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Evans ET, Horst B, Arend RC, Mythreye K. Evolving roles of activins and inhibins in ovarian cancer pathophysiology. Am J Physiol Cell Physiol 2023; 324:C428-C437. [PMID: 36622068 PMCID: PMC9902228 DOI: 10.1152/ajpcell.00178.2022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2022] [Revised: 12/14/2022] [Accepted: 12/15/2022] [Indexed: 01/10/2023]
Abstract
Activins and inhibins are unique members of the transforming growth factor-β (TGFβ) family of growth factors, with the ability to exert autocrine, endocrine, and paracrine effects in a wide range of complex physiologic and pathologic processes. Although first isolated within the pituitary, emerging evidence suggests broader influence beyond reproductive development and function. Known roles of activin and inhibin in angiogenesis and immunity along with correlations between gene expression and cancer prognosis suggest potential roles in tumorigenesis. Here, we present a review of the current understanding of the biological role of activins and inhibins as it relates to ovarian cancers, summarizing the underlying signaling mechanisms and physiologic influence, followed by detailing their roles in cancer progression, diagnosis, and treatment.
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Affiliation(s)
- Elizabeth T Evans
- Department of Gynecologic Oncology, Heersink School of Medicine, University of Alabama School of Medicine, Birmingham, Alabama
| | - Ben Horst
- Department of Pathology, Heersink School of Medicine, University of Alabama at Birmingham, Birmingham, Alabama
| | - Rebecca C Arend
- Department of Gynecologic Oncology, Heersink School of Medicine, University of Alabama School of Medicine, Birmingham, Alabama
| | - Karthikeyan Mythreye
- Department of Pathology, Heersink School of Medicine, University of Alabama at Birmingham, Birmingham, Alabama
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Bauman WA, La Fountaine MF, Cirnigliaro CM, Kirshblum SC, Spungen AM. Testicular responses to hCG stimulation at varying doses in men with spinal cord injury. Spinal Cord 2017; 55:659-663. [PMID: 28220820 PMCID: PMC5501758 DOI: 10.1038/sc.2017.8] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2016] [Revised: 01/03/2017] [Accepted: 01/06/2017] [Indexed: 11/08/2022]
Abstract
STUDY DESIGN Prospective. OBJECTIVES To test whether provocative stimulation of the testes identifies men with chronic spinal cord injury (SCI), a population in which serum testosterone concentrations are often depressed, possibly due to gonadal dysfunction. To accomplish this objective, conventional and lower than the conventional doses of human chorionic gonadotropin (hCG) were administered. METHODS Thirty men with chronic SCI (duration of injury >1 year; 18 and 65 years old; 16 eugonadal (>12.1 nmol l-1) and 14 hypogonadal (⩽12.1 nmol l-1)) or able-bodied (AB) men (11 eugonadal and 27 hypogonadal) were recruited for the study. Stimulation tests were performed to quantify testicular responses to the intramuscular administration of hCG at three dose concentrations (ithat is, 400, 2000 and 4000 IU). The hCG was administered on two consecutive days, and blood was collected for serum testosterone in the early morning prior to each of the two injections; subjects returned on day 3 for a final blood sample collection. RESULTS The average gonadal response in the SCI and AB groups to each dose of hCG was not significantly different in the hypogonadal or eugonadal subjects, with the mean serum testosterone concentrations in all groups demonstrating an adequate response. CONCLUSIONS This work confirmed the absence of primary testicular dysfunction without additional benefit demonstrated of provocative stimulation of the testes with lower than conventional doses of hCG. Our findings support prior work that suggested a secondary testicular dysfunction that occurs in a majority of those with SCI and depressed serum testosterone concentrations.
