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Monageng E, Offor U, Takalani NB, Mohlala K, Opuwari CS. A Review on the Impact of Oxidative Stress and Medicinal Plants on Leydig Cells. Antioxidants (Basel) 2023; 12:1559. [PMID: 37627554 PMCID: PMC10451682 DOI: 10.3390/antiox12081559] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2023] [Revised: 07/03/2023] [Accepted: 08/02/2023] [Indexed: 08/27/2023] Open
Abstract
Leydig cells are essential for steroidogenesis and spermatogenesis. An imbalance in the production of reactive oxygen species (ROS) and the cellular antioxidant level brings about oxidative stress. Oxidative stress (OS) results in the dysfunction of Leydig cells, thereby impairing steroidogenesis, spermatogenesis, and ultimately, male infertility. To prevent Leydig cells from oxidative insults, there needs to be a balance between the ROS production and the cellular protective capacity of antioxidants. Evidence indicates that medicinal plants could improve Leydig cell function at specific concentrations under basal or OS conditions. The increased usage of medicinal plants has been considered a possible alternative treatment for male infertility. This review aims to provide an overview of the impact of oxidative stress on Leydig cells as well as the effects of various medicinal plant extracts on TM3 Leydig cells. The medicinal plants of interest include Aspalathus linearis, Camellia sinensis, Moringa oleifera, Morinda officinale, Taraxacum officinale, Trichilia emetica, Terminalia sambesiaca, Peltophorum africanum, Ximenia caffra, Serenoa repens, Zingiber officinale, Eugenia jambolana, and a combination of dandelion and fermented rooibos (CRS-10). According to the findings obtained from studies conducted on the evaluated medicinal plants, it can, therefore, be concluded that the medicinal plants maintain the antioxidant profile of Leydig cells under basal conditions and have protective or restorative effects following exposure to oxidative stress. The available data suggest that the protective role exhibited by the evaluated plants may be attributed to their antioxidant content. Additionally, the use of the optimal dosage or concentration of the extracts in the management of oxidative stress is of the utmost importance, and the measurement of their oxidation reduction potential is recommended.
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Affiliation(s)
- Elizabeth Monageng
- Department of Medical Biosciences, Faculty of Natural Science, University of Western Cape, Cape Town 7535, South Africa
| | - Ugochukwu Offor
- School of Anatomical Sciences, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg 2193, South Africa
| | - Ndivhuho Beauty Takalani
- Department of Medical Biosciences, Faculty of Natural Science, University of Western Cape, Cape Town 7535, South Africa
| | - Kutullo Mohlala
- Department of Medical Biosciences, Faculty of Natural Science, University of Western Cape, Cape Town 7535, South Africa
| | - Chinyerum Sylvia Opuwari
- Department of Medical Biosciences, Faculty of Natural Science, University of Western Cape, Cape Town 7535, South Africa
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2
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Ajayi AF, Onaolapo MC, Omole AI, Adeyemi WJ, Oluwole DT. Mechanism associated with changes in male reproductive functions during ageing process. Exp Gerontol 2023; 179:112232. [PMID: 37315721 DOI: 10.1016/j.exger.2023.112232] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2023] [Revised: 06/07/2023] [Accepted: 06/10/2023] [Indexed: 06/16/2023]
Abstract
Ageing is a natural process with physiological changes in different body parts and has been associated with decreased reproductive capacity. Factors such as imbalance in the antioxidant defence system, vascular diseases, diabetes mellitus, accessory reproductive glands infection, obesity as well as buildup of toxic substances play a role in age-related male reproductive malfunction. Age is inversely proportional to volume of semen, sperm count, sperm progressive motility, sperm viability, normal sperm morphology. The observed negative correlation between ageing and semen indices contributes to male infertility and reproductive decline. Normal levels of ROS, plays crucial role in facilitating sperm function, such as capacitation, hyper-activation, acrosome reaction as well as sperm-oocyte fusion; however, a substantial elevation in the endogenous level of ROS, especially in reproductive tissues, usually instigates destruction of sperm cells and heightened male infertility. Contrarily, antioxidants, such as vitamins C and E, beta-carotene, and micronutrients like zinc and folate, have been found by researchers to facilitate normal semen quality and male reproductive function. Furthermore, the role of hormonal imbalance as a result of the compromised hypothalamic-pituitary-gonadal axis, Sertoli and Leydig cells disorder, and nitric oxide-medicated erectile dysfunction during ageing cannot be undermined.
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Affiliation(s)
- Ayodeji Folorunsho Ajayi
- Department of Physiology, Ladoke Akintola University of Technology, Ogbomoso, Oyo State, Nigeria; Anchor Biomed Research Institute, Ogbomoso, Oyo State, Nigeria.
| | | | - Ayomide Isaac Omole
- Department of Physiology, Ladoke Akintola University of Technology, Ogbomoso, Oyo State, Nigeria
| | | | - David Tolulope Oluwole
- Department of Physiology, Ladoke Akintola University of Technology, Ogbomoso, Oyo State, Nigeria; Department of Physiology, Crescent University, Abeokuta, Ogun-State, Nigeria
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3
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Ketchem JM, Bowman EJ, Isales CM. Male sex hormones, aging, and inflammation. Biogerontology 2023; 24:1-25. [PMID: 36596999 PMCID: PMC9810526 DOI: 10.1007/s10522-022-10002-1] [Citation(s) in RCA: 9] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2022] [Accepted: 11/15/2022] [Indexed: 01/05/2023]
Abstract
Adequate levels of androgens (eugonadism), and specifically testosterone, are vital compounds for male quality of life, longevity, and positive health outcomes. Testosterone exerts its effects by binding to the androgen receptor, which is expressed in numerous tissues throughout the body. Significant research has been conducted on the impact of this steroid hormone on skeletal, muscle and adipose tissues and on the cardiovascular, immune, and nervous systems. Testosterone levels have also been studied in relation to the impact of diseases, aging, nutrition and the environment on its circulating levels. Conversely, the impact of testosterone on health has also been evaluated with respect to its cardiac and vascular protective effects, body composition, autoimmunity and all-cause mortality. The male aging process results in decreasing testosterone levels over time. The exact mechanisms and impact of these changes in testosterone levels with age on health- and life-span are still not completely clear. Further research is needed to determine the optimal testosterone and androgen levels to protect from chronic age-related conditions such as frailty and osteoporosis.
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Affiliation(s)
- Justin M. Ketchem
- grid.410427.40000 0001 2284 9329Medical College of Georgia at Augusta University, Augusta, GA 30912 USA
| | | | - Carlos M. Isales
- grid.410427.40000 0001 2284 9329Departments of Medicine, Neuroscience and Regenerative Medicine, Augusta University, Augusta, GA 30912 USA
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Abstract
Sleep serves important biological functions, and influences health and longevity through endocrine and metabolic related systems. Sleep debt, circadian misalignment and sleep disruption from obstructive sleep apnea is widespread in modern society and accumulates with life because recovery sleep is not completely restorative. Accumulated disordered sleep throughout life impacts the ageing process and the development of age-related diseases. When epidemiological and interventional studies are considered collectively, sleep loss and lower sleep duration are associated with lower morning, afternoon and 24-h testosterone; as well as higher afternoon, but not morning or 24-h cortisol. These reciprocal changes imbalances anabolic-catabolic signaling because testosterone and cortisol are respectively the main anabolic and catabolic signals in man. Fixing testosterone-cortisol balance by means of a novel dual-hormone clamp mitigates the induction of insulin resistance by sleep restriction and provided the first proof-of-concept that the metabolic harm from sleep loss can be ameliorated by approaches that do not require sleeping more. Obstructive sleep apnea is associated with lower testosterone, even after controlling for age and obesity whereas the conclusion that continuous positive airway pressure therapy has no effect on testosterone is premature because available studies are underpowered and better-quality studies suggest otherwise. High dose testosterone therapy induces OSA, but more physiological dosing may not; and this effect may be transient or may dissipate with longer term therapy. Studies investigating the origin of the diurnal testosterone rhythm, the effect of circadian misalignment on testosterone-cortisol balance, and methods to mitigate metabolic harm, are required.
