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Hernández-Ramírez LC, Trivellin G, Stratakis CA. Cyclic 3',5'-adenosine monophosphate (cAMP) signaling in the anterior pituitary gland in health and disease. Mol Cell Endocrinol 2018; 463:72-86. [PMID: 28822849 DOI: 10.1016/j.mce.2017.08.006] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/26/2017] [Revised: 08/11/2017] [Accepted: 08/14/2017] [Indexed: 11/28/2022]
Abstract
The cyclic 3',5'-adenosine monophosphate (cAMP) was the first among the so-called "second messengers" to be described. It is conserved in most organisms and functions as a signal transducer by mediating the intracellular effects of multiple hormones and neurotransmitters. In this review, we first delineate how different members of the cAMP pathway ensure its correct compartmentalization and activity, mediate the terminal intracellular effects, and allow the crosstalk with other signaling pathways. We then focus on the pituitary gland, where cAMP exerts a crucial function by controlling the responsiveness of the cells to hypothalamic hormones, neurotransmitters and peripheral factors. We discuss the most relevant physiological functions mediated by cAMP in the different pituitary cell types, and summarize the defects affecting this pathway that have been reported in the literature. We finally discuss how a deregulated cAMP pathway is involved in the pathogenesis of pituitary disorders and how it affects the response to therapy.
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Affiliation(s)
- Laura C Hernández-Ramírez
- Section on Endocrinology and Genetics, Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD), National Institutes of Health (NIH), 10 Center Drive, CRC, Room 1E-3216, Bethesda, MD 20892-1862, USA
| | - Giampaolo Trivellin
- Section on Endocrinology and Genetics, Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD), National Institutes of Health (NIH), 10 Center Drive, CRC, Room 1E-3216, Bethesda, MD 20892-1862, USA
| | - Constantine A Stratakis
- Section on Endocrinology and Genetics, Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD), National Institutes of Health (NIH), 10 Center Drive, CRC, Room 1E-3216, Bethesda, MD 20892-1862, USA.
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2
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Stamatiades GA, Kaiser UB. Gonadotropin regulation by pulsatile GnRH: Signaling and gene expression. Mol Cell Endocrinol 2018; 463:131-141. [PMID: 29102564 PMCID: PMC5812824 DOI: 10.1016/j.mce.2017.10.015] [Citation(s) in RCA: 113] [Impact Index Per Article: 18.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/01/2017] [Revised: 10/27/2017] [Accepted: 10/27/2017] [Indexed: 12/12/2022]
Abstract
The precise orchestration of hormonal regulation at all levels of the hypothalamic-pituitary-gonadal axis is essential for normal reproductive function and fertility. The pulsatile secretion of hypothalamic gonadotropin-releasing hormone (GnRH) stimulates the synthesis and release of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) by pituitary gonadotropes. GnRH acts by binding to its high affinity seven-transmembrane receptor (GnRHR) on the cell surface of anterior pituitary gonadotropes. Different signaling cascades and transcriptional mechanisms are activated, depending on the variation in GnRH pulse frequency, to stimulate the synthesis and release of FSH and LH. While changes in GnRH pulse frequency may explain some of the differential regulation of FSH and LH, other factors, such as activin, inhibin and sex steroids, also contribute to gonadotropin production. In this review, we focus on the transcriptional regulation of the gonadotropin subunit genes and the signaling pathways activated by pulsatile GnRH.
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Affiliation(s)
- George A Stamatiades
- Division of Endocrinology, Diabetes and Hypertension, Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02115, United States
| | - Ursula B Kaiser
- Division of Endocrinology, Diabetes and Hypertension, Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02115, United States.
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Choi SG, Wang Q, Jia J, Chikina M, Pincas H, Dolios G, Sasaki K, Wang R, Minamino N, Salton SRJ, Sealfon SC. Characterization of Gonadotrope Secretoproteome Identifies Neurosecretory Protein VGF-derived Peptide Suppression of Follicle-stimulating Hormone Gene Expression. J Biol Chem 2016; 291:21322-21334. [PMID: 27466366 DOI: 10.1074/jbc.m116.740365] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2016] [Indexed: 01/21/2023] Open
Abstract
Reproductive function is controlled by the pulsatile release of hypothalamic gonadotropin-releasing hormone (GnRH), which regulates the expression of the gonadotropins luteinizing hormone and FSH in pituitary gonadotropes. Paradoxically, Fshb gene expression is maximally induced at lower frequency GnRH pulses, which provide a very low average concentration of GnRH stimulation. We studied the role of secreted factors in modulating gonadotropin gene expression. Inhibition of secretion specifically disrupted gonadotropin subunit gene regulation but left early gene induction intact. We characterized the gonadotrope secretoproteome and global mRNA expression at baseline and after Gαs knockdown, which has been found to increase Fshb gene expression (1). We identified 1077 secreted proteins or peptides, 19 of which showed mRNA regulation by GnRH or/and Gαs knockdown. Among several novel secreted factors implicated in Fshb gene regulation, we focused on the neurosecretory protein VGF. Vgf mRNA, whose gene has been implicated in fertility (2), exhibited high induction by GnRH and depended on Gαs In contrast with Fshb induction, Vgf induction occurred preferentially at high GnRH pulse frequency. We hypothesized that a VGF-derived peptide might regulate Fshb gene induction. siRNA knockdown or extracellular immunoneutralization of VGF augmented Fshb mRNA induction by GnRH. GnRH stimulated the secretion of the VGF-derived peptide NERP1. NERP1 caused a concentration-dependent decrease in Fshb gene induction. These findings implicate a VGF-derived peptide in selective regulation of the Fshb gene. Our results support the concept that signaling specificity from the cell membrane GnRH receptor to the nuclear Fshb gene involves integration of intracellular signaling and exosignaling regulatory motifs.
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Affiliation(s)
| | - Qian Wang
- From the Departments of Neurology and
| | | | | | | | | | - Kazuki Sasaki
- Department of Molecular Pharmacology, National Cerebral and Cardiovascular Center Research Institute, Osaka 565-8565, Japan
| | | | - Naoto Minamino
- Department of Molecular Pharmacology, National Cerebral and Cardiovascular Center Research Institute, Osaka 565-8565, Japan
| | - Stephen R J Salton
- Fishberg Department of Neuroscience, Icahn School of Medicine at Mount Sinai, New York, New York 10029 and
| | - Stuart C Sealfon
- From the Departments of Neurology and Center for Advanced Research on Diagnostic Assays, and
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Choi SG, Wang Q, Jia J, Pincas H, Turgeon JL, Sealfon SC. Growth differentiation factor 9 (GDF9) forms an incoherent feed-forward loop modulating follicle-stimulating hormone β-subunit (FSHβ) gene expression. J Biol Chem 2014; 289:16164-75. [PMID: 24778184 DOI: 10.1074/jbc.m113.537696] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Gonadotropin-releasing hormone (GnRH) is secreted in brief pulses from the hypothalamus and regulates follicle-stimulating hormone β-subunit (FSHβ) gene expression in pituitary gonadotropes in a frequency-sensitive manner. The mechanisms underlying its preferential and paradoxical induction of FSHβ by low frequency GnRH pulses are incompletely understood. Here, we identify growth differentiation factor 9 (GDF9) as a GnRH-suppressed autocrine inducer of FSHβ gene expression. GDF9 gene transcription and expression were preferentially decreased by high frequency GnRH pulses. GnRH regulation of GDF9 was concentration-dependent and involved ERK and PKA. GDF9 knockdown or immunoneutralization reduced FSHβ mRNA expression. Conversely, exogenous GDF9 induced FSHβ expression in immortalized gonadotropes and in mouse primary pituitary cells. GDF9 exposure increased FSH secretion in rat primary pituitary cells. GDF9 induced Smad2/3 phosphorylation, which was impeded by ALK5 knockdown and by activin receptor-like kinase (ALK) receptor inhibitor SB-505124, which also suppressed FSHβ expression. Smad2/3 knockdown indicated that FSHβ induction by GDF9 involved Smad2 and Smad3. FSHβ mRNA induction by GDF9 and GnRH was synergistic. We hypothesized that GDF9 contributes to a regulatory loop that tunes the GnRH frequency-response characteristics of the FSHβ gene. To test this, we determined the effects of GDF9 knockdown on FSHβ induction at different GnRH pulse frequencies using a parallel perifusion system. Reduction of GDF9 shifted the characteristic pattern of GnRH pulse frequency sensitivity. These results identify GDF9 as contributing to an incoherent feed-forward loop, comprising both intracellular and secreted components, that regulates FSHβ expression in response to activation of cell surface GnRH receptors.