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Affiliation(s)
- William A. Bauman
- Department of Veterans Affairs Rehabilitation Research & Development Service National Center for the Medical Consequences of Spinal Cord Injury, James J. Peters Veterans Affairs Medical Center, Bronx, NY, USA
- Department of Medicine, Icahn School of Medicine at Mount Sinai, New York, NY, USA
- Department of Rehabilitation Medicine, Icahn School of Medicine at Mount Sinai, New York, NY, USA
| | - Michael F. La Fountaine
- Department of Veterans Affairs Rehabilitation Research & Development Service National Center for the Medical Consequences of Spinal Cord Injury, James J. Peters Veterans Affairs Medical Center, Bronx, NY, USA
- Department of Medicine, Icahn School of Medicine at Mount Sinai, New York, NY, USA
- School of Health and Medical Sciences, Seton Hall University, South Orange, NJ
| | - Christopher M. Cirnigliaro
- Department of Veterans Affairs Rehabilitation Research & Development Service National Center for the Medical Consequences of Spinal Cord Injury, James J. Peters Veterans Affairs Medical Center, Bronx, NY, USA
| | - Steven C. Kirshblum
- Kessler Institute for Rehabilitation, West Orange, NJ
- Department of Physical Medicine and Rehabilitation, Rutgers New Jersey Medical School, Newark, NJ, USA
| | - Ann M. Spungen
- Department of Veterans Affairs Rehabilitation Research & Development Service National Center for the Medical Consequences of Spinal Cord Injury, James J. Peters Veterans Affairs Medical Center, Bronx, NY, USA
- Department of Medicine, Icahn School of Medicine at Mount Sinai, New York, NY, USA
- Department of Rehabilitation Medicine, Icahn School of Medicine at Mount Sinai, New York, NY, USA
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Janjic MM, Stojilkovic SS, Bjelobaba I. Intrinsic and Regulated Gonadotropin-Releasing Hormone Receptor Gene Transcription in Mammalian Pituitary Gonadotrophs. Front Endocrinol (Lausanne) 2017; 8:221. [PMID: 28928715 PMCID: PMC5591338 DOI: 10.3389/fendo.2017.00221] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/19/2017] [Accepted: 08/16/2017] [Indexed: 12/14/2022] Open
Abstract
The hypothalamic decapeptide gonadotropin-releasing hormone (GnRH), acting via its receptors (GnRHRs) expressed in pituitary gonadotrophs, represents a critical molecule in control of reproductive functions in all vertebrate species. GnRH-activated receptors regulate synthesis of gonadotropins in a frequency-dependent manner. The number of GnRHRs on the plasma membrane determines the responsiveness of gonadotrophs to GnRH and varies in relation to age, sex, and physiological status. This is achieved by a complex control that operates at transcriptional, translational, and posttranslational levels. This review aims to overview the mechanisms of GnRHR gene (Gnrhr) transcription in mammalian gonadotrophs. In general, Gnrhr exhibits basal and regulated transcription activities. Basal Gnrhr transcription appears to be an intrinsic property of native and immortalized gonadotrophs that secures the presence of a sufficient number GnRHRs to preserve their functionality independently of the status of regulated transcription. On the other hand, regulated transcription modulates GnRHR expression during development, reproductive cycle, and aging. GnRH is crucial for regulated Gnrhr transcription in native gonadotrophs but is ineffective in immortalized gonadotrophs. In rat and mouse, both basal and GnRH-induced Gnrhr transcription rely primarily on the protein kinase C signaling pathway, with subsequent activation of mitogen-activated protein kinases. Continuous GnRH application, after a transient stimulation, shuts off regulated but not basal transcription, suggesting that different branches of this signaling pathway control transcription. Pituitary adenylate cyclase-activating polypeptide, but not activins, contributes to the regulated transcription utilizing the protein kinase A signaling pathway, whereas a mechanisms by which steroid hormones modulate Gnrhr transcription has not been well characterized.
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Affiliation(s)
- Marija M. Janjic
- Department of Neurobiology, Institute for Biological Research “Sinisa Stankovic”, University of Belgrade, Belgrade, Serbia
| | - Stanko S. Stojilkovic
- Section on Cellular Signaling, Eunice Kennedy Shiver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, United States
| | - Ivana Bjelobaba
- Department of Neurobiology, Institute for Biological Research “Sinisa Stankovic”, University of Belgrade, Belgrade, Serbia
- *Correspondence: Ivana Bjelobaba,
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Namwanje M, Brown CW. Activins and Inhibins: Roles in Development, Physiology, and Disease. Cold Spring Harb Perspect Biol 2016; 8:cshperspect.a021881. [PMID: 27328872 DOI: 10.1101/cshperspect.a021881] [Citation(s) in RCA: 148] [Impact Index Per Article: 18.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Since their original discovery as regulators of follicle-stimulating hormone (FSH) secretion and erythropoiesis, the TGF-β family members activin and inhibin have been shown to participate in a variety of biological processes, from the earliest stages of embryonic development to highly specialized functions in terminally differentiated cells and tissues. Herein, we present the history, structures, signaling mechanisms, regulation, and biological processes in which activins and inhibins participate, including several recently discovered biological activities and functional antagonists. The potential therapeutic relevance of these advances is also discussed.