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Affiliation(s)
- Peter Y Liu
- Division of Endocrinology, Metabolism and Nutrition, Department of Medicine, Harbor UCLA Medical Center and The Lundquist Institute, 1124 W Carson St., Box 446, Torrance, CA, 90502, USA.
- David Geffen School of Medicine at UCLA, Los Angeles, CA, USA.
| | - Radha T Reddy
- Division of Endocrinology, Metabolism and Nutrition, Department of Medicine, Harbor UCLA Medical Center and The Lundquist Institute, 1124 W Carson St., Box 446, Torrance, CA, 90502, USA
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Anawalt BD, Matsumoto AM. Aging and androgens: Physiology and clinical implications. Rev Endocr Metab Disord 2022; 23:1123-1137. [PMID: 36459352 PMCID: PMC10370404 DOI: 10.1007/s11154-022-09765-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 10/12/2022] [Indexed: 12/04/2022]
Abstract
In men > ~35 years, aging is associated with perturbations in the hypothalamus-pituitary-testicular axis and declining serum testosterone concentrations. The major changes are decreased gonadotropin-releasing hormone (GnRH) outflow and decreased Leydig cell responsivity to stimulation by luteinizing hormone (LH). These physiologic changes increase the prevalence of biochemical secondary hypogonadism-a low serum testosterone concentration without an elevated serum LH concentration. Obesity, medications such as opioids or corticosteroids, and systemic disease further reduce GnRH and LH secretion and might result in biochemical or clinical secondary hypogonadism. Biochemical secondary hypogonadism related to aging often remits with weight reduction and avoidance or treatment of other factors that suppress GnRH and LH secretion. Starting at age ~65-70, progressive Leydig cell dysfunction increases the prevalence of biochemical primary hypogonadism-a low serum testosterone concentration with an elevated serum LH concentration. Unlike biochemical secondary hypogonadism in older men, biochemical primary hypogonadism is generally irreversible. The evaluation of low serum testosterone concentrations in older men requires a careful assessment for symptoms, signs and causes of male hypogonadism. In older men with a body mass index (BMI) ≥ 30, biochemical secondary hypogonadism and without an identifiable cause of hypothalamus or pituitary pathology, weight reduction and improvement of overall health might reverse biochemical hypogonadism. For older men with biochemical primary hypogonadism, testosterone replacement therapy might be beneficial. Because aging is associated with decreased metabolism of testosterone and increased tissue-specific androgen sensitivity, lower dosages of testosterone replacement therapy are often effective and safer in older men.
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Affiliation(s)
- Bradley D Anawalt
- Department of Medicine, University of Washington School of Medicine, Department of Medicine, 1959 NE Pacific Avenue, Box 356420, Seattle, WA, 98195, USA.
| | - Alvin M Matsumoto
- Department of Medicine, University of Washington School of Medicine, Department of Medicine, 1959 NE Pacific Avenue, Box 356420, Seattle, WA, 98195, USA
- Geriatric Research, Education and Clinical Center VA Puget Sound Health Care System, 1660 South Columbian Way (S-182-GRECC), Seattle, WA, 98118, USA
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Gibbison B, Keenan DM, Roelfsema F, Evans J, Phillips K, Rogers CA, Angelini GD, Lightman SL. Response to Letter to the Editor: "Dynamic Pituitary-Adrenal Interactions in the Critically Ill After Cardiac Surgery". J Clin Endocrinol Metab 2020; 105:5865825. [PMID: 32609339 DOI: 10.1210/clinem/dgaa422] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/15/2020] [Accepted: 06/24/2020] [Indexed: 11/19/2022]
Affiliation(s)
- Ben Gibbison
- Department of Anaesthesia, Bristol Medical School, University of Bristol, Bristol, UK
| | - Daniel M Keenan
- Dept of Statistics, University of Virginia, Charlottesville, Virginia
| | - Ferdinand Roelfsema
- Department of Internal Medicine, Section Endocrinology, University of Leiden, Leiden, The Netherlands
| | - Jon Evans
- Clinical Trials and Evaluation Unit, Bristol Trials Centre, University of Bristol, Bristol, UK
| | - Kirsty Phillips
- Dept of Pathology, University Hospitals Bristol NHS Foundation Trust, Bristol, UK
| | - Chris A Rogers
- Clinical Trials and Evaluation Unit, Bristol Trials Centre, University of Bristol, Bristol, UK
| | - Gianni D Angelini
- Dept of Cardiac Surgery, Bristol Medical School, University of Bristol, Bristol, UK
| | - Stafford L Lightman
- Henry Wellcome Laboratories for Integrative Neuroscience and Endocrinology, University of Bristol, Bristol, UK
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Roelfsema F, Liu PY, Takahashi PY, Yang RJ, Veldhuis JD. Dynamic Interactions Between LH and Testosterone in Healthy Community-Dwelling Men: Impact of Age and Body Composition. J Clin Endocrinol Metab 2020; 105:5650390. [PMID: 31790144 PMCID: PMC7025815 DOI: 10.1210/clinem/dgz246] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/09/2019] [Accepted: 11/30/2019] [Indexed: 11/19/2022]
Abstract
BACKGROUND Aging is associated with diminished testosterone (Te) secretion, which may be attributed to Leydig cell dysfunction, decreased pituitary stimulation, and altered Te feedback. OBJECTIVE To study all regulatory nodes-gonadotropin-releasing hormone (GnRH), luteinizing hormone (LH) and Leydig cell-in the same cohort of healthy men. STUDY DESIGN This was a placebo-controlled, blinded, prospectively randomized cross-over study in 40 men, age range 19 to 73 years, and body mass index (BMI) range 20 to 34.3 kg/m2. A submaximal dose of the GnRH antagonist ganirelix was used to assess outflow of GnRH, by calculating the difference between LH output during the control arm and ganirelix arm. Ketoconazole (a steroidogenic inhibitor) was used to estimate feedback, by the difference in LH output during the ketoconazole and control arm. High-dose ganirelix and repeated LH infusions were used to measure testicular responsivity. Blood sampling was performed at 10-minute intervals. RESULTS There were age-related, but not body composition-related decreases in estimated GnRH secretion, the feedback strength of Te on LH, and Leydig cell responsivity to LH, accompanied by changes in approximate entropy. Bioavailable Te levels were negatively related to both age and computed tomography (CT)-estimated abdominal visceral mass (AVF), without interaction between these variables. The LH response to a submaximal dose of GnRH was independent of age and AVF. CONCLUSION Advancing age is associated with (1) attenuated bioavailable Te secretion caused by diminished GnRH outflow and not by decreased GnRH responsivity of the gonadotrope, (2) diminished testicular responsivity to infused LH pulses, and (3) partial compensation by diminished Te feedback on central gonadotropic regulation.