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Affiliation(s)
- Soon Gang Choi
- From the Center for Translational Systems Biology and Department of Neurology, Icahn School of Medicine at Mount Sinai, New York, New York 10029 and
| | - Qian Wang
- From the Center for Translational Systems Biology and Department of Neurology, Icahn School of Medicine at Mount Sinai, New York, New York 10029 and
| | - Jingjing Jia
- From the Center for Translational Systems Biology and Department of Neurology, Icahn School of Medicine at Mount Sinai, New York, New York 10029 and
| | - Hanna Pincas
- From the Center for Translational Systems Biology and Department of Neurology, Icahn School of Medicine at Mount Sinai, New York, New York 10029 and
| | - Judith L Turgeon
- the Division of Endocrinology, Department of Internal Medicine, School of Medicine, University of California, Davis, California 95616
| | - Stuart C Sealfon
- From the Center for Translational Systems Biology and Department of Neurology, Icahn School of Medicine at Mount Sinai, New York, New York 10029 and
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Pincas H, Choi SG, Wang Q, Jia J, Turgeon JL, Sealfon SC. Outside the box signaling: secreted factors modulate GnRH receptor-mediated gonadotropin regulation. Mol Cell Endocrinol 2014; 385:56-61. [PMID: 23994024 PMCID: PMC3964483 DOI: 10.1016/j.mce.2013.08.015] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/02/2013] [Revised: 08/13/2013] [Accepted: 08/19/2013] [Indexed: 12/24/2022]
Abstract
Control of gene expression following activation of membrane receptors results from the regulation of intracellular signaling pathways and transcription factors. Accordingly, research to elucidate the regulatory control circuits and cellular data processing mechanisms focuses on intracellular mechanisms. While autocrine and paracrine signaling are acknowledged in endocrinology, secreted factors are not typically recognized as fundamental components of the pathways connecting cell surface receptors to gene control in the nucleus. Studies of the gonadotrope suggest that extracellular regulatory loops may play a central role in the regulation of gonadotropin gene expression by gonadotropin-releasing hormone (GnRH) receptor activation. We review emerging evidence for this phenomenon, which we refer to as exosignaling, in gonadotropin gene control and in other receptor-mediated signaling systems. We propose that basic signaling circuit modules controlling gene expression can be seamlessly distributed across intracellular and exosignaling components that together orchestrate the precise physiological control of gene expression.
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Affiliation(s)
- Hanna Pincas
- Department of Neurology, Center for Translational Systems Biology, Icahn School of Medicine at Mount Sinai, New York, NY 10029, United States.
| | - Soon Gang Choi
- Department of Neurology, Center for Translational Systems Biology, Icahn School of Medicine at Mount Sinai, New York, NY 10029, United States.
| | - Qian Wang
- Department of Neurology, Center for Translational Systems Biology, Icahn School of Medicine at Mount Sinai, New York, NY 10029, United States.
| | - Jingjing Jia
- Department of Neurology, Center for Translational Systems Biology, Icahn School of Medicine at Mount Sinai, New York, NY 10029, United States.
| | - Judith L Turgeon
- Division of Endocrinology, Department of Internal Medicine, School of Medicine, University of California, Davis, CA 95616, United States.
| | - Stuart C Sealfon
- Department of Neurology, Center for Translational Systems Biology, Icahn School of Medicine at Mount Sinai, New York, NY 10029, United States.
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Abstract
G protein-coupled receptors (GPCRs) are the largest class of integral membrane protein receptors in the human genome. We examined here the reports whether the GnRH receptor (GnRHR) interacts with a single or multiple types of G proteins. It seems that the GnRHR, as other GPCRs, alternates between various conformations and is stabilized by its ligands, other modulators and intracellular partners in selective conformations culminating in coupling with a single type or multiple G proteins in a cell- and context-specific manner.
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Affiliation(s)
- Zvi Naor
- Department of Biochemistry and Molecular Biology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv 69978, Israel.
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Bernard DJ, Fortin J, Wang Y, Lamba P. Mechanisms of FSH synthesis: what we know, what we don't, and why you should care. Fertil Steril 2010; 93:2465-85. [DOI: 10.1016/j.fertnstert.2010.03.034] [Citation(s) in RCA: 88] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2009] [Accepted: 03/11/2010] [Indexed: 12/17/2022]
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Fernández M, Bianchi M, Lux-Lantos V, Libertun C. Neonatal exposure to bisphenol a alters reproductive parameters and gonadotropin releasing hormone signaling in female rats. ENVIRONMENTAL HEALTH PERSPECTIVES 2009; 117:757-62. [PMID: 19479018 PMCID: PMC2685838 DOI: 10.1289/ehp.0800267] [Citation(s) in RCA: 124] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/08/2008] [Accepted: 01/06/2009] [Indexed: 05/03/2023]
Abstract
BACKGROUND Bisphenol A (BPA) is a component of polycarbonate plastics, epoxy resins, and polystyrene and is found in many products. Several reports have revealed potent in vivo effects, because BPA acts as an estrogen agonist and/or antagonist and as an androgen and thyroid hormone antagonist. OBJECTIVES We analyzed the effects of neonatal exposure to BPA on the reproductive axis of female Sprague-Dawley rats. METHODS Female rats were injected subcutaneously, daily, from postnatal day 1 (PND1) to PND10 with BPA [500 microg/50 microL (high) or 50 microg/50 microL (low)] in castor oil or with castor oil vehicle alone. We studied body weight and age at vaginal opening, estrous cycles, and pituitary hormone release in vivo and in vitro, as well as gonadotropin-releasing hormone (GnRH) pulsatility at PND13 and in adults. We also analyzed two GnRH-activated signaling pathways in the adults: inositol-triphosphate (IP(3)), and extracellular signal-regulated kinase(1/2) (ERK(1/2)). RESULTS Exposure to BPA altered pituitary function in infantile rats, lowering basal and GnRH-induced luteinizing hormone (LH) and increasing GnRH pulsatility. BPA dose-dependently accelerated puberty onset and altered estrous cyclicity, with the high dose causing permanent estrus. In adults treated neonatally with BPA, GnRH-induced LH secretion in vivo was decreased and GnRH pulsatility remained disrupted. In vitro, pituitary cells from animals treated with BPA showed lower basal LH and dose-dependently affected GnRH-induced IP(3) formation; the high dose also impaired GnRH-induced LH secretion. Both doses altered ERK(1/2) activation. CONCLUSIONS Neonatal exposure to BPA altered reproductive parameters and hypothalamic-pituitary function in female rats. To our knowledge, these results demonstrate for the first time that neonatal in vivo BPA permanently affects GnRH pulsatility and pituitary GnRH signaling.
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Affiliation(s)
- Marina Fernández
- Instituto de Biología y Medicina Experimental, Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina
- Facultad de Medicina, Universidad de Buenos Aires, Argentina
| | - Maria Bianchi
- Instituto de Biología y Medicina Experimental, Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina
| | - Victoria Lux-Lantos
- Instituto de Biología y Medicina Experimental, Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina
| | - Carlos Libertun
- Instituto de Biología y Medicina Experimental, Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina
- Facultad de Medicina, Universidad de Buenos Aires, Argentina
- Address correspondence to C. Libertun, IByME-CONICET, Vuelta de Obligado 2490, (C1428ADN) Buenos Aires, Argentina. Telephone: 54-11-4783-2869. Fax: 54-11-4786-2564. E-mail:
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9
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Signaling by G-protein-coupled receptor (GPCR): studies on the GnRH receptor. Front Neuroendocrinol 2009; 30:10-29. [PMID: 18708085 DOI: 10.1016/j.yfrne.2008.07.001] [Citation(s) in RCA: 199] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/30/2007] [Revised: 04/28/2008] [Accepted: 07/21/2008] [Indexed: 01/22/2023]
Abstract
Gonadotropin-releasing hormone (GnRH) is the first key hormone of reproduction. GnRH analogs are extensively used in in vitro fertilization, and treatment of sex hormone-dependent cancers, due to their ability to bring about 'chemical castration'. The interaction of GnRH with its cognate type I receptor (GnRHR) in pituitary gonadotropes results in the activation of Gq/G(11), phospholipase Cbeta (PLCbetaI), PLA(2), and PLD. Sequential activation of the phospholipases generates the second messengers inositol 1, 4, 5-trisphosphate (IP(3)), diacylglycerol (DAG), and arachidonic acid (AA), which are required for Ca(2+) mobilization, the activation of various protein kinase C isoforms (PKCs), and the production of prostaglandin (PG) and other metabolites of AA, respectively. PKC isoforms are the major mediators of the downstream activation of a number of mitogen-activated protein kinase (MAPK) cascades by GnRH, namely: extracellular signal-regulated kinase (ERK), jun-N-terminal kinase (JNK), and p38MAPK. The activated MAPKs phosphorylate both cytosolic and nuclear proteins to initiate the transcriptional activation of the gonadotropin subunit genes and the GnRHR. While Ca(2+) mobilization has been found to initiate rapid gonadotropin secretion, Ca(2+), together with various PKC isoforms, MAPKs and AA metabolites also serve as key nodes, in the GnRH-stimulated signaling network that enables the gonadotropes to decode GnRH pulse frequencies and translating that into differential gonadotropin synthesis and release. Even though pulsatility of GnRH is recognized as a major determinant for differential gonadotropin subunit gene expression and gonadotropin secretion very little is yet known about the signaling circuits governing GnRH action at the 'Systems Biology' level. Direct apoptotic and metastatic effects of GnRH analogs in gonadal steroid-dependent cancers expressing the GnRHR also seem to be mediated by the activation of the PKC/MAPK pathways. However, the mechanisms dictating life (pituitary) vs. death (cancer) decisions made by the same GnRHR remain elusive. Understanding these molecular mechanisms triggered by the GnRHR through biochemical and 'Systems Biology' approaches would provide the basis for the construction of the dynamic connectivity maps, which operate in the various cell types (endocrine, cancer, and immune system) targeted by GnRH. The connectivity maps will open a new vista for exploring the direct effects of GnRH analogs in tumors and the design of novel combined therapies for fertility control, reproductive disorders and cancers.