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Affiliation(s)
- Maria Namwanje
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas 77030
| | - Chester W Brown
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas 77030 Department of Pediatrics, Baylor College of Medicine, Houston, Texas 77030 Texas Children's Hospital, Houston, Texas 77030
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Makanji Y, Zhu J, Mishra R, Holmquist C, Wong WPS, Schwartz NB, Mayo KE, Woodruff TK. Inhibin at 90: from discovery to clinical application, a historical review. Endocr Rev 2014; 35:747-94. [PMID: 25051334 PMCID: PMC4167436 DOI: 10.1210/er.2014-1003] [Citation(s) in RCA: 103] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
When it was initially discovered in 1923, inhibin was characterized as a hypophysiotropic hormone that acts on pituitary cells to regulate pituitary hormone secretion. Ninety years later, what we know about inhibin stretches far beyond its well-established capacity to inhibit activin signaling and suppress pituitary FSH production. Inhibin is one of the major reproductive hormones involved in the regulation of folliculogenesis and steroidogenesis. Although the physiological role of inhibin as an activin antagonist in other organ systems is not as well defined as it is in the pituitary-gonadal axis, inhibin also modulates biological processes in other organs through paracrine, autocrine, and/or endocrine mechanisms. Inhibin and components of its signaling pathway are expressed in many organs. Diagnostically, inhibin is used for prenatal screening of Down syndrome as part of the quadruple test and as a biochemical marker in the assessment of ovarian reserve. In this review, we provide a comprehensive summary of our current understanding of the biological role of inhibin, its relationship with activin, its signaling mechanisms, and its potential value as a diagnostic marker for reproductive function and pregnancy-associated conditions.
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Affiliation(s)
- Yogeshwar Makanji
- Department of Obstetrics and Gynecology (Y.M., J.Z., C.H., W.P.S.W., T.K.W.), Feinberg School of Medicine, Northwestern University, Chicago, Illinois 60610; Center for Molecular Innovation and Drug Discovery (R.M., C.H.), Chemistry of Life Processes Institute, Northwestern University, Evanston, Illinois 60208; and Department of Molecular Biosciences (N.B.S., K.E.M., T.K.W.), Center for Reproductive Science, Northwestern University, Evanston, Illinois 60208
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del Valle L, Bustos-Obregón E, Gonzales GF. Serum reproductive hormone levels and sperm production in male adult rats after treatment witharresting, a fraction obtained from seminiferous tubules conditioned medium. Andrologia 2009. [DOI: 10.1111/j.1439-0272.2003.tb00872.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
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Robertson DM, Hale GE, Jolley D, Fraser IS, Hughes CL, Burger HG. Interrelationships between ovarian and pituitary hormones in ovulatory menstrual cycles across reproductive age. J Clin Endocrinol Metab 2009; 94:138-44. [PMID: 18854393 DOI: 10.1210/jc.2008-1684] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/11/2023]
Abstract
CONTEXT Ovarian hormones regulate pituitary gonadotropin secretion across the menstrual cycle via negative and positive feedback mechanisms. The contribution of individual hormones is complex and is a continuing area of research. OBJECTIVE The aim of the study was to identify relationships between LH/FSH and estradiol, progesterone, inhibin A, inhibin B, and anti-Mullerian hormone (AMH) in ovulatory menstrual cycles across reproductive age. DESIGN Serum ovarian and pituitary hormones were studied in a group of young (<35 yr; n = 21) and older (>45 yr; n = 55) women. The slopes of the regression lines relating the ovarian and pituitary hormones were determined by multiple linear regression analysis and expressed with 95% confidence intervals for each ovarian hormone, with FSH and LH as independent variables. Both simultaneous and delayed (time lagged) relationships were examined. RESULTS Clear associations were evident for the lagged prediction of FSH, with significant negative associations being evident with inhibin B and AMH in the follicular phase and with estradiol, inhibin B, progesterone, and AMH in the luteal phase. For the lagged prediction of LH, significant positive and negative associations were observed with estradiol and inhibin B, respectively, in the follicular phase and a negative association with progesterone and inhibin B in the luteal phase. CONCLUSIONS It is concluded that in the follicular phase, inhibin B is a major feedback regulator of FSH and may also be a negative feedback regulator of LH. AMH may be indirectly involved in FSH regulation.