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Affiliation(s)
- Ferdinand Roelfsema
- Department of Internal Medicine, Section Endocrinology and Metabolism, Leiden University Medical Center, Leiden, The Netherlands
| | - Peter Y Liu
- Department of Medicine, David Geffen School of Medicine at UCLA, Harbor-UCLA Medical Center and Los Angeles Biomedical Research Institute, Los Angeles, California
| | - Paul Y Takahashi
- Department of Primary Care Internal Medicine, Mayo Clinic, Rochester, Minnesota
| | - Rebecca J Yang
- Endocrine Research Unit, Mayo School of Graduate Medical Education, Center for Translational Science Activities, Mayo Clinic, Rochester, Minnesota
| | - Johannes D Veldhuis
- Endocrine Research Unit, Mayo School of Graduate Medical Education, Center for Translational Science Activities, Mayo Clinic, Rochester, Minnesota
- Correspondence: Johannes Veldhuis, MD, Endocrine Research Unit, Mayo Clinic, 200 First Street SW, Rochester, MN 55906, USA. Email
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8
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Swee DS, Gan EH. Late-Onset Hypogonadism as Primary Testicular Failure. Front Endocrinol (Lausanne) 2019; 10:372. [PMID: 31244778 PMCID: PMC6581721 DOI: 10.3389/fendo.2019.00372] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/08/2019] [Accepted: 05/24/2019] [Indexed: 12/21/2022] Open
Affiliation(s)
- Du Soon Swee
- Endocrine Unit, Royal Victoria Infirmary, Newcastle upon Tyne, United Kingdom
- Department of Endocrinology, Singapore General Hospital, Singapore, Singapore
| | - Earn H. Gan
- Institute of Genetic Medicine, International Centre for Life, Newcastle University, Newcastle upon Tyne, United Kingdom
- South Tyneside and Sunderland NHS Foundation Trust, Newcastle upon Tyne, United Kingdom
- *Correspondence: Earn H. Gan
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9
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Muratoğlu S, Akarca Dizakar OS, Keskin Aktan A, Ömeroğlu S, Akbulut KG. The protective role of melatonin and curcumin in the testis of young and aged rats. Andrologia 2018; 51:e13203. [PMID: 30467869 DOI: 10.1111/and.13203] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2018] [Revised: 09/28/2018] [Accepted: 10/29/2018] [Indexed: 01/06/2023] Open
Abstract
We aimed to investigate the effect of melatonin and curcumin treatment on oxidative stress, apoptosis, and histology of testicular tissue in our study. Four groups were formed using young (4 months old, n = 6) and aged (20-22 months old, n = 18) male Wistar albino rats: (a) Young control (1% ethanol:phosphate-buffered saline [PBS], subcutaneously [s.c.]); (b) Aged control (CTL; n = 6, 1% ethanol:PBS, s.c.); (c) Aged Melatonin (MLT; n = 6, 10 mg/kg, s.c.); (d) Aged Curcumin (CUR; n = 6, 30 mg/kg, i.p.). At the end of 21 days, the rats were sacrificed, and testicular tissues were removed. Malondialdehyde (MDA) in the testicular tissue was determined with thiobarbituric acid reactive substances formation, and glutathione (GSH) was determined with modified Ellman method; testosterone level was determined with chemiluminescence method and histologic changes were determined with Haematoxylin-Eosin and Johnsen's scoring; Apoptotic cell counts were made with TUNEL staining of seminiferous tubule in testis. With ageing, MDA level increased in testicular tissue, but GSH and blood testosterone levels decreased. Melatonin treatment for aged rats significantly decreased Paired total testicular/body weight ratio compared to aged control group (p < 0.05). Curcumin treatment for aged rats significantly increased GSH level compared to the aged control group (p < 0.05). Besides, melatonin and curcumin treatment significantly decreased the number of apoptotic cells and significantly increased Johnsen's score (p < 0.05).
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Affiliation(s)
- Saide Muratoğlu
- Department of Physiology, Gazi University School of Medicine, Ankara, Turkey
| | - Ozen S Akarca Dizakar
- Department of Histology and Embryology, Gazi University School of Medicine, Ankara, Turkey
| | - Arzu Keskin Aktan
- Department of Physiology, Gazi University School of Medicine, Ankara, Turkey.,Department of Physical Therapy and Rehabilitation, Health Science Faculty, Nuh Naci Yazgan University, Kayseri, Turkey
| | - Suna Ömeroğlu
- Department of Histology and Embryology, Gazi University School of Medicine, Ankara, Turkey
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Eendebak RJAH, Ahern T, Swiecicka A, Pye SR, O'Neill TW, Bartfai G, Casanueva FF, Maggi M, Forti G, Giwercman A, Han TS, Słowikowska-Hilczer J, Lean MEJ, Punab M, Pendleton N, Keevil BG, Vanderschueren D, Rutter MK, Tampubolon G, Goodacre R, Huhtaniemi IT, Wu FCW. Elevated luteinizing hormone despite normal testosterone levels in older men-natural history, risk factors and clinical features. Clin Endocrinol (Oxf) 2018; 88:479-490. [PMID: 29178359 DOI: 10.1111/cen.13524] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/16/2017] [Revised: 11/05/2017] [Accepted: 11/21/2017] [Indexed: 11/29/2022]
Abstract
OBJECTIVE Elevated luteinizing hormone (LH) with normal testosterone (T) suggests compensated dysregulation of the gonadal axis. We describe the natural history, risk factors and clinical parameters associated with the development of high LH (HLH, LH >9.4 U/L) in ageing men with normal T (T ≥ 10.5 nmol/L). DESIGN, PATIENTS AND MEASUREMENTS We conducted a 4.3-year prospective observational study of 3369 community-dwelling European men aged 40-79 years. Participants were classified as follows: incident (i) HLH (n = 101, 5.2%); persistent (p) HLH (n = 128, 6.6%); reverted (r) HLH (n = 46, 2.4%); or persistent normal LH (pNLH, n = 1667, 85.8%). Potential predictors and changes in clinical features associated with iHLH and rHLH were analysed using regression models. RESULTS Age >70 years (OR = 4.12 [2.07-8.20]), diabetes (OR = 2.86 [1.42-5.77]), chronic pain (OR = 2.53 [1.34-4.77]), predegree education (OR = 1.79 [1.01-3.20]) and low physical activity (PASE ≤ 78, OR = 2.37 [1.24-4.50]) predicted development of HLH. Younger age (40-49 years, OR = 8.14 [1.35-49.13]) and nonsmoking (OR = 5.39 [1.48-19.65]) predicted recovery from HLH. Men with iHLH developed erectile dysfunction, poor health, cardiovascular disease (CVD) and cancer more frequently than pNLH men. In pHLH men, comorbidities, including CVD, developed more frequently, and cognitive and physical function deteriorated more, than in pNLH men. Men with HLH developed primary hypogonadism more frequently (OR = 15.97 [5.85-43.60]) than NLH men. Men with rHLH experienced a small rise in BMI. CONCLUSIONS Elevation of LH with normal T is predicted by multiple factors, reverts frequently and is not associated with unequivocal evidence of androgen deficiency. High LH is a biomarker for deteriorating health in aged men who tend to develop primary hypogonadism.