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Shacham S, Cheifetz MN, Fridkin M, Pawson AJ, Millar RP, Naor Z. Identification of Ser153 in ICL2 of the gonadotropin-releasing hormone (GnRH) receptor as a phosphorylation-independent site for inhibition of Gq coupling. J Biol Chem 2005; 280:28981-8. [PMID: 15964850 DOI: 10.1074/jbc.m500312200] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Type I gonadotropin-releasing hormone (GnRH) receptor (GnRHR) is unique among mammalian G-protein-coupled receptors (GPCRs) in lacking a C-terminal tail, which is involved in desensitization in GPCRs. Therefore, we searched for inhibitory sites in the intracellular loops (ICLs) of the GnRHR. Synthetic peptides corresponding to the three ICLs were inserted into permeabilized alphaT3-1 gonadotrope cells, and GnRH-induced inositol phosphate (InsP) formation was determined. GnRH-induced InsP production was potentiated by ICL2 > ICL3 but not by the ICL1 peptides, suggesting they are acting as decoy peptides. We examined the effects of six peptides in which only one of the Ser or Thr residues was substituted with Ala or Glu. Only substitution of Ser153 with Ala or Glu ablated the potentiating effect upon GnRH-induced InsP elevation. ERK activation was enhanced, and the rate of GnRH-induced InsP formation was about 6.5-fold higher in the first 10 min in COS-1 cells that were transfected with mutants of the GnRHR in which the ICL2 Ser/Thr residues (Ser151, Ser153, and Thr142) or only Ser153 was mutated to Ala as compared with the wild type GnRHR. The data indicate that ICL2 harbors an inhibitory domain, such that exogenous ICL2 peptide serves as a decoy for the inhibitory site (Ser153) of the GnRHR, thus enabling further activation. GnRH does not induce receptor phosphorylation in alphaT3-1 cells. Because the phosphomimetic ICL2-S153E peptide did not mimic the stimulatory effect of the ICL2 peptide, the inhibitory effect of Ser153 operates through a phosphorylation-independent mechanism.
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Affiliation(s)
- Sharon Shacham
- Department of Biochemistry, George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv 69978, Israel
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Blitek A, Ziecik A, Gajewska A, Kodaka M, Counis R, Kochman K. Cobalt complex with GnRH stimulates the LH release and PKA signaling pathway in pig anterior pituitary cells in vitro. Brain Res Bull 2005; 65:391-6. [PMID: 15833593 DOI: 10.1016/j.brainresbull.2005.02.008] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2005] [Accepted: 02/03/2005] [Indexed: 11/18/2022]
Abstract
Metal complexes with GnRH were shown to interact with GnRH receptors in pituitary cells. In the present study we examined the effects of GnRH and its cobalt complex form (Co-GnRH) on LH secretion and generation of second messengers, namely inositol phosphates (IPs) and cAMP, in porcine pituitary cells in vitro. The cells were obtained from gilt pituitary at the pre-ovulatory phase of estrous cycle and cultured for 72 h before challenge with GnRH or Co-GnRH. Both substances induced a significant increase in LH release that was detectable after 60 min (P<0.05) of treatment, with the Co-GnRH complex being more efficient than GnRH at 180 min (P<0.01). GnRH and Co-GnRH were equally effective at 10(-8)M (P<0.01), however, at the lowest (10(-9)M) as well as the highest (10(-7)M) concentrations tested, Co-GnRH was more potent than its native counterpart (P<0.01). Interestingly, Co-GnRH revealed twice more efficient than GnRH at stimulating cAMP production, an effect which was detectable in cells after 1h-incubation (P<0.001). In contrast, while native GnRH induced a rapid increase (P<0.05) in IPs no such effect of Co-GnRH was observed. These data demonstrate that Co-GnRH and GnRH differentially effect on the signaling pathway in porcine gonadotropes and suggest that in these cells, the releasing action of Co-GnRH results from the mediation via the cAMP/protein kinase A second messenger system.
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Affiliation(s)
- Agnieszka Blitek
- Institute of Animal Reproduction and Food Research, Polish Academy of Sciences, 10-747 Olsztyn, Poland
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Lewy H, Ashkenazi IE, Naor Z. Gonadotropin releasing hormone (GnRH) and estradiol (E(2)) regulation of cell cycle in gonadotrophs. Mol Cell Endocrinol 2003; 203:25-32. [PMID: 12782400 DOI: 10.1016/s0303-7207(03)00119-9] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The number of pituitary cells, their size, hormonal content and release and response to external cues varies between day and night and during the estrus cycle. Previous studies have demonstrated that pituitary cells proliferate rhythmically and that estradiol (E(2)) is a mitogen of alpha T3 cells. We, therefore, studied the effect of gonadotropin releasing hormone (GnRH) and E(2), on the cell cycle in primary cultures of mouse pituitary cells and in the gonadotroph cell line L beta T2. We found that GnRH and E(2) modulate the cell cycle in a time dependent manner and induce proliferation in cultures of mouse pituitary and L beta T2 cells. GnRH induces proliferation in cells isolated in the morning of the estrus day and increases the number of cells in G2 stage when isolated in noon and evening. However, the transition into the G1 stage is enabled only by co-addition of E(2) and GnRH. GnRH stimulates LH release from L beta T2 cells after 2 days via exocytosis while after 4 days in culture, the increase in LH release may be accounted for by the increase in cell number. E(2) enhanced the GnRH response after 2 days, and abolished it after 4 days in culture. Furthermore, E(2) has no effect on LH release and cell number after 2 days in culture, however, after 4 days in culture, E(2) had no effect on the total amount of LH released but inhibited LH release per cell due to increase in cell number. Our results show that GnRH and E(2) function to shorten the cell cycle and regulate the cell number of each stage of the cell cycle. The effect of GnRH and E(2) on the cell cycle is dependent on the circadian time. This mechanism may serve to modulate the size and function of the pituitary cell population and consequently the function of pituitary gonadotrophs regulating the surge of LH release before ovulation.
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Affiliation(s)
- Hadas Lewy
- Unit of Chronobiology, Department of Human Genetics and Molecular Medicine, Sackler School of Medicine, Tel Aviv University, Tel Aviv 69978, Israel.
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Shacham S, Harris D, Ben-Shlomo H, Cohen I, Bonfil D, Przedecki F, Lewy H, Ashkenazi IE, Seger R, Naor Z. Mechanism of GnRH receptor signaling on gonadotropin release and gene expression in pituitary gonadotrophs. VITAMINS AND HORMONES 2001; 63:63-90. [PMID: 11358118 DOI: 10.1016/s0083-6729(01)63003-6] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/16/2023]
Abstract
Gonadotropin releasing hormone (GnRH), the first key hormone of reproduction, is synthesized and secreted from the hypothalamus in a pulsatile manner and stimulates pituitary gonadotrophs (5-10% of the pituitary cells) to synthesize and release gonadotropin luteinizing hormone (LH) and follicle stimulating hormone (FSH). Gonadotrophs consist of 60% multihormonal cells (LH+FSH) and 18% LH- and 22% FSH-containing cells. LH and FSH, members of the glycoprotein hormone family, stimulate spermatogenesis, folliculogenesis, and ovulation. Although GnRH plays a pivotal role in gonadotropin synthesis and release, other factors such as gonadal steroids and gonadal peptides exert positive and negative feedback mechanisms, which affect GnRH actions. GnRH actions include activation of phosphoinositide turnover as well as phospholipase D and A2, mobilization and influx of Ca2+, activation of protein kinase C (PKC) and mitogen-activated protein kinase (MAPK). A complex crosstalk between the above messenger molecules mediates the diverse actions of GnRH. Understanding the signaling mechanisms involved in GnRH actions is the basis for our understanding of basic reproductive functions in general and gonadotropin synthesis and release in particular.
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Affiliation(s)
- S Shacham
- Department of Biochemistry, George S. Wise Faculty of Life Sciences, Sackler Faculty of Medicine, Tel Aviv University, Ramat Aviv, Israel
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Lewy H, Naor Z, Ashkenazi IE. From ultradian to infradian rhythms: LH release patterns in vitro. Chronobiol Int 1999; 16:441-50. [PMID: 10442238 DOI: 10.3109/07420529908998719] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
In the present study, we examined in vitro luteinizing hormone (LH) release patterns from pituitaries and from pituitary cell cultures (3 and 7 days in culture) to elucidate the endogenous period generated by the gonadotroph cell population and to evaluate the relationship between the basic period generated at the cellular level and the output pattern observed at the organ level. In addition, we examined the effect of photic environmental signals perceived by the animals on LH release patterns from pituitaries in vitro. When the animals were exposed to circadian photoperiodic signals, the in vitro LH release pattern from the pituitaries exhibited ultradian, circadian, and infradian frequencies. When the animals were exposed to continuous illumination, the in vitro patterns exhibited only ultradian and infradian frequencies. Furthermore, free running is a process, not a state. This process is driven by a change in the relative dominance of different frequencies that construct the pattern without changing the basic period length. Evaluation of the relative dominance of the different frequencies that construct the pattern indicates that, although infradian oscillators may take part in shaping the output pattern, the basic rhythm generated by the pituitary cells is in the ultradian domain. The results obtained from the examined system suggest that an endogenous oscillator is a cellular entity with ultradian periodicity, and that the rhythmic output of many biological variables is structured by various ultradian components that construct the circadian and infradian output rhythms.