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Affiliation(s)
- David M Robertson
- Prince Henry's Institute of Medical Research, P.O. Box 5152, Clayton, Victoria 3168, Australia.
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Moore JP, Winters SJ. Weaning and the developmental changes in follicle-stimulating hormone, pituitary adenylate cyclase-activating polypeptide, and inhibin B in the male rat. Biol Reprod 2007; 78:752-60. [PMID: 18160680 DOI: 10.1095/biolreprod.107.065466] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/01/2022] Open
Abstract
Pituitary Fshb concentrations increase markedly and selectively beginning on Postnatal Day 20 in the male rat. To evaluate the factors potentially responsible for this rise in FSH, we adjusted the time of weaning, which is generally also on Day 20. Male rat pups were provided nutrients by suckling only and were weaned to laboratory chow earlier (Day 17) or later (Day 23) than normally performed in animal facilities (Day 20). Between ages 17 and 29 days, significant increases were seen in serum LH (1.4-fold) and FSH (2.4-fold) levels; pituitary expression of Lhb (5.4-fold), Fshb (21.3-fold), and inhibin beta B (Inhbb, 2.26-fold) mRNAs; and testicular expression of Inhbb (10-fold) mRNA. Concurrently, significant decreases occurred in serum inhibin B levels (1.8-fold); pituitary adenylate cyclase-activating polypeptide (Adcyap1, 4.2-fold), total follistatin (Fst, 3.5-fold), and Fst isoform 288 (5.6-fold) mRNAs; and testicular expression of inhibin beta A (8.2-fold) mRNA. Early weaning significantly increased serum FSH but not LH and increased pituitary expression of Fshb and GnRH receptor (Gnrhr) mRNAs but not Lhb. Early weaning also significantly decreased serum inhibin B but increased testicular expression of the Inhbb subunit. Early weaning also caused pituitary expression of Fst and Adcyap1 to decline earlier than in the control group. Immediately after weaning, growth accelerated substantially, and the time of weaning produced significant and differential effects on circulating leptin levels that were not related to indices of FSH production. From these observations, we propose the novel hypothesis that the increase in growth rate subsequent to weaning signals circulating inhibin B levels to fall and pituitary Adcyap1 and consequently Fst expression to decrease, and that these events together facilitate the rise in Fshb and Gnrhr expression by increasing pituitary activin signaling.
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Affiliation(s)
- Joseph P Moore
- Department of Anatomical Sciences and Neurobiology, University of Louisville School of Medicine, Louisville, Kentucky 40202, USA.
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Winters SJ, Moore JP. Intra-pituitary regulation of gonadotrophs in male rodents and primates. Reproduction 2004; 128:13-23. [PMID: 15232060 DOI: 10.1530/rep.1.00195] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Paracrine and autocrine regulation is well established in many organs including the gonads, but the notion of communication among pituitary cells is a relatively new concept. The FSH-beta and GnRH-receptor genes are up-regulated by pituitary activin and down-regulated by pituitary follistatin, and circulating inhibin disrupts this local regulation by functioning as an endogenous competitor of the activin receptor. Activin and follistatin production by folliculostellate cells may play a central role in these responses. alpha-Subunit expression is maintained at high levels in the absence of GnRH through unknown mechanisms. There is evidence that the intra-pituitary regulation of FSH-beta and GnRH-receptor gene expression may activate pubertal maturation in male rats. Finally, there are marked differences in follistatin expression and its regulation by GnRH and androgens in male primates and rats that appear to explain species differences in the differential secretion of FSH and LH, although the physiological significance of these differences is not yet known.
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Affiliation(s)
- Stephen J Winters
- Division of Endocrinology, Metabolism and Diabetes, University of Louisville, ACB-A3G11, 550 Jackson Street, Louisville, Kentucky 40202, USA.