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Affiliation(s)
- Robert J A H Eendebak
- Manchester Academic Health Sciences Centre, Faculty of Medical and Human Sciences, Institute of Human Development, Centre for Endocrinology and Diabetes, Andrology Research Unit, University of Manchester, Manchester, UK
| | - Tomas Ahern
- Manchester Academic Health Sciences Centre, Faculty of Medical and Human Sciences, Institute of Human Development, Centre for Endocrinology and Diabetes, Andrology Research Unit, University of Manchester, Manchester, UK
| | - Agnieszka Swiecicka
- Manchester Academic Health Sciences Centre, Faculty of Medical and Human Sciences, Institute of Human Development, Centre for Endocrinology and Diabetes, Andrology Research Unit, University of Manchester, Manchester, UK
| | - Stephen R Pye
- Arthritis Research UK Centre for Epidemiology, Division of Musculoskeletal & Dermatological Sciences, Faculty of Biology, Medicine and Health, University of Manchester and NIHR Manchester Musculoskeletal Biomedical Research Unit, Central Manchester NHS Foundation Trust, Manchester, UK
| | - Terence W O'Neill
- Arthritis Research UK Centre for Epidemiology, Division of Musculoskeletal & Dermatological Sciences, Faculty of Biology, Medicine and Health, University of Manchester and NIHR Manchester Musculoskeletal Biomedical Research Unit, Central Manchester NHS Foundation Trust, Manchester, UK
| | - Gyorgy Bartfai
- Department of Obstetrics, Gynaecology and Andrology, Albert Szent-György Medical University, Szeged, Hungary
| | - Felipe F Casanueva
- Department of Medicine, Santiago de Compostela University, Complejo Hospitalario Universitario de Santiago (CHUS), Santiago de Compostela, Spain
- Instituto Salud Carlos III, CIBER de Fisiopatología Obesidad y Nutricion(CB06/03), Santiago de Compostela, Spain
| | - Mario Maggi
- Sexual Medicine and Andrology Unit, Department of Experimental and Clinical Biomedical Sciences "Mario Serio", University of Florence, Florence, Italy
| | - Gianni Forti
- Sexual Medicine and Andrology Unit, Department of Experimental and Clinical Biomedical Sciences "Mario Serio", University of Florence, Florence, Italy
| | | | - Thang S Han
- Institute of Cardiovascular Research, Royal Holloway University of London (ICR2UL) and Ashford and St Peter's NHS Foundation Trust, Egham, Surrey, UK
| | | | - Michael E J Lean
- Department of Human Nutrition, University of Glasgow, Glasgow, UK
| | - Margus Punab
- Andrology Unit, United Laboratories of Tartu University Clinics, Tartu, Estonia
| | - Neil Pendleton
- Centre for Clinical and Cognitive Neuroscience, University of Manchester, Manchester, UK
| | - Brian G Keevil
- Department of Clinical Biochemistry, University Hospital of South Manchester, Manchester, UK
| | - Dirk Vanderschueren
- Department of Andrology and Endocrinology, Katholieke Universiteit Leuven, Leuven, Belgium
| | - Martin K Rutter
- Manchester Diabetes Centre, Central Manchester University Hospitals NHS Foundation Trust, Manchester Academic Health Science, Manchester, UK
| | - Gindo Tampubolon
- Cathie Marsh Institute for Social Research. Faculty of Humanities, University of Manchester, Manchester, UK
| | - Royston Goodacre
- School of Chemistry, Manchester Institute for Biotechnology, University of Manchester, Manchester, UK
| | - Ilpo T Huhtaniemi
- Department of Surgery and Cancer, Institute of Reproductive and Developmental Biology, Imperial College London, Hammersmith Campus, London, UK
- Department of Physiology, Institute of Biomedicine, University of Turku, Turku, Finland
| | - Frederick C W Wu
- Manchester Academic Health Sciences Centre, Faculty of Medical and Human Sciences, Institute of Human Development, Centre for Endocrinology and Diabetes, Andrology Research Unit, University of Manchester, Manchester, UK
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11
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Wang Y, Chen F, Ye L, Zirkin B, Chen H. Steroidogenesis in Leydig cells: effects of aging and environmental factors. Reproduction 2017; 154:R111-R122. [PMID: 28747539 DOI: 10.1530/rep-17-0064] [Citation(s) in RCA: 144] [Impact Index Per Article: 20.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2017] [Revised: 07/14/2017] [Accepted: 07/26/2017] [Indexed: 12/28/2022]
Abstract
Serum testosterone (TS) levels decrease with aging in both humans and rodents. Using the rat as a model system, it was found that age-related reductions in serum TS were not due to loss of Leydig cells, but rather to the reduced ability of the Leydig cells to produce TS in response to luteinizing hormone (LH). Detailed analyses of the steroidogenic pathway have suggested that two defects along the pathway, LH-stimulated cAMP production and cholesterol transport to and into the mitochondria, are of particular importance in age-related reductions in TS production. Although the mechanisms involved in these defects are far from certain, increasing oxidative stress appears to play a particularly important role. Interestingly, increased oxidative stress also appears to be involved in the suppressive effects of endocrine disruptors on Leydig cell TS production.
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Affiliation(s)
- Yiyan Wang
- The Second Affiliated Hospital and Yuying Children's Hospital of Wenzhou Medical UniversityWenzhou, Zhejiang, China.,Department of Biochemistry and Molecular BiologyJohns Hopkins Bloomberg School of Public Health, Baltimore, Maryland, USA
| | - Fenfen Chen
- The Second Affiliated Hospital and Yuying Children's Hospital of Wenzhou Medical UniversityWenzhou, Zhejiang, China
| | - Leping Ye
- The Second Affiliated Hospital and Yuying Children's Hospital of Wenzhou Medical UniversityWenzhou, Zhejiang, China
| | - Barry Zirkin
- Department of Biochemistry and Molecular BiologyJohns Hopkins Bloomberg School of Public Health, Baltimore, Maryland, USA
| | - Haolin Chen
- The Second Affiliated Hospital and Yuying Children's Hospital of Wenzhou Medical UniversityWenzhou, Zhejiang, China .,Department of Biochemistry and Molecular BiologyJohns Hopkins Bloomberg School of Public Health, Baltimore, Maryland, USA
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12
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Liu PY. Assessing new peptides that may be involved in the physiological regulation of the gonadal axis in humans: gonadotrophin inhibitory hormone. Clin Endocrinol (Oxf) 2017; 86:658-659. [PMID: 28295469 DOI: 10.1111/cen.13328] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/23/2017] [Revised: 03/03/2017] [Accepted: 03/07/2017] [Indexed: 11/28/2022]
Affiliation(s)
- Peter Y Liu
- Division of Endocrinology, Department of Medicine, Harbor-UCLA Medical Center and Los Angeles Biomedical Research Institute (LA BioMed), Torrance, CA, USA
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13
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Keenan DM, Veldhuis JD. Pulsatility of Hypothalamo-Pituitary Hormones: A Challenge in Quantification. Physiology (Bethesda) 2017; 31:34-50. [PMID: 26674550 DOI: 10.1152/physiol.00027.2015] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Neuroendocrine systems control many of the most fundamental physiological processes, e.g., reproduction, growth, adaptations to stress, and metabolism. Each such system involves the hypothalamus, the pituitary, and a specific target gland or organ. In the quantification of the interactions among these components, biostatistical modeling has played an important role. In the present article, five key challenges to an understanding of the interactions of these systems are illustrated and discussed critically.
