMP) and an L-Ca(2+) channel opener (BAY K8644) with concentration-dependent increases GH release which were readily inhibited by corticosterone and dexamethasone. 3. The inhibitory actions of the steroids on GH release elicited by the above secretagogues were effectively reversed by an annexin 1 antisense oligodeoxynucleotide (ODN), but not by control (sense or scrambled) ODNs, as also were the glucocorticoid-induced increases in annexin 1. Similarly, a specific anti-annexin 1 monoclonal antibody quenched the corticosterone-induced suppression of secretagogue-evoked GH release while an isotype matched control antibody was without effect. 4. Transmission electron micrographs showed that the integrity and ultrastructural morphology of the pituitary cells were well preserved at the end of the incubation and unaffected by exposure to the ODNs, antibodies, steroids or secretagogues. 5. The results provide novel evidence for a role for annexin 1 as a mediator of the inhibitory actions of glucocorticoids on the secretion of GH by the anterior pituitary gland and suggest that its actions are effected at a point distal to the formation of cyclic AMP and Ca(2+) entry.
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Affiliation(s)
- A D Taylor
- Department of Neuroendocrinology, Division of Neuroscience and Psychological Medicine, Imperial College School of Medicine, Charing Cross Hospital, Fulham Palace Road, London, W6 8RF
| | - H C Christian
- Department of Human Anatomy and Genetics, The University of Oxford, South Parks Road, Oxford, OX1 3QX
| | - J F Morris
- Department of Human Anatomy and Genetics, The University of Oxford, South Parks Road, Oxford, OX1 3QX
| | - R J Flower
- Department of Biochemical Pharmacology, The William Harvey Research Institute, St. Bartholomew's and the Royal London School of Medicine at Queen Mary and Westfield College, Charterhouse Square, London, EC1M 6BQ
| | - J C Buckingham
- Department of Neuroendocrinology, Division of Neuroscience and Psychological Medicine, Imperial College School of Medicine, Charing Cross Hospital, Fulham Palace Road, London, W6 8RF
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31
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Nogami H, Matsubara M, Harigaya T, Katayama M, Kawamura K. Retinoic acids and thyroid hormone act synergistically with dexamethasone to increase growth hormone-releasing hormone receptor messenger ribonucleic acid expression. Endocrinology 2000; 141:4396-401. [PMID: 11108247 DOI: 10.1210/endo.141.12.7838] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The effects of all-trans-retinoic acid (RA), 9-cis-retinoic acid (9cRA), and thyroid hormone (T3) on GH-releasing hormone receptor (GHRH-R) messenger RNA (mRNA) expression were studied using ribonuclease protection assay in the fetal rat pituitary gland and in MtT/S cells, a clonal GH cell line derived from an estrogen-induced somatotropic tumor in the rat. Although RA (1 microM), 9cRA (1 microM), or T3 (1 nM) alone showed little effect on GHRH-R mRNA expression in the MtT/S cells, each of these substances was found to act synergistically with dexamethasone (DEX; 500 nM) to increase GHRH-R mRNA expression. The effects of RAs and T3 were dose dependent, with maximum effects observed at 1 microM and 1 nM, respectively. The maximum effect of RAs or T3 was not further augmented by the addition of T3 or RAs, respectively. No apparent differences were observed in this study between the actions of RA and 9cRA. The Northern analyses showed that MtT/S cells express retinoic acid receptor alpha2 mRNA and thyroid hormone receptor beta2 mRNA, and DEX did not affect the levels of these mRNAs. This suggests that the role of DEX in enabling RAs or T3 to up-regulate GHRH-R mRNA levels is not an induction of the expression of each specific receptor for RAs and T3. The similar enhancement of DEX induction of GHRH-R mRNA by RAs or T3 was also observed in the fetal rat pituitary gland in culture, suggesting that RA and/or T3 is involved in the mechanisms responsible for the developmentally regulated expression of GHRH-R mRNA.
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Affiliation(s)
- H Nogami
- Department of Anatomy, Keio University School of Medicine, Tokyo, Japan.