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del Valle LJ, Bustos-Obregón E, Gonzales GF. Serum reproductive hormone levels and sperm production in male adult rats after treatment with arresting, a fraction obtained from seminiferous tubules conditioned medium. Andrologia 2004; 35:351-7. [PMID: 15018137 DOI: 10.1046/j.0303-4569.2003.00592.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
This study used seminiferous tubule (ST) segments from adult rats to condition culture medium that had been concentrated, size fractioned and administered 10-84 days to adult rats by subcutaneous or intratesticular injection and the effects on testes weight, testosterone, luteinizing hormone (LH) and FSH levels and (homogenization-resistant) epididymal sperm count were determined. The conditioned medium obtained 2 days after culture of ST was fractionated in a 30-100 kDa component. The fraction was injected subcutaneously or intratesticularly. This factor(s), named arresting, decreases sperm count in the epididymis from 13 days to 84 days of treatment without changes in serum LH or testosterone levels. The results of the present study suggest that arresting acts on spermiogenesis/spermiation and/or the entry of sperm into the epididymis from the efferent ductules.
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Affiliation(s)
- L J del Valle
- Faculty of Medicine, University of Chile, Santiago, Chile
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Burger LL, Haisenleder DJ, Aylor KW, Dalkin AC, Prendergast KA, Marshall JC. Regulation of luteinizing hormone-beta and follicle-stimulating hormone (FSH)-beta gene transcription by androgens: testosterone directly stimulates FSH-beta transcription independent from its role on follistatin gene expression. Endocrinology 2004; 145:71-8. [PMID: 14512439 DOI: 10.1210/en.2003-1047] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The gonadotropin beta-subunit mRNAs are differentially regulated by androgens. Testosterone (T) suppresses LH-beta and increases FSH-beta. We aimed to determine whether androgens regulate LH-beta and FSH-beta transcription [as measured by changes in primary transcript (PT)] and to determine whether androgens act directly on FSH-beta or via the intrapituitary activin/follistatin (FS) system. In castrate + GnRH antagonist-treated rats, T increased FSH-beta PT between 3 and 48 h. In contrast, T suppressed LH-beta PT. The increases in FSH-beta mRNA and PT were associated with reduced FS mRNA. Activin betaB mRNA was modestly suppressed. The increase in FSH-beta PT after T was androgen specific. Both T and dihydrotestosterone (DHT) increased FSH-beta PT 2-fold and decreased both FS and betaB mRNA. Estradiol suppressed FSH-beta PT 3-fold and had no effect on FS or betaB mRNAs. LH-beta PT was suppressed by DHT. To determine whether T stimulation of FSH-beta PT reflected a decrease in pituitary FS, we gave androgen in the presence of exogenous FS in vitro. T and DHT increased FSH-beta PT 2- to 3-fold. FS alone decreased FSH-beta PT 40% but did not diminish the increase FSH-beta PT in response to T. T, DHT, and FS did not affect FS mRNA, betaB mRNA, or LH-beta PT. In conclusion, androgens acting directly on the pituitary increase FSH-beta and decrease LH-beta transcription. The increase in FSH-beta PT in response to T was androgen specific and occurs in the presence of excess FS, suggesting that T stimulates FSH-beta transcription independently of modulation of FS.
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Affiliation(s)
- Laura L Burger
- Department of Internal Medicine, University of Virginia, Charlottesville, Virginia 22908, USA.
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Kakar SS, Malik MT, Winters SJ. Gonadotropin-releasing hormone receptor: cloning, expression and transcriptional regulation. PROGRESS IN BRAIN RESEARCH 2003; 141:129-47. [PMID: 12508566 DOI: 10.1016/s0079-6123(02)41089-8] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/28/2023]
Abstract
In summary, isolation of GnRH receptor cDNA, its gene, and identification of regulatory elements in the flanking region of the gene have added to our knowledge regarding the tissue-specific expression of the GnRH receptor gene, and the mechanisms that mediate and influence its transcriptional regulation. However, the interactions of the different regulatory factors (nuclear factors) and the effects of these interactions on the regulation of the GnRH receptor gene remain unclear. Due to existence of multiple promoters and transcriptional start sites in human GnRH receptor gene and the lack of a human gonadotrope cell line, the precise promoter and transcriptional start sites in human pituitary, extra-pituitary tissues and tumors have not yet been identified.
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Affiliation(s)
- Sham S Kakar
- Department of Medicine, University of Louisville, Louisville, KY 40202, USA.