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Affiliation(s)
- Daniel M Keenan
- Department of Statistics, University of Virginia, Charlottesville, Virginia; and
| | - Johannes D Veldhuis
- Department of Medicine, Endocrine Research Unit, Mayo School of Graduate Medical Education, Clinical Translational Science Center, Mayo Clinic, Rochester, Minnesota
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Rao A, Steels E, Inder WJ, Abraham S, Vitetta L. Testofen, a specialised Trigonella foenum-graecum seed extract reduces age-related symptoms of androgen decrease, increases testosterone levels and improves sexual function in healthy aging males in a double-blind randomised clinical study. Aging Male 2016; 19:134-42. [PMID: 26791805 DOI: 10.3109/13685538.2015.1135323] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
This study examined the effect of Testofen, a specialised Trigonella foenum-graecum seed extract on the symptoms of possible androgen deficiency, sexual function and serum androgen concentrations in healthy aging males. This was a double-blind, randomised, placebo-controlled trial involving 120 healthy men aged between 43 and 70 years of age. The active treatment was standardised Trigonella foenum-graecum seed extract at a dose of 600 mg/day for 12 weeks. The primary outcome measure was the change in the Aging Male Symptom questionnaire (AMS), a measure of possible androgen deficiency symptoms; secondary outcome measures were sexual function and serum testosterone. There was a significant decrease in AMS score over time and between the active and placebo groups. Sexual function improved, including number of morning erections and frequency of sexual activity. Both total serum testosterone and free testosterone increased compared to placebo after 12 weeks of active treatment. Trigonella foenum-graecum seed extract is a safe and effective treatment for reducing symptoms of possible androgen deficiency, improves sexual function and increases serum testosterone in healthy middle-aged and older men.
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Affiliation(s)
- Amanda Rao
- a Department of Medicine , University of Sydney , Sydney , Australia
| | - Elizabeth Steels
- b Integrated Health Group, Clinical Research , Brisbane , Australia
| | - Warrick J Inder
- c Department of Diabetes and Endocrinology , Princess Alexandra Hospital , Brisbane , Australia , and
| | - Suzanne Abraham
- a Department of Medicine , University of Sydney , Sydney , Australia
| | - Luis Vitetta
- a Department of Medicine , University of Sydney , Sydney , Australia
- d Medlab Pty Ltd , Sydney , Australia
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Veldhuis J, Yang R, Roelfsema F, Takahashi P. Proinflammatory Cytokine Infusion Attenuates LH's Feedforward on Testosterone Secretion: Modulation by Age. J Clin Endocrinol Metab 2016; 101:539-49. [PMID: 26600270 PMCID: PMC4880122 DOI: 10.1210/jc.2015-3611] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
CONTEXT In the experimental animal, inflammatory signals quench LH's feedforward drive of testosterone (T) secretion and appear to impair GnRH-LH output. The degree to which such suppressive effects operate in the human is not known. OBJECTIVE To test the hypothesis that IL-2 impairs LH's feedforward drive on T and T's feedback inhibition of LH secretion in healthy men. SETTING Mayo Center for Translational Science Activities. PATIENTS OR OTHER PARTICIPANTS A total of 35 healthy men, 17 young and 18 older. INTERVENTIONS Randomized prospective double-blind saline-controlled study of IL-2 infusion in 2 doses with concurrent 10-minute blood sampling for 24 hours. MAIN OUTCOME MEASURES Deconvolution analysis of LH and T secretion. RESULTS After saline injection, older compared with young men exhibited reduced LH feedforward drive on T secretion (P < .001), and decreased T feedback inhibition of LH secretion (P < .01). After IL-2 injection, LH's feedforward onto T secretion declined markedly especially in young subjects (P < .001). Concomitantly, IL-2 potentiated T's proportional feedback on LH secretion especially in older volunteers. CONCLUSION This investigation confirms combined feedforward and feedback deficits in older relative to young men given saline and demonstrates 1) joint mechanisms by which IL-2 enforces biochemical hypogonadism, viz, combined feedforward block and feedback amplification; and 2) unequal absolute inhibition of T and LH secretion by IL-2 in young and older men. These outcomes establish that the male gonadal axis is susceptible to dual-site suppression by a prototypic inflammatory mediator. Thus, we postulate that selected ILs might also enforce male hypogonadism in chronic systemic inflammation.
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Affiliation(s)
- Johannes Veldhuis
- Endocrine Research Unit (J.V., R.Y.), Mayo Clinic College of Medicine, Center for Translational Science Activities, and Primary Care Internal Medicine (P.T.), Mayo Clinic, Rochester, Minnesota 55905; and Leiden University Medical Center (F.R.), 2333ZA Leiden, The Netherlands
| | - Rebecca Yang
- Endocrine Research Unit (J.V., R.Y.), Mayo Clinic College of Medicine, Center for Translational Science Activities, and Primary Care Internal Medicine (P.T.), Mayo Clinic, Rochester, Minnesota 55905; and Leiden University Medical Center (F.R.), 2333ZA Leiden, The Netherlands
| | - Ferdinand Roelfsema
- Endocrine Research Unit (J.V., R.Y.), Mayo Clinic College of Medicine, Center for Translational Science Activities, and Primary Care Internal Medicine (P.T.), Mayo Clinic, Rochester, Minnesota 55905; and Leiden University Medical Center (F.R.), 2333ZA Leiden, The Netherlands
| | - Paul Takahashi
- Endocrine Research Unit (J.V., R.Y.), Mayo Clinic College of Medicine, Center for Translational Science Activities, and Primary Care Internal Medicine (P.T.), Mayo Clinic, Rochester, Minnesota 55905; and Leiden University Medical Center (F.R.), 2333ZA Leiden, The Netherlands
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Abstract
The pituitary gland has a role in puberty, reproduction, stress-adaptive responses, sodium and water balance, uterine contractions, lactation, thyroid function, growth, body composition and skin pigmentation. Ageing is marked by initially subtle erosion of physiological signalling mechanisms, resulting in lower incremental secretory-burst amplitude, more disorderly patterns of pituitary hormone release and blunted 24 h rhythmic secretion. Almost all pituitary hormones are altered by ageing in humans, often in a manner dependent on sex, body composition, stress, comorbidity, intercurrent illness, medication use, physical frailty, caloric intake, immune status, level of exercise, and neurocognitive decline. The aim of this article is to critically discuss the mechanisms mediating clinical facets of changes in the hypothalamic-pituitary axis during ageing, and the extent to which confounding factors operate to obscure ageing-related effects.
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Affiliation(s)
- Johannes D Veldhuis
- Endocrine Research Unit, Mayo School of Graduate Medical Education, Center for Translational Science Activities, Mayo Clinic, Rochester, MN 55905, USA.