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Affiliation(s)
- H Lewy
- Department of Human Genetics and Molecular Medicine, Sackler School of Medicine, Tel Aviv University, Israel
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15
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Gobbetti A, Zerani M. In vitro nitric oxide effects on basal and gonadotropin-releasing hormone-induced gonadotropin secretion by pituitary gland of male crested newt (Triturus carnifex) during the annual reproductive cycle. Biol Reprod 1999; 60:1217-23. [PMID: 10208987 DOI: 10.1095/biolreprod60.5.1217] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/01/2022] Open
Abstract
The objective of this study was to test the possible nitric oxide (NO) involvement in pituitary gonadotropin secretion in the male crested newt, Triturus carnifex. Pituitaries were incubated in vitro with medium alone, GnRH, NO donor (NOd, sodium nitroprusside), NO synthase inhibitor (NOSi, Nomega-nitro-L-arginine methyl ester), cGMP analogue (cGMPa, 8-bromo-cGMP), soluble guanylate cyclase inhibitor (sGCi, cystamine), GnRH plus NOSi, GnRH plus sGCi, and NOd plus sGCi during the annual reproductive cycle: pre-reproduction, reproduction (noncourtship and courtship), and the refractory, recovery, and estivation periods. To determine pituitary gonadotropin secretion indirectly, newt testes were superfused in vitro with preincubated pituitaries, and androgen release was determined. NO synthase (NOS) activity and cGMP levels were assessed in the preincubated pituitaries. Medium alone- and GnRH-preincubated pituitary increased androgen secretion during pre-reproduction, noncourtship, courtship, and recovery; the GnRH-induced increase was higher than the medium alone-induced increase during pre-reproduction, noncourtship, and recovery. NOd and cGMPa increased androgens in all reproductive phases considered except courtship; the NOd- and cGMP-induced increase was higher than the medium alone-induced increase during pre-reproduction, noncourtship, and recovery. NOS activity was highest during courtship and lowest during the refractory and estivation periods. GnRH increased NOS activity during pre-reproduction, noncourtship, and recovery. Cyclic GMP levels were highest during courtship and lowest during the refractory period and estivation. GnRH increased cGMP levels during pre-reproduction, noncourtship, and recovery, while NOd did so during all reproductive phases considered. These results suggest that basal and GnRH-induced gonadotropin secretion are up-regulated by NO in the pituitary gland of the male Triturus carnifex.
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Affiliation(s)
- A Gobbetti
- Department of Molecular, Cellular, and Animal Biology, University of Camerino, 62032 Camerino, Italy.
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16
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Rajeshwari K, Karande AA. Molecular mimicry by antiidiotypic monoclonal antibody to gonadotropin releasing hormone. Immunol Invest 1999; 28:103-14. [PMID: 10484676 DOI: 10.3109/08820139909061140] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Antipeptide and antiidiotypic antibodies to several receptors are known to mimic their respective ligands in transducing signals on binding their receptors. In our attempts to study gonadotropin releasing hormone receptor, antipeptide and antiidiotypic monoclonal antibodies specific to the receptor were established earlier. The antipeptide mAb F1G4 was to a synthetic peptide corresponding to the extracellular domain of human GnRH receptor and the antiidiotypic mAb 4D10C1 was to the idiotype of a GnRH specific mAb. Here we report the physiological effects of the two mAbs on binding the receptor, as investigated using in vitro cultures of (a) human term placental villi and (b) rat pituitaries. The mAb 4D10C1 exerted a dose-dependent release of human chorionic gonadotropin in cultures of human term placental villi as well as luteinising and follicle stimulating hormones in cultures of rat pituitaries.
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Affiliation(s)
- K Rajeshwari
- Department of Biochemistry, Indian Institute of Science, Bangalore
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17
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Abstract
We studied the possible role of nitric oxide (NO) in GnRH-induced gonadotropin secretion in the female water frog, Rana esculenta. During pre-reproduction, pre-ovulation, ovulation, post-ovulation, refractory, recovery and hibernation, pituitaries were incubated with medium-alone, GnRH, NO donor (NOd), NO synthase inhibitor (NOSi), cyclic GMP analogue (cGMPa), soluble guanylate cyclase inhibitor (sGCi), GnRH plus NOSi, GnRH plus sGCi, and NOd plus sGCi. Because antisera raised against gonadotropins are not available for this species, we measured these hormones indirectly through their effects on ovarian progesterone secretion. The ovaries were superfused with the pituitaries pre-incubated as reported above. In addition, NOS activity and cGMP levels were determined in the pre-incubated pituitaries. Those pre-incubated with medium-alone and with GnRH increased progesterone secretion during pre-reproduction, pre-ovulation, ovulation and recovery; the increase induced by GnRH was higher than that induced by medium-alone during pre-reproduction, pre-ovulation and recovery. NOd and cGMPa increased progesterone in all considered reproductive phases except ovulation; the increase induced by NOd and cGMP was higher than that induced by medium-alone during pre-reproduction, pre-ovulation and recovery. NOS activity was highest during ovulation and lowest during post-ovulation, refractory and hibernation. GnRH increased NOS activity during pre-reproduction, pre-ovulation and recovery. Cyclic GMP levels were highest during ovulation and lowest during post-ovulation, refractory and hibernation. GnRH increased cGMP levels during pre-reproduction, pre-ovulation and recovery, NOd during all considered reproductive phases. These results suggest that NO mediates basal and GnRH-induced gonadotropin secretion in female Rana esculenta.
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Affiliation(s)
- A Gobbetti
- Department of Molecular, Cellular and Animal Biology, University of Camerino, Italy
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18
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Naor Z, Harris D, Shacham S. Mechanism of GnRH receptor signaling: combinatorial cross-talk of Ca2+ and protein kinase C. Front Neuroendocrinol 1998; 19:1-19. [PMID: 9465287 DOI: 10.1006/frne.1997.0162] [Citation(s) in RCA: 93] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Gonadotropin-releasing hormone (GnRH), the first key hormone of reproduction, is synthesized in the hypothalamus and is released in a pulsatile manner to stimulate pituitary gonadotrope-luteinizing hormone (LH) and follicle-stimulating hormone (FSH) synthesis and release. Gonadotropes represent only about 10% of pituitary cells and are divided into monohormonal cells (18% LH and 22% FSH cells) and 60% multihormonal (LH + FSH) cells. GnRH binds to a specific seven transmembrane domain receptor which is coupled to Gq and activates sequentially different phospholipases to provide Ca2+ and lipid-derived messenger molecules. Initially, phospholipase C is activated, followed by activation of both phospholipase A2 (PLA2) and phospholipase D (PLD). Generation of the second messengers inositol 1,4,5-trisphosphate and diacylglycerol (DAG) lead to mobilization of intracellular pools of Ca2+ and activation of protein kinase C (PKC). Early DAG and Ca2+, derived via enhanced phosphoinositide turnover, might be involved in rapid activation of selective Ca(2+)-dependent, conventional PKC isoforms (cPKC). On the other hand, late DAG, derived from phosphatidic acid (PA) via PLD, may activate Ca(2+)-independent novel PKC isoforms (nPKC). In addition, arachidonic acid (AA) which is liberated by activated PLA2, might also support selective activation of PKC isoforms (PKCs) with or without other cofactors. Differential cross-talk of Ca2+, AA, and selective PKCs might generate a compartmentalized signal transduction cascade to downstream elements which are activated during the neurohormone action. Among those elements is the mitogen-activated protein kinase (MAPK) cascade which is activated by GnRH in a PKC-, Ca(2+)-, and protein tyrosine kinase (PTK)-dependent fashion. Transcriptional regulation can be mediated by the activation of transcription factors such as c-fos by MAPK. Indeed, GnRH activates the expression of both c-jun and c-fos which might participate in gene regulation via the formation of AP-1. The signaling cascade leading to gonadotropin (LH and FSH) gene regulation by GnRH is still not known and might involve the above-mentioned cascades. AA and selective lipoxygenase products such as leukotriene C4 also participate in GnRH action, possibly by cross-talk with PKCs, or by an autocrine/paracrine amplification cycle. A complex combinatorial, spatial and temporal cross-talk of the above messenger molecules seems to mediate the diverse effects elicited by GnRH, the first key hormone of the reproductive cycle.
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Affiliation(s)
- Z Naor
- Department of Biochemistry, George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv, Israel.
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19
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Reiss N, Llevi LN, Shacham S, Harris D, Seger R, Naor Z. Mechanism of mitogen-activated protein kinase activation by gonadotropin-releasing hormone in the pituitary of alphaT3-1 cell line: differential roles of calcium and protein kinase C. Endocrinology 1997; 138:1673-82. [PMID: 9075730 DOI: 10.1210/endo.138.4.5057] [Citation(s) in RCA: 82] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
The mechanism of mitogen-activated protein kinase (MAPK, ERK) stimulation by the GnRH analog [D-Trp6]GnRH (GnRH-a) was investigated in the gonadotroph-derived alphaT3-1 cell line. GnRH-a as well as the protein kinase C (PKC) activator 12-O-tetradecanoyl phorbol-13-acetate (TPA) stimulated a sustained response of MAPK activity, whereas epidermal growth factor (EGF) stimulated a transient response. MAPK kinase (MEK) is also activated by GnRH-a, but in a transient manner. GnRH-a and TPA apparently activated mainly the MAPK isoform ERK1, as revealed by Mono-Q fast protein liquid chromatography followed by Western blotting as well as by gel kinase assay. GnRH-a and TPA stimulated the tyrosine phosphorylation of several proteins, and this effect as well as the stimulation of MAPK activity were inhibited by the PKC inhibitor GF 109203X. Similarly, down-regulation of TPA-sensitive PKC subspecies nearly abolished the effect of GnRH-a and TPA on MAPK activity. Furthermore, the protein tyrosine kinase (PTK) inhibitor genistein inhibited protein tyrosine phosphorylation and reduced GnRH-a-stimulated MAPK activity by 50%, suggesting the participation of genistein-sensitive and insensitive pathways in GnRH-a action. Although Ca2+ ionophores have only a marginal stimulatory effect, the removal of Ca2+ markedly reduced MAPK activation by GnRH-a and TPA, but had no effect on GnRH-a and TPA stimulation of protein tyrosine phosphorylation. Interestingly, the removal of Ca2+ also partly inhibited the activation of MAPK by EGF and vanadate/H2O2. Thus, a calcium-dependent component(s) downstream of PKC and PTK might also participate in MAPK activation. Elevation of cAMP by forskolin exerted partial inhibition on EGF, but not on TPA or GnRH-a action, suggesting that MEK activators other than Raf-1 might be involved in GnRH action. We conclude that Ca2+, PTK, and PKC participate in the activation of MAPK by GnRH-a, with Ca2+ being necessary downstream to PKC and PTK.