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32
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García-Fernández LF, Iñiguez MA, Eguchi N, Fresno M, Urade Y, Muñoz A. Dexamethasone induces lipocalin-type prostaglandin D synthase gene expression in mouse neuronal cells. J Neurochem 2000; 75:460-70. [PMID: 10899920 DOI: 10.1046/j.1471-4159.2000.0750460.x] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Lipocalin-type prostaglandin (PG) D synthase (L-PGDS) is responsible for the production of PGD(2), the main PG in the CNS. PGD(2) is an endogenous sleep inducer, and it is involved in the control of odor and pain responses and body temperature. In addition, PGD synthase transports lipophilic molecules in the subarachnoid space and CSF. By northern and western assays we show that the synthetic glucocorticoid dexamethasone, an inhibitor of PG production in most tissues, induces L-PGDS mRNA and protein in a dose- and time-dependent fashion in mouse neuronal GT1-7 cells. Accordingly, dexamethasone increases cellular L-PGDS enzymatic activity. Dexamethasone induced L-PGDS gene transcription in run-on assays and activated the mouse L-PGDS gene promoter in transiently transfected cells. It is interesting that the tumor promoter 12-O-tetradecanoyl-phorbol 13-acetate (TPA), which induces the synthesis of PGs in many tissues, inhibited the increase in L-PGDS expression induced by dexamethasone. In contrast, neither dexamethasone nor TPA affected the expression of cyclooxygenases-1 and -2. Our data demonstrate that dexamethasone induces L-PGDS gene transcription in neuronal cells.
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Affiliation(s)
- L F García-Fernández
- Instituto de Investigaciones Biomédicas "Alberto Sols" Consejo Superior de Investigaciones Científicas-Universidad Autónoma de Madrid, Madrid, Spain
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Tamura H, Kamegai J, Sugihara H, Kineman RD, Frohman LA, Wakabayashi I. Glucocorticoids regulate pituitary growth hormone secretagogue receptor gene expression. J Neuroendocrinol 2000; 12:481-5. [PMID: 10844575 DOI: 10.1046/j.1365-2826.2000.00446.x] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Glucocorticoids regulate growth hormone (GH) secretion by modulating both hypothalamic and pituitary function. At the level of the pituitary, glucocorticoids increase GH and GH-releasing hormone receptor (GHRH-R) gene expression. To test if glucocorticoids might also regulate the pituitary expression of the recently identified GH secretagogue (GHS) receptor, GHS-R; adult male rats were adrenalectomized or sham operated, and treated with the synthetic glucocorticoid (dexamethasone, 200 microg/day) or vehicle for 8 days. Pituitary GHS-R mRNA levels were assessed by reverse transcriptase polymerase chain reaction (RT-PCR). Adrenalectomy decreased pituitary GHS-R mRNA to 45% of vehicle-treated, sham-operated rats (P < 0.05). Administration of dexamethasone increased GHS-R mRNA levels in sham-operated as well as in adrenalectomized rats (199 +/- 24% (P < 0.05) and 369 +/- 48% (P < 0.01) of vehicle-treated controls). Addition of dexamethasone to primary rat pituitary cell cultures increased GHS-R mRNA levels in a dose- and time-dependent manner while the transcriptional inhibitor, actinomycin D, completely blocked the stimulatory action of dexamethasone. Taken together, these results suggest glucocorticoids directly increase pituitary GHS-R mRNA levels by stimulating GHS-R gene transcription.
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Affiliation(s)
- H Tamura
- Department of Medicine, Nippon Medical School, Tokyo, Japan
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Kovacs M, Kineman RD, Schally AV, Flerko B, Frohman LA. Increase in mRNA concentrations of pituitary receptors for growth hormone-releasing hormone and growth hormone secretagogues after neonatal monosodium glutamate treatment. J Neuroendocrinol 2000; 12:335-41. [PMID: 10718930 DOI: 10.1046/j.1365-2826.2000.00458.x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Previous studies have demonstrated that neonatal monosodium glutamate (MSG) treatment destroys growth hormone releasing-hormone (GHRH) neurones within the hypothalamic arcuate nucleus, decreases serum GH and insulin-like growth factor (IGF-I) concentrations, and retards linear growth. In the present study we investigated whether expression of pituitary GH, GHRH receptors (GHRH-R), growth hormone secretagogue receptors (GHS-R) and liver IGF-I is altered in this model of GHRH deficiency. In addition, we investigated if treatment of MSG-lesioned rats with the GHRH agonist, JI-38, would 'normalise' the GH-axis. Serum GH and IGF-I concentrations were determined by RIA, GH mRNA levels were evaluated by Northern blotting, and GHRH-R, GHS-R and IGF-I mRNA levels were measured by semiquantitative RT-PCR. In accord with previous reports, neonatal MSG treatment caused 50% and 76% decreases in serum GH and IGF-I concentrations, respectively, at 8 weeks of age. The decline in circulating GH was accompanied by a 56% reduction in total pituitary GH content, which was a reflection of the decrease in total pituitary protein. However, GH concentration (per mg protein) was unaltered. Despite the maintenance of a normal GH concentration, GH mRNA concentration (per microg total RNA) was suppressed by 42%, compared to saline-treated controls (P<0.05). These data indicate that a post-transcriptional mechanism, such as a reduction in the GH secretory rate, acts to maintain intracellular GH concentrations. The fall in circulating concentrations of GH leads to a 42% decrease in liver IGF-IB mRNA levels, while liver IGF-IA transcripts showed only a 27% suppression. In contrast, pituitary GHRH-R and GHS-R mRNA levels (per microg total RNA) were increased in MSG-lesioned rats by 96% and 180% of normal values (P<0.01), respectively. Twice daily treatment of MSG-lesioned rats (for 2 weeks) with the GHRH agonist, JI-38, increased serum GH and IGF-I levels, as measured 20 h after the last agonist injection. However, GH, IGF-I, GHRH-R and GHS-R mRNA levels were not altered at this time. These results demonstrate that intermittent GHRH agonist treatment stimulates pituitary GH secretion and GH in turn stimulates hepatic IGF-I but that effects on gene expression are not sustained. Collectively, our observations demonstrate a complex interplay between transcriptional, translational and post-translational mechanisms within each level of the GH-axis following destruction of GHRH neurones by neonatal MSG treatment.