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French JA. The role of androgenic steroids in shaping social phenotypes across the lifespan in male marmosets (Callithrix spp.). Am J Primatol 2013; 75:212-21. [PMID: 23335110 PMCID: PMC4036459 DOI: 10.1002/ajp.22077] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2012] [Revised: 07/31/2012] [Accepted: 08/05/2012] [Indexed: 11/09/2022]
Abstract
Steroid hormones, particularly androgens and their metabolic derivatives, play a prominent role in shaping morphological, behavioral, and social phenotypes in many organisms, including primates. This paper reviews the endocrine correlates of development in male marmoset monkeys of the genus Callithrix (C. kuhlii and C. geoffroyi). A lifespan developmental perspective is adopted, in which our knowledge of hormone effects and profiles from prenatal periods through old age is described. Prenatal steroid hormones appear to play a prominent role in shaping behavioral and morphological phenotypes both the prepartum and in the early postpartum periods of life, with exposure to high gestational androgen associated with reduced fetal growth and lower levels of juvenile play. Early postnatal elevations in androgen levels in males are ubiquitous in Callithrix, and play a role in the further differentiation of male genital morphology and behavior. Changes in androgens as males approach puberty are similar to the conventional primate pattern, and unlike in female marmosets, gonadal steroidogenesis appears to be independent of social context. In adults, androgens appear to be an important modulator of paternal responsiveness to infants, since androgens are low at times when males typically engage in maximal levels of care, and fathers that care for offspring extensively appear to have lower androgen levels than fathers that are less involved in offspring care. Finally, aging in male marmosets is associated with reduced androgen levels. This reduction appears to be attributable to deficits in central mechanisms, since experimental induction and inhibition of gonadal steroid synthesis and release appears to be normal in older males. Together, these results suggest a complex picture of lifetime involvement of androgens in shaping marmoset phenotypes.
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Affiliation(s)
- Jeffrey A French
- Department of Psychology, University of Nebraska at Omaha, Omaha, NE 68182, USA.
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Camacho EM, Huhtaniemi IT, O'Neill TW, Finn JD, Pye SR, Lee DM, Tajar A, Bartfai G, Boonen S, Casanueva FF, Forti G, Giwercman A, Han TS, Kula K, Keevil B, Lean ME, Pendleton N, Punab M, Vanderschueren D, Wu FCW. Age-associated changes in hypothalamic-pituitary-testicular function in middle-aged and older men are modified by weight change and lifestyle factors: longitudinal results from the European Male Ageing Study. Eur J Endocrinol 2013; 168:445-55. [PMID: 23425925 DOI: 10.1530/eje-12-0890] [Citation(s) in RCA: 234] [Impact Index Per Article: 21.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
OBJECTIVE Health and lifestyle factors are associated with variations in serum testosterone levels in ageing men. However, it remains unclear how age-related changes in testosterone may be attenuated by lifestyle modifications. The objective was to investigate the longitudinal relationships between changes in health and lifestyle factors with changes in hormones of the reproductive endocrine axis in ageing men. DESIGN A longitudinal survey of 2736 community-dwelling men aged 40-79 years at baseline recruited from eight centres across Europe. Follow-up assessment occurred mean (±S.D.) 4.4±0.3 years later. RESULTS Paired testosterone results were available for 2395 men. Mean (±S.D.) annualised hormone changes were as follows: testosterone -0.1±0.95 nmol/l; free testosterone (FT) -3.83±16.8 pmol/l; sex hormone-binding globulin (SHBG) 0.56±2.5 nmol/l and LH 0.08±0.57 U/l. Weight loss was associated with a proportional increase, and weight gain a proportional decrease, in testosterone and SHBG. FT showed a curvilinear relationship to weight change; only those who gained or lost ≥15% of weight showed a significant change (in the same direction as testosterone). Smoking cessation was associated with a greater decline in testosterone than being a non-smoker, which was unrelated to weight change. Changes in number of comorbid conditions or physical activity were not associated with significant alterations in hypothalamic-pituitary-testicular (HPT) axis function. CONCLUSIONS Body weight and lifestyle factors influence HPT axis function in ageing. Weight loss was associated with a rise, and weight gain a fall, in testosterone, FT and SHBG. Weight management appears to be important in maintaining circulating testosterone in ageing men, and obesity-associated changes in HPT axis hormones are reversible following weight reduction.
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Affiliation(s)
- E M Camacho
- Andrology Research Unit, Institute of Human Development, Centre for Endocrinology and Diabetes, University of Manchester, Old St Mary's Building, Hathersage Road, Manchester M13 9WL, UK
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Zengerling F, Schrader AJ, Cronauer MV, Stemann H, Schrader M, Rinnab L. The "Aging Males' Symptoms" Scale (AMS): predictive value for lowered circulating androgens. Aging Male 2012; 15:253-7. [PMID: 23078021 DOI: 10.3109/13685538.2012.729232] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
BACKGROUND Symptoms of the "male climacteric" are often at least in part referred to an age-dependent decline of serum androgen levels. Therefore, we evaluated the relationship of climacteric symptoms as assessed by the "Aging Males' Symptoms" (AMS) Questionnaire with circulating androgen levels. METHODS 146 ambulatory men (age, 27-85 years) were surveyed with the AMS Questionnaire and sampled for serum values of total testosterone (tT) and sexual hormone binding globulin (SHBG). Free testosterone (fT) was calculated from tT and SHBG. A total AMS score ≥37 was considered pathological; the lower limits for tT and fT were set to 8 nmol/l and 180 pmol/l, respectively. RESULTS A significant deficit in tT and fT was shown in 25 (17.1%) and 34 (24.5%) men, respectively; the AMS Questionnaire showed pathological results for 66 (45.2%) men. In predicting a tT deficit, the AMS Questionnaire rendered a sensitivity of 76% and a specificity of 61.6%, only. However, multiple regression analysis revealed a significant correlation of lowered tT with a pathological somatovegetative and psychological AMS subscore (p = 0.042 and p = 0.01) and a correlation of lowered fT with a pathological sexual subscore (p = 0.039). CONCLUSION In predicting hypogonadism the AMS Questionnaire in total did not render a sufficient diagnostic efficiency.
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Veldhuis JD, Liu PY, Takahashi PY, Weist SM, Wigham JR. Analysis of the impact of intravenous LH pulses versus continuous LH infusion on testosterone secretion during GnRH-receptor blockade. Am J Physiol Regul Integr Comp Physiol 2012; 303:R994-R1002. [PMID: 22992702 DOI: 10.1152/ajpregu.00314.2012] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Gonadotrophin-releasing hormone (GnRH) pulsatility is required for optimal luteinizing hormone (LH) secretion, but whether LH pulsatility is required for physiological testosterone (T) secretion is not known. To test the postulate that pulses of recombinant human (rh) LH stimulate greater T secretion than continuous infusion of the same dose, a potent selective GnRH antagonist was administered overnight to 19 healthy men ages 18-49 yr. Subjects then received saline or rhLH intravenously continuously or as 6-min pulses intravenously every 1 or 2 h at the same total dose. Blood was sampled every 10 min for 10 h to quantify T responses. For the four interventions, the descending rank order of mean LH and mean T concentrations was 1-h = 2-h rhLH pulses > continuous rhLH > saline (P < 10(-3)). Plateau LH and T concentrations correlated positively (R(2) = 0.943, P = 0.029) as did LH concentrations and LH half-lives (R(2) = 0.962, P = 0.019). Percentage pulsatile T secretion assessed by deconvolution analysis (Keenan DM, Takahashi PY, Liu PY, Roebuck PD, Nehra AX, Iranmanesh A, Veldhuis JD. Endocrinology 147: 2817-2828, 2006) was the highest (P = 0.019), and half-time to attain peak T concentrations was the shortest (P < 10(-6)), for 1-h rhLH pulses. Approximate entropy (a pattern-regularity measure) revealed more orderly T secretion for 1- than 2-h rhLH pulses (P = 0.0076). Accordingly, a pulsatile LH signal, while not obligatory to maintain mean T concentrations, controls the mean plasma LH concentration and determines quantifiable patterns of T secretion. These data introduce the question whether blood T patterns in turn supervise distinctive target-tissue responses.