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Affiliation(s)
- N Reiss
- Department of Biochemistry, George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv, Israel
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20
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Naor Z, Shacham S, Harris D, Seger R, Reiss N. Signal transduction of the gonadotropin releasing hormone (GnRH) receptor: cross-talk of calcium, protein kinase C (PKC), and arachidonic acid. Cell Mol Neurobiol 1995; 15:527-44. [PMID: 8719039 DOI: 10.1007/bf02071315] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
1. The decapeptide neurohormone gonadotropin releasing hormone (GnRH) is the first key hormone of the reproductive system. Produced in the hypothalamus, GnRH is released in a pulsatile manner into the hypophysial portal system to reach the anterior pituitary and stimulates the release and synthesis of the gonadotropin hormones LH and FSH. GnRH, a Ca2+ mobilizing ligand, binds to its respective binding protein, which is a member of the seven transmembrane domain receptor family and activates a G-protein (Gq). 2. The alpha subunit of Gq triggers enhanced phosphoinositide turnover and the elevation of multiple second messengers required for gonadotropin release and biosynthesis. 3. The messenger molecules IP3, diacylglycerol, Ca2+, protein kinase C, arachidonic acid and leukotriene C4 cross-talk in a complex networks of signaling, culminating in gonadotropin release and gene expression.
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Affiliation(s)
- Z Naor
- Department of Biochemistry, Tel Aviv University, Ramat Aviv, Israel
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21
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Stojilkovic SS, Catt KJ. Novel aspects of GnRH-induced intracellular signaling and secretion in pituitary gonadotrophs. J Neuroendocrinol 1995; 7:739-57. [PMID: 8563717 DOI: 10.1111/j.1365-2826.1995.tb00711.x] [Citation(s) in RCA: 68] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Affiliation(s)
- S S Stojilkovic
- Endocrinology and Reproduction Research Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA
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22
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Ortmann O, Bakhit M, Bloh P, Schulz KD, Emons G. Ovarian steroids modulate gonadotropin-releasing hormone-induced biphasic luteinizing hormone secretory responses and inositol phosphate accumulation in rat anterior pituitary cells and alpha T3-1 gonadotrophs. J Steroid Biochem Mol Biol 1995; 54:101-9. [PMID: 7662583 DOI: 10.1016/0960-0760(95)00121-f] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The ovarian steroids estradiol and progesterone act as important modulators of GnRH-induced luteinizing hormone (LH) secretion from anterior pituitary cells. Recently, we demonstrated that the steroids are able to influence GnRH-stimulated Ca2+ mobilization from extra- and intracellular sources. Here we investigated the actions of estradiol and progesterone on GnRH-induced biphasic LH secretory responses in the model of perifused female rat pituitary cells. A 20 min GnRH stimulus elicited biphasic LH responses composed of an initial peak followed by a prolonged plateau phase. Both phases were equally enhanced by long-term (48 h) estradiol treatment. This action was facilitated by subsequent short-term progesterone treatment. In contrast, combined treatment with estradiol and progesterone for 48 h led to inhibited LH secretory profiles. To determine the steroid actions on the extracellular Ca2+ independent component of LH secretion we performed experiments using cells that were perifused with Ca2+ deficient medium. Under these conditions the cells responded exclusively with a single peak phase of LH secretion, which was augmented or inhibited by estradiol and progesterone treatment as described above. To test the hypothesis that an effect of estradiol and progesterone on GnRH-induced polyphophoinositide hydrolysis is responsible for their modulatory actions on Ca2+ signals and LH secretion we measured inositol phosphate (IP) accumulation after different steroid treatment paradigms in rat pituitary cells and alpha T3-1 immortalized gonadotrophs. GnRH-induced IP production was enhanced by long-term estradiol treatment. Short-term exposure of estradiol-primed cells to progesterone did not lead to significant changes of IP production. The long-term progesterone treatment paradigm enhanced GnRH-induced IP formation, while it decreased Ca2+ signals and LH secretion. Alpha T3-1 cells were used to perform more detailed analysis of IP formation. The actions of estradiol and progesterone on the production of inositol mono-, bis-, and trisphosphates were similar to those observed in the mixed cell population. It is concluded that estradiol and progesterone modulate both peak and plateau phases of GnRH-stimulated LH secretory responses, effects which are associated with their impact on Ca2+ signals. Our findings argue against a role of IP modulation in the mechanism of progesterone actions on Ca2+ signaling and LH secretion in gonadotrophs. Such a mechanism might be involved in the positive effects of estradiol in these cells.
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Affiliation(s)
- O Ortmann
- Department of Obstetrics and Gynecology, Philipps University, Marburg, Germany
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23
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Gobbetti A, Zerani M. A novel neuropeptide cellular mechanism in amphibian interrenal steroidogenesis. Cell Signal 1995; 7:269-75. [PMID: 7544992 DOI: 10.1016/0898-6568(94)00085-p] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Interrenals of female Rana esculenta were incubated with gonadotropin-releasing hormone (GnRH), 9-ketoreductase inhibitor (palmitic acid), acetyl salicyclic acid, prostaglandin F2 alpha (PGF2 alpha), forskolin, isobutylmethyl xanthine (IBMX), dibutyril cyclic adenosine monophosphate (dbcAMP). Prostaglandin E2 (PGE2), PGF2 alpha, testosterone and 17 beta-estradiol were assessed on the incubation media. In addition, in the same interrenals, 9-ketoreductase and aromatase activities were evaluated. GnRH increased PGF2 alpha, 17 beta-estradiol, 9-ketoreductase and aromatase, and decreased PGE2 and testosterone. PGF2 alpha increased 17 beta-estradiol and aromatase, and decreased testosterone. Palmitic acid counteracted GnRH effects, while forskolin, IBMX and dbcAMP showed the same PGF2 alpha effects. These results suggest that GnRH stimulates 9-ketoreductase enhancing PGF2 alpha which in turn activates aromatase through cAMP mediation in the interrenal of Rana esculenta.
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Affiliation(s)
- A Gobbetti
- Department of Molecular, Cellular and Animal Biology, University of Camerino, Italy
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24
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Conn PM, Janovick JA, Stanislaus D, Kuphal D, Jennes L. Molecular and cellular bases of gonadotropin-releasing hormone action in the pituitary and central nervous system. VITAMINS AND HORMONES 1995; 50:151-214. [PMID: 7709600 DOI: 10.1016/s0083-6729(08)60656-1] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Affiliation(s)
- P M Conn
- Oregon Regional Primate Research Center, Beaverton 97006
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25
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Stojilkovic SS, Catt KJ. Expression and signal transduction pathways of gonadotropin-releasing hormone receptors. RECENT PROGRESS IN HORMONE RESEARCH 1995; 50:161-205. [PMID: 7740156 DOI: 10.1016/b978-0-12-571150-0.50012-3] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Affiliation(s)
- S S Stojilkovic
- Endocrinology and Reproduction Research Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA
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26
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Activation of protein kinase C beta gene expression by gonadotropin-releasing hormone in alpha T3-1 cell line. Role of Ca2+ and autoregulation by protein kinase C. J Biol Chem 1994. [DOI: 10.1016/s0021-9258(18)47385-1] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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27
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Rawlings S, Demaurex N, Schlegel W. Pituitary adenylate cyclase-activating polypeptide increases [Ca2]i in rat gonadotrophs through an inositol trisphosphate-dependent mechanism. J Biol Chem 1994. [DOI: 10.1016/s0021-9258(17)37514-2] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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28
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Gobbetti A, Zerani M. Mammalian gonadotropin-releasing hormone increases PGF2 alpha production activating diacylglycerol lipase in Rana esculenta interrenal. Cell Signal 1993; 5:63-7. [PMID: 8452754 DOI: 10.1016/0898-6568(93)90008-a] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
The aim of the present paper was to clarify if the prostaglandin F2 alpha (PGF2 alpha) production stimulated by mammalian gonadotropin-releasing hormone (mGnRH) comes from arachidonic acid (AA) freed by diacylglycerol (DAG) and/or membrane phospholipids in the interrenal of Rana esculenta. Interrenals of Rana esculenta were incubated with inhibitors of phospholipase A1 (PLA1), phospholipase A2 (PLA2), phospholipase C (PLC), protein kinase C (PKC) and diacylglycerol lipase (DAGlipase) in the presence or absence of mGnRH. In parallel, the same experiments were carried out using [3H]AA-labelled interrenals. The results of the experiments with non-labelled and [3H]AA-labelled interrenals were in agreement. PLA1, PLA2, PLC, PKC and DAGlipase inhibitors induced a decrease in PGF2 alpha production in interrenals without mGnRH, and PLA2 inhibitor was more effective than other inhibitors. PLC and DAGlipase inhibitors decreased the PGF2 alpha production by interrenals incubated with mGnRH, and PLC inhibitor was more effective than DAGlipase inhibitor. These findings suggest that the main source of AA used for mGnRH-induced PGF2 alpha synthesis is DAG; probably this decapeptide increases PGF2 alpha production enhancing the DAGlipase activity.