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Tilbrook AJ, de Kretser DM, Clarke IJ. Influence of the degree of stimulation of the pituitary by gonadotropin-releasing hormone on the action of inhibin and testosterone to suppress the secretion of the gonadotropins in rams. Biol Reprod 2001; 64:473-81. [PMID: 11159349 DOI: 10.1095/biolreprod64.2.473] [Citation(s) in RCA: 6] [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
This experiment determined if the degree of stimulation of the pituitary gland by GnRH affects the suppressive actions of inhibin and testosterone on gonadotropin secretion in rams. Two groups (n = 5) of castrated adult rams underwent hypothalamopituitary disconnection and were given two i.v. injections of vehicle or 0.64 microg/kg of recombinant human inhibin A (rh-inhibin) 6 h apart when treated with i.m. injections of oil and testosterone propionate every 12 h for at least 7 days. Each treatment was administered when the rams were infused i.v. with 125 ng of GnRH every 4 h (i.e., slow-pulse frequency) and 125 ng of GnRH every hour (i.e., fast-pulse frequency). The FSH concentrations and LH pulse amplitude were lower and the LH concentrations higher during the fast GnRH pulse frequency. The GnRH pulse frequency did not influence the ability of rh-inhibin and testosterone to suppress FSH secretion. Testosterone did not affect LH secretion. Following rh-inhibin treatment, LH pulse amplitude decreased at the slow, but not at the fast, GnRH pulse frequency, and LH concentrations decreased at both GnRH pulse frequencies. We conclude that the degree of stimulation of the pituitary by GnRH does not influence the ability of inhibin or testosterone to suppress FSH secretion in rams. Inhibin may be capable of suppressing LH secretion under conditions of low GnRH.
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Affiliation(s)
- A J Tilbrook
- Department of Physiology, P.O. Box 13F, Monash University, Victoria, 3800, Australia.
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Ramaswamy S, Pohl CR, McNeilly AS, Winters SJ, Plant TM. The time course of follicle-stimulating hormone suppression by recombinant human inhibin A in the adult male rhesus monkey (Macaca mulatta). Endocrinology 1998; 139:3409-15. [PMID: 9681490 DOI: 10.1210/endo.139.8.6125] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
In higher primates, FSH secretion appears to be regulated by a control system consistent with that described by the classical inhibin hypothesis. The purpose of the present experiment was to examine the time course of inhibin's action to suppress FSH secretion in the intact adult male rhesus monkey. To this end, five adult males implanted with indwelling venous catheters and exhibiting typical episodic patterns of LH and testosterone (T) secretion received a 4-day i.v. infusion of recombinant human (rh) inhibin A (832 ng/h x kg) followed, after a 4-week interval, by vehicle infusion of similar duration. Changes in circulating FSH concentrations during the inhibin and vehicle infusions were determined using a sensitive homologous macaque RIA, whereas enzyme-linked immunosorbent assays were employed to track inhibin A, inhibin B, and inhibin pro-alpha-C levels during the experiment. Normal pulsatile activity in the hypothalamic-pituitary-Leydig cell axis was confirmed by monitoring changes in circulating concentrations of LH and T in 12-h windows of sequential blood collection (1200-2400 h; every 20 min) before, during, and after the rh inhibin A and vehicle infusions. Although infusion of rh inhibin A, which led to a 12 ng/ml square wave increment in circulating levels of this inhibin dimer, produced a marked decline in circulating FSH concentrations, significant suppression of the secretion of this gonadotropin was not manifest until 54 h after initiation of the infusion. Despite the marked decline in FSH secretion during the last 24 h of the 4-day infusion of recombinant hormone, circulating inhibin B and pro-alpha-C concentrations were maintained at preinfusion control levels (1 ng/ml). The finding that imposition of an exaggerated circulating inhibin signal led to suppression of FSH secretion in the male monkey only after 2 days of exposure to the hormone indicates that in this species the feedback action of testicular inhibin on FSH secretion is heavily lagged. Moreover, as the decrease in FSH did not lead to changes in native inhibin secretion, it seems reasonable to propose that the FSH-inhibin feedback loop that governs testicular function in higher primates operates with considerable hysteresis at both the pituitary and gonadal levels. The failure of dramatically elevated inhibin A levels to influence the pulsatile secretion of LH in the monkey reinforces the idea that in this species the pituitary action of testicular inhibin is specific for FSH and does not involve modulation of GnRH receptor levels.
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Affiliation(s)
- S Ramaswamy
- Department of Cell Biology and Physiology, University of Pittsburgh School of Medicine, Pennsylvania 15261, USA
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