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Affiliation(s)
- Johannes D Veldhuis
- Endocrine Research Unit, Dept. of Internal Medicine, Mayo School of Graduate Medical Education, Center for Translational Science Activities, Mayo Clinic, Rochester, MN 55905, USA.
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Keenan DM, Wang X, Pincus SM, Veldhuis JD. Modeling the Nonlinear Time Dynamics of Multidimensional Hormonal Systems. JOURNAL OF TIME SERIES ANALYSIS 2012; 33:779-796. [PMID: 22977290 PMCID: PMC3437937 DOI: 10.1111/j.1467-9892.2012.00795.x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
In most hormonal systems (as well as many physiological systems more generally), the chemical signals from the brain, which drive much of the dynamics, can not be observed in humans. By the time the molecules reach peripheral blood, they have been so diluted so as to not be assayable. It is not possible to invasively (surgically) measure these agents in the brain. This creates a difficult situation in terms of assessing whether or not the dynamics may have changed due to disease or aging. Moreover, most biological feedforward and feedback interactions occur after time delays, and the time delays need to be properly estimated. We address the following two questions: (1) Is it possible to devise a combination of clinical experiments by which, via exogenous inputs, the hormonal system can be perturbed to new steady-states in such a way that information about the unobserved components can be ascertained; and, (2) Can one devise methods to estimate (possibly, time-varying) time delays between components of a multidimensional nonlinear time series, which are more robust than traditional methods? We present methods for both questions, using the Stress (ACTH-cortisol) hormonal system as a prototype, but the approach is more broadly applicable.
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Affiliation(s)
- Daniel M Keenan
- Department of Statistics, University of Virginia, Charlottesville, Va 22904
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Antonopoulou M, Sharma R, Farag A, Banerji MA, Karam JG. Hypopituitarism in the elderly. Maturitas 2012; 72:277-85. [PMID: 22727068 DOI: 10.1016/j.maturitas.2012.05.002] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2012] [Accepted: 05/06/2012] [Indexed: 11/25/2022]
Abstract
Pituitary dysfunction in elderly can represent a true diagnostic and therapeutic challenge to clinicians caring for these patients. Symptoms associated with partial or total hypopituitarism, such as fatigue, lower muscle strength and decreased libido, are nonspecific and can be often attributed to normal aging. Gold standard pituitary diagnostic testing carries higher risks in elderly and is classically replaced by alternative testing. Furthermore, the benefits and safety of selective pituitary hormonal replacement, specifically sexual and growth hormone replacement, remain subject of controversy in this group of patients. Recognizing and appropriately treating hypopituitarism in elderly is crucial for the survival and well being of the older patients with this disease.
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Keenan DM, Clarke IJ, Veldhuis JD. Noninvasive analytical estimation of endogenous GnRH drive: analysis using graded competitive GnRH-receptor antagonism and a calibrating pulse of exogenous GnRH. Endocrinology 2011; 152:4882-93. [PMID: 22028450 PMCID: PMC3230048 DOI: 10.1210/en.2011-1461] [Citation(s) in RCA: 15] [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
Homeostatic control of endocrine systems proceeds via feedforward (agonistic, stimulatory) and feedback (antagonistic, inhibitory) interactions mediated via implicit dose-response functions. However, neither the feedback/feedforward pathways nor the dose-response interfaces are directly observed in vivo. Thus, the goal was to formulate and estimate an ensemble construct of time-varying feedback/feedforward interactions among GnRH, LH, and testosterone (T) in the male gonadal axis. The new analytical model revises and extends an earlier construct by: 1) allowing systemic T concentrations to inhibit hypothalamic GnRH output; 2) estimating GnRH outflow after injection of a calibrating pulse of biosynthetic GnRH; 3) framing the pituitary response to GnRH as a secretory burst, rather than continuous LH release; and 4) regressing feedback and feedforward ensemble parameters on age, rather than evaluating age dichotomously. Application of this methodology in 21 men aged 23-72 yr unveiled age-related 1) diminution of GnRH efficacy normalized for the decline in free T with age (P = 0.016), 2) potentiation of maximal T feedback onto (inhibition of) GnRH secretion (P = 0.006), and 3) accentuation of hypothalamic GnRH's sensitivity to T repression (P = 0.003). Outcomes were specific, because injected GnRH agonist and antagonist concentrations were invariant of age. We conclude that combining experimental and analytical strategies may provide a noninvasive means to investigate and decipher feedback determinants of unobserved endocrine signal(s).
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Affiliation(s)
- Daniel M Keenan
- Department of Statistics, University of Virginia, Charlottesville, Virginia 22904, USA
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Keenan DM, Iranmanesh A, Veldhuis JD. Analytical construct of reversible desensitization of pituitary-testicular signaling: illustrative application in aging. Am J Physiol Regul Integr Comp Physiol 2010; 300:R349-60. [PMID: 21084679 DOI: 10.1152/ajpregu.00477.2010] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Luteinizing hormone (LH) administered in pharmacological amounts downregulates Leydig cell steroidogenesis. Whether reversible downregulation of physiological gonadotropin drive operates in vivo is unknown. Most of the analytical models of dose-response functions that have been constructed are biased by the assumption that no downregulation exists. The present study employs a new analytical platform to quantify potential (but not required) pulsatile cycles of LH-testosterone (T) dose-response stimulation, desensitization, and recovery (pulse-by-pulse hysteresis) in 26 healthy men sampled every 10 min for 24 h. A sensitivity-downregulation hysteresis construct predicted marked hysteresis with a median time delay to LH dose-response inflection within individual T pulses of 23 min and with median T pulse onset and recovery LH sensitivities of 1.1 and 0.10 slope unit, respectively (P < 0.001). A potency-downregulation model yielded median estimates of one-half maximally stimulatory LH concentrations (EC(50) values) of 0.66 and 7.5 IU/l for onset and recovery, respectively (P < 0.001). An efficacy-downregulation formulation of hysteresis forecasts median LH efficacies of 20 and 8.3 ng·dl(-1)·min(-1) for onset and offset of T secretory burst, respectively (P = 0.002). Segmentation of the LH-T data by age suggested greater sensitivity, higher EC(50) (increased LH potency), and markedly (2.7-fold) attenuated LH efficacy in older individuals. Each of the three hysteresis models yielded a marked (P < 0.005) reduction in estimated model residual error compared with no hysteresis. In summary, model-based analyses allowing for (but not requiring) reversible pituitary-gonadal effector-response downregulation are consistent with a hypothesis of recurrent, brief cycles of LH-dependent stimulation, desensitization, and recovery of pulsatile T secretion in vivo and an age-associated reduction of LH efficacy. Prospective studies would be required to prove this aging effect.