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Affiliation(s)
- A Gobbetti
- Department of Molecular, Cellular, and Animal Biology, University of Camerino, Italy
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29
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Ben-Menahem D, Shraga Z, Lewy H, Limor R, Hammel I, Stein R, Naor Z. Dissociation between release and gene expression of gonadotropin alpha-subunit in gonadotropin-releasing hormone-stimulated alpha T3-1 cell line. Biochemistry 1992; 31:12893-8. [PMID: 1281429 DOI: 10.1021/bi00166a026] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
The alpha T3-1 cell line which was derived by targeted tumorigenesis in transgenic mice [Windle et al. (1990) Mol. Endocrinol. 4, 597-603] possesses high-affinity binding sites for GnRH analogs coupled to enhanced phosphoinositide turnover and phospholipase D activity. Incubation of alpha T3-1 cells with [D-Trp6]-GnRH analog (GnRH-A) resulted in a rapid increase in gonadotropin alpha-subunit mRNA levels which was detected already at 30 min of incubation (0.1 nM GnRH-A, 3-fold, p < 0.01). The effect diminished with time to reach basal levels at about 12 h of incubation, with a secondary rise in alpha mRNA levels between 12 and 24 h of incubation. Addition of the protein kinase C activator 12-O-tetradecanoylphorbol 13-acetate (TPA, 100 ng/mL) or the Ca2+ ionophore ionomycin (1 microM) to alpha T3-1 cells also resulted in a rapid increase in alpha-subunit mRNA levels. Surprisingly, GnRH-induced alpha-subunit release was detected only after a lag of 4 h of incubation. Thus, dissociation between exocytosis and gene expression can be demonstrated in GnRH-stimulated alpha T3-1 cell line.
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Affiliation(s)
- D Ben-Menahem
- Department of Biochemistry, George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv, Israel
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30
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Eidne KA, Sellar RE, Couper G, Anderson L, Taylor PL. Molecular cloning and characterisation of the rat pituitary gonadotropin-releasing hormone (GnRH) receptor. Mol Cell Endocrinol 1992; 90:R5-9. [PMID: 1338727 DOI: 10.1016/0303-7207(92)90116-n] [Citation(s) in RCA: 93] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
We have isolated the gonadotropin-releasing hormone receptor (GnRH-R) from a rat anterior pituitary cDNA library, determined its sequence and demonstrated receptor function. The 2.2 kb rat GnRH-R clone encodes a protein of 327 amino acids. A 1.3 kb clone encoding the mouse GnRH-R has previously been described (Tsutsumi et al., 1992). Although both the mouse and rat protein share significant homology with molecules belonging to the family of G protein-coupled receptors, they have certain unusual features, an example being the complete absence of a COOH terminal tail. The 3'-untranslated region reported missing in the mouse is present in the rat cDNA, where an extended 1 kb of 3'-untranslated region extending to the poly-A tail is shown. At the amino acid level, the rat GnRH-R shows considerable homology with that of the mouse. Electrophysiological studies with Xenopus oocytes and transfection of the cDNA into COS-1 cells, have shown that the 2.2 kb cDNA clone encodes a functional receptor.
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Affiliation(s)
- K A Eidne
- MRC Reproductive Biology Unit, Centre for Reproductive Biology, Edinburgh, UK
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31
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Lewy H, Galron R, Bdolah A, Sokolovsky M, Naor Z. Paradoxical signal transduction mechanism of endothelins and sarafotoxins in cultured pituitary cells: stimulation of phosphoinositide turnover and inhibition of prolactin release. Mol Cell Endocrinol 1992; 89:1-9. [PMID: 1338719 DOI: 10.1016/0303-7207(92)90204-j] [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: 12/26/2022]
Abstract
Endothelins (ET-1, ET-2, ET-3 and vasoactive intestinal contractor, VIC) and sarafotoxins (SRTX-b and SRTX-c) appear to bind with high affinity to a homogeneous class of binding sites in cultured rat pituitary cells. All of these ligands seem to interact with the same receptor (ETA-R), except for SRTX-c which apparently binds to a separate receptor. Binding was followed by phosphodiesteric cleavage of phosphoinositides, resulting in the formation of inositol phosphates. No consistent effect on basal or gonadotropin-releasing hormone (GnRH)-induced release of luteinizing hormone (LH) was exerted by ET or SRTX during 2 h of static incubation. On the other hand, both groups of vasoactive peptides inhibited basal and thyrotropin-releasing hormone (TRH)-induced prolactin secretion. Surprisingly, activation of phosphoinositide turnover by TRH in pituitary mammotrophs led to stimulation of prolactin secretion, whereas activation of the same pathway by ET or SRTX resulted in inhibition of prolactin secretion. ET and SRTX stimulated inositol phosphate formation in GH3 cell line and in the gonadotroph-like cell line alpha T-3 (which is capable of producing the alpha subunit of the gonadotrophins), indicating that the peptides interact with both pituitary mammotrophs and gonadotrophs. The very low concentrations (nM range) needed to stimulate phosphoinositide turnover and to inhibit prolactin secretion, as well as the recent finding that ETs are present in the hypothalamo-pituitary axis suggest that ET might participate in the neuroendocrine modulation of pituitary functions. One such possibility is that ETs might be members of the prolactin inhibiting factors (PIFs) family.
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Affiliation(s)
- H Lewy
- Department of Biochemistry, George S. Wise Faculty of Life Sciences, Tel Aviv University, Israel
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Gobbetti A, Zerani M. Mammalian GnRH involvement in prostaglandin F2 alpha and sex steroid hormones testicular release in two amphibian species: the anuran water frog, Rana esculenta, and the urodele crested newt, Triturus carnifex. Gen Comp Endocrinol 1992; 87:240-8. [PMID: 1398018 DOI: 10.1016/0016-6480(92)90028-i] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
The present work was carried out to study the in vitro effects of mammalian gonadotropin-releasing hormone (mGnRH) on Rana esculenta and Triturus carnifex testis production of prostaglandin F2 alpha (PGF2 alpha) and sex steroid hormones during the prereproduction, reproduction, and postreproduction periods. In R. esculenta, testicular PGF2 alpha release was lower during postreproduction, and mGnRH increased PGF2 alpha in prereproduction and reproduction. Androgens were higher during prereproduction, and mGnRH induced an androgens increase in prereproduction and reproduction. In T. carnifex testicular PGF2 alpha release was lower during reproduction, and mGnRH increased PGF2 alpha in prereproduction and reproduction. Androgens were higher in reproduction and lower in postreproduction, and mGnRH induced an androgens increase in reproduction. Estradiol-17 beta release was higher in postreproduction, and mGnRH induced an estradiol decrease in reproduction and an increase in postreproduction. These results seem to indicate the involvement of PGF2 alpha in the testicular reproductive activity, and a similar mGnRH mechanism of action, both in R. esculenta and in T. carnifex. In addition, taken together with previous studies, they seem to suggest that the relationship found between mGnRH and PGF2 alpha or sex steroids could be widespread in amphibians.
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Affiliation(s)
- A Gobbetti
- Department of Molecular, Cellular, Animal Biology, University of Camerino, Italy
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Anderson L, Hoyland J, Mason WT, Eidne KA. Characterization of the gonadotrophin-releasing hormone calcium response in single alpha T3-1 pituitary gonadotroph cells. Mol Cell Endocrinol 1992; 86:167-75. [PMID: 1511786 DOI: 10.1016/0303-7207(92)90141-r] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Intracellular calcium ([Ca2+]i) was measured in single immortalized gonadotroph alpha T3-1 cells using dual wavelength fluorescence microscopy combined with dynamic video imaging. Gonadotrophin-releasing hormone (GnRH, 10(-8) M) produced a biphasic rise in [Ca2+]i which could be abolished by a GnRH antagonist. The initial calcium transient was complete within seconds while the smaller secondary plateau phase lasted several minutes. The calcium spike was reduced by nifedipine (10(-6) M), a calcium channel blocker, and thapsigargin (10(-6) M) which inhibits inositol 1,4,5-trisphosphate (IP3) mediated release of [Ca2+]i but abolished by the intracellular calcium antagonist TMB-8 (10(-6) M). The secondary phase was reduced following pretreatment with either nifedipine or the protein kinase C (PKC) antagonist, H-7 (10(-6) M). The PKC agonist PMA (phorbol 12-myristate 13-acetate, 10(-6) M) produced a small rise in basal [Ca2+]i and abolished the GnRH calcium response. The initial calcium response to GnRH therefore involves both an IP3-mediated rise in cytosolic calcium due to the release from intracellular stores and an influx of extracellular calcium through second messenger-operated calcium channels. In contrast the secondary calcium response mainly involves the influx of extracellular calcium through PKC-activated calcium channels.
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Affiliation(s)
- L Anderson
- MRC Reproductive Biology Unit, Centre for Reproductive Biology, Edinburgh, UK
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Zerani M, Gobbetti A. In vivo and in vitro studies on the effects of mGnRH on oestradiol-17 beta inter-renal production in the female frog, Rana esculenta, during the post-reproductive period. ACTA PHYSIOLOGICA SCANDINAVICA 1992; 145:377-84. [PMID: 1529724 DOI: 10.1111/j.1748-1716.1992.tb09378.x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Plasma oestradiol-17 beta was measured by RIA, in female, Rana esculenta, submitted to hypophysectomy, gonadectomy, or both, and treated with mammalian gonadotropin-releasing hormone (mGnRH), homologous pituitary homogenate, or both, during the post-reproductive period. In addition, the oestradiol-17 beta release was measured in in vitro incubations of ovaries or interrenals treated with mGnRH, pituitary, or both, during the same period. In vivo and in vitro mGnRH and/or pituitary directly stimulated the production of oestradiol-17 beta by the interrenal, but not by ovary, although the stimulatory effects of the pituitary are minor and delayed with respect to those of mGnRH. These results seem to indicate that mGnRH and pituitary, with probably different mechanisms, stimulate the interrenal to produce high levels of oestradiol which is involved in the post-reproductive refractoriness.