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Affiliation(s)
- M Kovacs
- Department of Medicine, Tulane University School of Medicine, New Orleans, LA, USA.
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Miller TL, Godfrey PA, Dealmeida VI, Mayo KE. The rat growth hormone-releasing hormone receptor gene: structure, regulation, and generation of receptor isoforms with different signaling properties. Endocrinology 1999; 140:4152-65. [PMID: 10465288 DOI: 10.1210/endo.140.9.6977] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
The interaction of GHRH with membrane-bound receptors on somatotroph cells of the anterior pituitary is an important step in the regulation of GH synthesis and secretion. The identification of a G protein-coupled receptor for GHRH has made it possible to investigate the pathway by which GHRH regulates pituitary somatotroph cell function. To initiate an analysis of the mechanisms regulating expression and function of the GHRH receptor, the structure of the gene and its promoter region were analyzed. The coding sequence of the rat GHRH receptor gene is contained within 14 exons spanning approximately 15 kb of genomic DNA. Four transcription start sites are located within 286 bp upstream of the initiation codon. The 5' flanking region of the GHRH receptor gene acts as a functional promoter in rat pituitary tumor GH3 cells, and basal promoter activity is enhanced in GH3 and COS7 cells by cotransfection of an expression construct encoding the pituitary-specific transcription factor Pit-1. The rat GHRH receptor gene is subject to at least 1 alternative RNA processing event that generates 2 receptor isoforms differing by 41 amino acids within the third intracellular loop (IL) of the protein. The short isoform of the GHRH receptor is predominant in pituitary cells. The MtT/S pituitary tumor cell line was found to express the GHRH receptor, and different populations of these cells produce predominantly the long or short isoforms of the receptor messenger RNA, suggesting that the alternative splicing can be regulated. Functional analysis of the two GHRH receptor isoforms demonstrates that both bind GHRH, but only the short isoform signals through a cAMP-mediated pathway. Neither receptor isoform is able to stimulate calcium mobilization from internal stores after GHRH treatment. Our findings indicate that the pituitary-specific transcription factor Pit-1 is involved in the somatotroph-specific expression of the GHRH receptor gene and that functionally distinct receptor proteins are generated by an alternative RNA processing mechanism.