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Affiliation(s)
- M Zerani
- Department of Molecular, Cellular and Animal Biology, University of Camerino, Italy
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35
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Conn PM, Hawes BE, Janovick JA. Selection of models for the study of GnRH stimulated gonadotropin release prejudices the assignment of roles for mediators and modulators of hormone action. Mol Cell Endocrinol 1992; 84:C33-7. [PMID: 1316852 DOI: 10.1016/0303-7207(92)90025-2] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Affiliation(s)
- P M Conn
- Department of Pharmacology, University of Iowa College of Medicine, Iowa City 52242-1109
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36
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Netiv E, Liscovitch M, Naor Z. Delayed activation of phospholipase D by gonadotropin-releasing hormone in a clonal pituitary gonadotrope cell line (alpha T3-1). FEBS Lett 1991; 295:107-9. [PMID: 1765140 DOI: 10.1016/0014-5793(91)81396-p] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Stimulation of cultured pituitary cells from a gonadotrope lineage (alpha T3-1) by the gonadotropin-releasing hormone agonist analog [D-Trp6]GnRH (GnRH-A) resulted in a manifold increase in accumulation of phosphatidylethanol, a specific product of phospholipase D phosphatidyl transferase activity when ethanol is the phosphatidyl group acceptor. Levels of the natural lipid product of phospholipase D, phosphatidic acid, were increased 2-3-fold. Activation of phospholipase D by GnRH-A was dose- and time-dependent and was blocked by a GnRH receptor antagonist [D-pClPhe2,D-Trp3.6]GnRH. GnRH-A stimulated phospholipase D activity after a lag of 1-2 min. We conclude that in alpha T3-1 gonadotropes GnRH receptor occupancy results in delayed activation of phospholipase D which could participate in late phases of gonadotrope regulation by the neurohormone.
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Affiliation(s)
- E Netiv
- Department of Biochemistry, George S. Wise Faculty of Life Science, Tel Aviv University, Ramat Aviv, Israel
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37
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Leigh AJ, Wilson CA, Edger MJ, Tipping KE, Patel M, Chapman AJ, Whitehead SA. Stimulation of luteinizing hormone-Beta messenger ribonucleic Acid and post-translational modification of luteinizing hormone isoforms by second messengers mediating the action of gonadotrophin-releasing hormone. J Neuroendocrinol 1991; 3:605-11. [PMID: 19215530 DOI: 10.1111/j.1365-2826.1991.tb00325.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Abstract Several second messenger systems have been implicated in mediating the action of gonadotrophin-releasing hormone on the pituitary gonadotrophs and numerous studies have shown that activation of these systems induces luteinizing hormone (LH) secretion. However, it is not known how gonadotrophin-releasing hormone or the second messenger systems induce de novo LH biosynthesis and post-translational modification of the hormone. In these experiments hemipituitary glands have been perifused with drugs which activate second messengers or stimulate protein kinase C directly. The LH secretory responses have been correlated with measurements of common a and LHbeta mRNA and the molecular species of LH which were present in the pituitary perifusate after exposure to the drugs. Gonadotrophin-releasing hormone (50 ng/ml, 42 nM), with and without the presence of extracellular Ca(2+), the Ca(2+) ionophore, A23187 (10 muM), and phorbol 12-myristate (1 muM) all stimulated an increase in LHbeta mRNA compared with controls and the appearance of a different isoform of LH to that found stored in and released from the unstimulated pituitary gland. Phospholipase C was without effect on LHbeta mRNA levels and showed minimal efficacy in inducing the appearance of the different LH isoform.
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Affiliation(s)
- A J Leigh
- Departments of Obstetrics and Gynaecology St George's Hospital Medical School, Cranmer Terrace, London SW17 0RE, UK
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Rawlings S, Berry D, Leong D. Evidence for localized calcium mobilization and influx in single rat gonadotropes. J Biol Chem 1991. [DOI: 10.1016/s0021-9258(18)54632-9] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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39
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Gobbetti A, Zerani M, Mosconi G, Botte V. Effects of mammalian gonadotropin-releasing hormone on plasma level of prostaglandin F2 alpha in the water frog, Rana esculenta. Gen Comp Endocrinol 1991; 84:9-15. [PMID: 1778413 DOI: 10.1016/0016-6480(91)90059-f] [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: 12/28/2022]
Abstract
The present investigation was performed to evaluate the effects of mammalian gonadotropin-releasing hormone (mGnRH) on prostaglandin F2 alpha (PGF2 alpha) plasma level in adult male and female water frog, Rana esculenta, during three different periods of the reproductive cycle: recovery period (October), breeding period (May), and postreproductive period (June). Intact, hypophysectomized (HYP), gonadectomized (GON), and hypophysectomized-and-gonadectomized (HYP/GON) animals were injected with 0.6 micrograms of mGnRH and sacrificed 1 hr and 5 hr after peptide administration. Some of each of the groups were sacrificed without having received mGnRH. PGF2 alpha plasma levels were assessed by radioimmunoassay. Hypophysectomy induced a significant increase of PGF2 alpha levels in October and June males. mGnRH induced a significant increase of PGF2 alpha plasma levels only in HYP and HYP/GON frogs. The tissue target of this GnRH action is, at present, unknown, although interrenals could be putative responsive tissues. At present, it is also difficult to assign any physiological role to observed phenomena unless to suppose that the pituitary inhibition is not constant throughout the year. It cannot be excluded that the prostaglandin induction depends on a local paracrine action of GnRH, which could be performed outside any pituitary control.
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Affiliation(s)
- A Gobbetti
- Department of Cellular Biology, University of Camerino, Italy
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40
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Affiliation(s)
- Z Naor
- Department of Biochemistry, George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv, Israel
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41
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Leong DA. A model for intracellular calcium signaling and the coordinate regulation of hormone biosynthesis, receptors and secretion. Cell Calcium 1991; 12:255-68. [PMID: 1647877 DOI: 10.1016/0143-4160(91)90025-a] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
A two-state model for the stimulus-induced nongraded response of a single cell is formulated. Individual metestrus gonadotropes stimulated with LHRH operate as a simple switch: either on or off. At a given concentration of stimulus some gonadotropes switch on, while others do not switch on, secretion. The probability of a gonadotrope being in the secretory state is enhanced with each increment of LHRH concentration. Individual gonadotropes in a secretory state are envisioned to decrease their number of LHRH receptors and to switch off LH biosynthesis. On the other hand, individual gonadotropes that are not in a secretory state are thought to increase their number of LHRH receptors and to switch on LH biosynthesis. The group of individuals in the population that have thresholds falling in the range of a given stimulus initiate secretion. And, the group of individuals in the population that have thresholds that fall above the range of a given stimulus do not initiate secretion. More remarkable is evidence that the cells that are protected from hormone secretion nevertheless respond with a set of intracellular signals and this provides a new perspective of how they switch on hormone biosynthesis and up-regulate the LHRH receptors. These changes are envisioned to reduce the threshold of an individual cell and accordingly to enhance the probability that the cell responds in the secretory state with the next stimulus. This scheme would appear to lead to automatic cycles of secretion and biosynthesis since an individual cell can occupy only one of two states at any time and occupancy of either state promotes change to the other. This may provide a solution to the problem of how an endocrine gland might reconcile differences in the time-course of hormone secretion which occurs rapidly and hormone biosynthesis that requires a longer period of time. Parenthetically, the model may also be adapted to the case where the vast majority of individuals in the population are generally subthreshold in relation to the physiological stimulus: such an adaption leads to interesting ways of viewing the mammalian reproductive cycle and the regulation of the preovulatory LH surge. A two-state model of the internal Ca2+ store is outlined here to stimulate thought on how the intracellular signals of each binary state may switch a variety of cellular responses either on or off. The model provides a new perspective on the coordinate regulation of hormone biosynthesis, receptors, and secretion that may be useful in the final reconciliation of population studies with insights about individual cells.
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Affiliation(s)
- D A Leong
- Department of Medicine, University of Virginia, Charlottesville
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42
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Naor Z. Cyclic GMP stimulates inositol phosphate production in cultured pituitary cells: possible implication to signal transduction. Biochem Biophys Res Commun 1990; 167:982-92. [PMID: 2157436 DOI: 10.1016/0006-291x(90)90620-3] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Addition of the stable and permeable analog 8-bromo cyclic GMP (8-BR-cGMP) to myo-[2-3H]inositol prelabeled cultured rat pituitary cells results in enhanced formation of [3H]-myo-inositol monophosphate (IP1). The stimulatory effect of the cyclic nucleotide analog is additive to the effect of Li+, which accumulates IP1 via inhibition of inositol 1-monophosphatase, and also to the effect of gonadotropin releasing hormone (GnRH) which stimulates the formation of IP1, as well as that of inositol 1,4-bisphosphate (IP2) and inositol 1,4,5-trisphosphate (IP3) via enhanced hydrolysis of polyphosphoinositides. Many Ca2(+)-mobilizing hormones acting via phosphoinosite turnover also stimulate cGMP formation. The cyclic nucleotide might then serve as a modulator by further hydrolysis of phosphoinositides needed for protein kinase C activation.
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Affiliation(s)
- Z Naor
- Department of Biochemistry, George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv, Israel
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43
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Dan-Cohen H, Naor Z. Mechanism of action of gonadotropin releasing hormone upon gonadotropin secretion: involvement of protein kinase C as revealed by staurosporine inhibition and enzyme depletion. Mol Cell Endocrinol 1990; 69:135-44. [PMID: 2109710 DOI: 10.1016/0303-7207(90)90007-u] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
The role of protein kinase C (PKC) in the mechanism of action of gonadotropin-releasing hormone (GnRH) upon gonadotropin secretion is controversial and therefore was investigated in primary cultures of rat anterior pituitary cells. A relatively selective PKC inhibitor, staurosporine, inhibited both GnRH- and 12-O-tetradecanoylphorbol 13-acetate (TPA)-induced luteinizing hormone (LH) release with half-maximal inhibition (IC50) of about 80 nM. Inhibition of GnRH action was not complete suggesting also a PKC-insensitive component in GnRH-induced gonadotropin release. Staurosporine had no effect on basal LH release, or on cellular LH content, neither did the drug interfere with the binding of [125I]iodo-[D-Ser(t-Bu)6]des-Gly10-GnRH N-ethylamide to its receptor in pituitary cells. When cultured pituitary cells were incubated with TPA (1 microM) for 24-48 h no measurable cellular PKC activity could be detected. The decrease in total PKC activity was accompanied by an increase in Ca2+, phosphatidylserine (PS), diacylglycerol (DG)-insensitive activity suggesting the release of a portion of the catalytic domain of PKC (M-kinase) by the phorbol ester treatment. TPA-induced LH release was nearly abolished in PKC-depleted cells and the response to GnRH was markedly reduced (40%). The stimulatory effect of the Ca2+ ionophore, ionomycin, was not impaired in PKC-depleted cells. Impaired responses to GnRH in PKC-depleted cells were only noticed at a later phase (2-4 h) of the exocytotic response of the neurohormone. The data strongly suggest a role for PKC during the second phase of GnRH-induced gonadotropin secretion.
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Affiliation(s)
- H Dan-Cohen
- Department of Biochemistry, George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv, Israel
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44
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Chang JP, Freedman GL, de Leeuw R. Use of a pituitary cell dispersion method and primary culture system for the studies of gonadotropin-releasing hormone action in the goldfish, Carassius auratus. II. Extracellular calcium dependence and dopaminergic inhibition of gonadotropin responses. Gen Comp Endocrinol 1990; 77:274-82. [PMID: 2106469 DOI: 10.1016/0016-6480(90)90311-9] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Primary static cultures of dispersed goldfish pituitary cells obtained by controlled trypsinization released gonadotropin (GTH) in response to 2-hr stimulations of 0.1 nM to 1 microM [Trp7,Leu8]-gonadotropin-releasing hormone (sGnRH), [D-Arg6,Pro9-N-ethylamide]-sGnRH (sGnRHa), and [His5,Trp7,Tyr8]-GnRH (cGnRH-II) in a dose-dependent manner. Coincubation with 10 to 1000 nM of a dopamine agonist, apomorphine, dose dependently reduced the GTH response to increasing concentrations of sGnRH. Apomorphine at 1 microM completely abolished the dose-dependent GTH response to sGnRHa and cGnRH-II, but only partially inhibited the GTH-releasing action of high concentrations of sGnRH. Addition of calcium ionophores, 1 to 100 microM A23187 and 10 to 100 microM ionomycin, significantly increased GTH release. The ED50S of the GTH response to A23187 and ionomycin were 0.88 +/- 0.15 and 13.67 +/- 2.76 microM, respectively. Incubation with Ca2(+)-deficient media (media prepared without the addition of Ca2+ salts) did not significantly affect basal GTH release, but severely decreased the hormone response to increasing concentrations of sGnRH, A23187, and ionomycin. These results confirm the direct inhibitory dopaminergic influence on GTH release in goldfish and further suggest that extracellular Ca2+ plays a role in mediating GnRH action on gonadotropes in fish.
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Affiliation(s)
- J P Chang
- Department of Zoology, University of Alberta, Edmonton, Canada
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45
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Protein Kinase C-mediated Gonadotropin-releasing Hormone Receptor Sequestration Is Associated with Uncoupling of Phosphoinositide Hydrolysis. J Biol Chem 1989. [DOI: 10.1016/s0021-9258(18)81837-3] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
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46
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Offermanns S, Schultz G, Rosenthal W. Secretion-stimulating and secretion-inhibiting hormones stimulate high-affinity pertussis-toxin-sensitive GTPases in membranes of a pituitary cell line. EUROPEAN JOURNAL OF BIOCHEMISTRY 1989; 180:283-7. [PMID: 2564342 DOI: 10.1111/j.1432-1033.1989.tb14645.x] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Different peptide hormones influence hormone secretion in pituitary cells by diverse second messenger systems. Recent data indicate that luteinizing-hormone-releasing hormone (LHRH) stimulates and somatostatin inhibits voltage-dependent Ca2+ channels of GH3 cells via pertussis-toxin-sensitive mechanisms [Rosenthal et al. (1988) EMBO J. 7, 1627-1633]. In other pituitary cell lines, somatostatin has been shown to cause a pertussis-toxin-sensitive decrease in adenylate cyclase activity, and LHRH and thyrotropin-releasing hormone (TRH) stimulate phosphoinositol lipid hydrolysis in a pertussis-toxin-independent manner. Whether stimulation of Ca2+ influx by TRH is affected by pertussis toxin is not known. In order to elucidate which of the hormone receptors interact with pertussis-toxin-sensitive and -insensitive G-proteins, we measured the effects of LHRH, somatostatin and TRH on high-affinity GTPases in membranes of GH3 cells. In control membranes, both LHRH and TRH stimulated the high-affinity GTPase by 20%, somatostatin by 25%. Maximal hormone effects were observed at a concentration of about 1 microM. Pretreatment of cells with pertussis toxin abolished pertussis-toxin-catalyzed [32P]ADP-ribosylation of 39-40-kDa proteins in subsequently prepared membranes and reduced basal GTPase activity. The toxin also reduced by more than half the increases in GTPase activity induced by LHRH and TRH; stimulation of GTPase by somatostatin was completely suppressed. Stimulation of adenylate cyclase by vasoactive intestinal peptide (VIP) was not impaired by pretreatment of cells with pertussis toxin. Somatostatin but not LHRH and TRH decreased forskolin-stimulated adenylate cyclase activity. The results suggest that the activated receptors for LHRH and TRH act via pertussis-toxin-sensitive and -insensitive G-proteins, whereas effects of somatostatin are exclusively mediated by pertussis-toxin-sensitive G-proteins.
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Affiliation(s)
- S Offermanns
- Institut für Pharmakologie, Freie Universität Berlin
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47
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Limor R, Schvartz I, Hazum E, Ayalon D, Naor Z. Effect of guanine nucleotides on phospholipase C activity in permeabilized pituitary cells: possible involvement of an inhibitory GTP-binding protein. Biochem Biophys Res Commun 1989; 159:209-15. [PMID: 2493787 DOI: 10.1016/0006-291x(89)92424-8] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Cultured pituitary cells prelabeled with myo-[2-3H] inositol were permeabilized by ATP4-, exposed to guanine nucleotides and resealed by Mg2+. Addition of guanosine 5'-0-(3-thio triphosphate) (GTP gamma S) to permeabilized cells, or gonadotropin releasing hormone (GnRH) to resealed cells, resulted in enhanced phospholipase C activity as determined by [3H] inositol phosphate (Ins-P) production. The effect was not additive, but the combined effect was partially inhibited by guanosine 5'-0-(2-thiodiphosphate) (GDP beta S) or by neomycin. Surprisingly, addition of GDP beta S (100-600 microM) on its own resulted in a dose-related increase in [3H]Ins-P accumulation. Several nucleoside triphosphates stimulated phospholipase C activity in permeabilized pituitary cells with the following order: UTP greater than GTP gamma S greater than ATP greater than CTP. The stimulatory effect of UTP, ATP and CTP, but not GTP gamma S or GDP beta S, could also be demonstrated in normal pituitary cells suggesting a receptor-activated mechanism. GTP and GTP gamma S decreased the affinity of GnRH binding to pituitary membranes and stimulated LH secretion in permeabilized cells. These results suggest the existence of at least two G-proteins (stimulatory and inhibitory) which are involved in phospholipase C activation and GnRH action in pituitary cells.
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Affiliation(s)
- R Limor
- Department of Biochemistry, George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv, Israel
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48
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Chang JP, Morgan RO, Catt KJ. Dependence of secretory responses to gonadotropin-releasing hormone on diacylglycerol metabolism. Studies with a diacylglycerol lipase inhibitor, RHC 80267. J Biol Chem 1988. [DOI: 10.1016/s0021-9258(18)37329-0] [Citation(s) in RCA: 30] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
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49
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Stojilković SS, Chang JP, Izumi S, Tasaka K, Catt KJ. Mechanisms of secretory responses to gonadotropin-releasing hormone and phorbol esters in cultured pituitary cells. Participation of protein kinase C and extracellular calcium mobilization. J Biol Chem 1988. [DOI: 10.1016/s0021-9258(19)77835-1] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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50
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Abstract
The production of inositol phosphates in response to carbachol was studied in rat anterior pituitary tissue prelabelled with [3H]inositol. Carbachol (10 microM) stimulated inositol mono-, bis- and trisphosphate production (IP1, IP2 and IP3) by 360 +/- 49, 338 +/- 49 and 503 +/- 49 (mean +/- SEM, P less than 0.001) percent respectively during a 30 min incubation. Mean basal production was 5.4 +/- 0.3, 4.1 +/- 0.5 and 0.9 +/- 0.3 expressed as a percent of total [3H]inositol lipid for IP, IP2 and IP3 respectively. Stimulated inositol phosphate production was dose dependent and detectable after 5 min. Atropine prevented this stimulation indicating mediation via muscarinic receptors. Removal of extracellular Ca2+ reduced both basal and stimulated total inositol phosphate production by 60% and 56% respectively but did not impair carbachol-induced phosphoinositide hydrolysis per se. Pretreatment of pituitary tissue with either somatostatin (5 micrograms/ml) or pertussis toxin (1 microgram/ml) had no effect on either basal or stimulated inositol phosphate production. These results demonstrate a cholinergic stimulation of phosphatidylinositol bisphosphate (PIP2) hydrolysis in the anterior pituitary which may be important in the action of cholinergic agonists on pituitary hormone secretion.
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Affiliation(s)
- M P Schrey
- Department of Chemical Pathology, St Mary's Hospital Medical School, University of London, U.K
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