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Affiliation(s)
- T L Miller
- Department of Biochemistry, Northwestern University, Evanston, Illinois 60208, USA
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36
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Nogami H, Inoue K, Moriya H, Ishida A, Kobayashi S, Hisano S, Katayama M, Kawamura K. Regulation of growth hormone-releasing hormone receptor messenger ribonucleic acid expression by glucocorticoids in MtT-S cells and in the pituitary gland of fetal rats. Endocrinology 1999; 140:2763-70. [PMID: 10342867 DOI: 10.1210/endo.140.6.6787] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Regulation of GH-releasing hormone receptor (GHRH-R) messenger RNA (mRNA) expression was studied, with the ribonuclease protection assay, in the fetal rat pituitary gland and in MtT-S clonal cells. GHRH-R mRNA was first detected on embryonic day (E)19 and increased rapidly thereafter, to reach a maximum at E21. Incubation of E17 or E18 pituitaries with 50 nM dexamethasone (DEX), a synthetic glucocorticoid, induced GHRH-R mRNA expression, suggesting that glucocorticoids play a pivotal role in the developmental expression of this mRNA. In E19 pituitaries, 24 h treatment with DEX increased GHRH-R mRNA by 60%, and GH mRNA by 76%, but did not affect pit-1 mRNA level, suggesting that the effect of DEX is specific for expressions of GH mRNA and GHRH-R mRNA. The accumulation of GHRH-R mRNA by DEX was time dependent, and it was slightly enhanced by the protein synthesis inhibitor, puromycin (100 microM). In MtT-S cells (a pituitary cell line established from an estrogen-induced tumor), DEX induced GHRH-R mRNA expression within 2 h in a dose-dependent manner. This induction was augmented by puromycin (100 microM) or cycloheximide (3.5 microM). However, the RNA synthesis inhibitor Actinomycin D (1 microM) completely inhibited GHRH-R mRNA accumulation in response to either DEX or DEX plus puromycin, suggesting that glucocorticoids induce GHRH-R mRNA mainly through stimulation of mRNA transcription. These results suggest: that GHRH-R mRNA accumulation in the fetal pituitary gland of rats normally occurs at E19, probably because of the direct action of glucocorticoids on the pituitary gland, to stimulate GHRH-R mRNA transcription; and that the expression of glucocorticoid receptors is an important event in GH cell development in rats. Accordingly, immunocytochemical results suggest an increase in glucocorticoid receptors in immature GH cells between E17 and E18. The present results also imply that MtT-S cells may be a good model in which to further study the molecular mechanisms of the regulation of GHRH-R gene expression.
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Affiliation(s)
- H Nogami
- Department of Anatomy, School of Medicine, Keio University, Tokyo, Japan
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37
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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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Petersenn S, Rasch AC, Heyens M, Schulte HM. Structure and regulation of the human growth hormone-releasing hormone receptor gene. Mol Endocrinol 1998; 12:233-47. [PMID: 9482665 DOI: 10.1210/mend.12.2.0057] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
The GHRH receptor (GHRH-R) acts as a critical molecule for proliferation and differentiation of somatotrophic pituitary cells. A role in the pathogenesis of GH hypersecretion and GH deficiency has been implicated. We investigated structure and regulation of the human GHRH-R gene. A genomic clone including approximately 12 kb of 5'-flanking region was isolated. The gene is of complex structure consisting of more than 10 exons. Two kilobase pairs of the promoter were sequenced, and putative transcription factor binding sites were identified. The transcription start site was defined by ribonuclease protection assay. Transcriptional regulation was investigated by transient transfections using promoter fragments ranging in size from 108-1456 bp. GHRH-R promoter (1456 bp) directed high levels of luciferase expression in GH4 rat pituitary cells whereas no activity was detected in JEG3 chorion carcinoma cells or COS-7 monkey kidney cells. A minimal 202-bp promoter allowed pituitary-specific expression. Its activity in COS-7 cells is enhanced by cotransfection of the pituitary-specific transcription factor Pit-1. We did not find any regulation of the GHRH-R promoter by forskolin, phorbol-myristate-acetate, or T3. Glucocorticoids lead to a significant stimulation, and estrogen leads to a significant inhibition. Further mapping suggests a glucocorticoid-responsive element between -1456 and -1181 and an estrogen-responsive element between -202 and -108. These studies demonstrate the complex nature of the human GHRH-R gene and identify its 5'-flanking region. Furthermore, specific activity of the promoter and regulation by various hormones are demonstrated.
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MESH Headings
- Base Sequence
- Cloning, Molecular
- Colforsin/pharmacology
- DNA-Binding Proteins/genetics
- Estrogens/pharmacology
- Gene Expression Regulation/drug effects
- Glucocorticoids/pharmacology
- Humans
- Molecular Sequence Data
- Promoter Regions, Genetic/drug effects
- Receptors, Neuropeptide/biosynthesis
- Receptors, Neuropeptide/chemistry
- Receptors, Neuropeptide/genetics
- Receptors, Pituitary Hormone-Regulating Hormone/biosynthesis
- Receptors, Pituitary Hormone-Regulating Hormone/chemistry
- Receptors, Pituitary Hormone-Regulating Hormone/genetics
- Sequence Analysis, DNA
- Tetradecanoylphorbol Acetate/pharmacology
- Transcription Factor Pit-1
- Transcription Factors/genetics
- Transcription, Genetic
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Affiliation(s)
- S Petersenn
- IHF Institute for Hormone and Fertility Research, University of Hamburg, Germany
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