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Affiliation(s)
- Daniel M Keenan
- Department of Statistics, University of Virginia, Charlottesville, USA
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Iranmanesh A, Mulligan T, Veldhuis JD. Age in men does not determine gonadotropin-releasing hormone's dose-dependent stimulation of luteinizing hormone secretion under an exogenous testosterone clamp. J Clin Endocrinol Metab 2010; 95:2877-84. [PMID: 20357176 PMCID: PMC2902075 DOI: 10.1210/jc.2009-2581] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
BACKGROUND Aging is associated with a decline in incremental LH pulse amplitude, which could be due to decreased GnRH secretion or impaired GnRH action. HYPOTHESIS Inconsistent published studies of GnRH action in older men may be due to disparate sex-steroid milieus. FACILITY This study was conducted at a clinical translational-research unit. SUBJECTS We studied 16 healthy men (8 young men and 8 older men). METHODS An overnight transdermal testosterone (T) clamp was implemented before randomly ordered injections of 0, 2.5, 10, 25, 250, and 750 ng GnRH on separate days (96 study sessions). OUTCOMES LH responses were quantified by variable-waveform deconvolution analysis. RESULTS The T clamp maintained age-invariant mean concentrations of total, bioavailable, and free T, SHBG, LH, FSH, and prolactin. By two-way analysis of covariance, GnRH dose (P < 0.001) but not age (0.15 < or = P < or = 0.83) determined mean, peak, incremental, and pulsatile LH responses. Statistical power (median) was 95, 98, 90, and 99% to detect a 30% or greater age contrast at P < or = 0.05 in mean, peak, incremental, and pulsatile LH responses, and greater than 99% to detect a 30% or greater age contrast in bioavailable or total T concentrations. Higher GnRH doses (P < 0.001) abbreviated LH secretory bursts in both age groups. CONCLUSION In the face of eugonadal concentrations of total, bioavailable, and free T, young and older men exhibit remarkably similar LH responses to a 300-fold dose range of exogenous GnRH. Accordingly, previously reported disparate effects of age on GnRH action may reflect in part age-discrepant sex-steroid milieus.
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Affiliation(s)
- Ali Iranmanesh
- Endocrine Section, Department of Medicine, Salem Veterans Affairs Medical Center, Salem, Virginia 24153, USA
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Vitzthum VJ, Worthman CM, Beall CM, Thornburg J, Vargas E, Villena M, Soria R, Caceres E, Spielvogel H. Seasonal and circadian variation in salivary testosterone in rural Bolivian men. Am J Hum Biol 2010; 21:762-8. [PMID: 19367574 DOI: 10.1002/ajhb.20927] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
Testosterone (T) plays a key role in the increase and maintenance of muscle mass and bone density in adult men. Life history theory predicts that environmental stress may prompt a reallocation of such investments to those functions critical to survival. We tested this hypothesis in two studies of rural Bolivian adult men by comparing free T levels and circadian rhythms during late winter, which is especially severe, to those in less arduous seasons. For each pair of salivary T(AM)/T(PM) samples (collected in a approximately 12-h period), circadian rhythm was considered classic (C(CLASSIC)) if T(AM) > 110%T(PM), reverse (C(REVERSE)) if T(PM) > 110%T(AM), and flat (C(FLAT)) otherwise. We tested the hypotheses that mean T(AM) > mean T(PM) and that mean T(LW) < mean T(OTHER) (LW = late winter, OTHER = other seasons). In Study A, of 115 T(PM)-T(AM) pairs, 51% = C(CLASSIC), 39% = C(REVERSE), 10% = C(FLAT); in Study B, of 184 T(AM)-T(PM) pairs, 55% = C(CLASSIC), 33% = C(REVERSE), 12% = C(FLAT). Based on fitting linear mixed models, in both studies T(OTHER-AM) > T(OTHER-PM) (A: P = 0.035, B: P = 0.0005) and T(OTHER-AM) > T(LW-AM) (A: P = 0.054, B: P = 0.007); T(PM) did not vary seasonally, and T diurnality was not significant during late winter. T diurnality varied substantially between days within an individual, between individuals and between seasons, but neither T levels nor diurnality varied with age. These patterns may reflect the seasonally varying but unscheduled, life-long, strenuous physical labor that typifies many non-industrialized economies. These results also suggest that single morning samples may substantially underestimate peak circulating T for an individual and, most importantly, that exogenous signals may moderate diurnality and the trajectory of age-related change in the male gonadal axis.
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Affiliation(s)
- Virginia J Vitzthum
- Anthropology Department and Kinsey Institute for Research in Sex, Gender & Reproduction, Indiana University, Bloomington, Indiana 47405, USA.
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Veldhuis JD, Keenan DM, Pincus SM. Regulation of Complex Pulsatile and Rhythmic Neuroendocrine Systems: the Male Gonadal Axis as a Prototype. PROGRESS IN BRAIN RESEARCH 2010; 181:79-110. [DOI: 10.1016/s0079-6123(08)81006-0] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
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Keenan DM, Veldhuis JD. Age-dependent regression analysis of male gonadal axis. Am J Physiol Regul Integr Comp Physiol 2009; 297:R1215-27. [PMID: 19587110 PMCID: PMC2777776 DOI: 10.1152/ajpregu.90800.2008] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2008] [Accepted: 07/02/2009] [Indexed: 11/22/2022]
Abstract
The mechanisms by which aging progressively depletes testosterone (Te) availability in the male are unknown. Accordingly, the objective was to estimate brain gonadotropin-releasing hormone (GnRH) outflow (release and action), which cannot be observed directly, on the basis of downstream effects on pituitary luteinizing hormone (LH) secretion. LH, in turn, feeds forward on (stimulates) gonadal Te secretion, which then feeds back on (inhibits) GnRH-driven LH secretion. LH and Te concentrations were measured repetitively (every 10 min) over 18 h during graded pharmacological blockade of endogenous GnRH outflow in 24 healthy 20- to 72-yr-old men. Data were analyzed using a new age-dependent regression model of GnRH-LH-Te interactions to estimate pulsatile LH secretion and elimination, GnRH outflow, LH feedforward, and Te feedback. By incorporating regression on age within the dose-response model, we show that aging erodes all three primary forward and reverse pathways linking the brain, pituitary gland, and testes. Aging is associated with concomitant deficits in GnRH --> LH feedforward, LH --> Te feedforward, and Te --> GnRH/LH feedback. The analytical formalism should be generalizable to other ensemble regulatory systems, such as those that control growth, reproduction, stress adaptations, and glucose metabolism.
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Affiliation(s)
- Daniel M Keenan
- Department of Statistics, University of Virginia, Charlottesville, Virginia, USA
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Liu PY, Takahashi PY, Roebuck PD, Bailey JN, Keenan DM, Veldhuis JD. Testosterone's short-term positive effect on luteinizing-hormone secretory-burst mass and its negative effect on secretory-burst frequency are attenuated in middle-aged men. J Clin Endocrinol Metab 2009; 94:3978-86. [PMID: 19584190 PMCID: PMC2758726 DOI: 10.1210/jc.2009-0135] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
BACKGROUND Testosterone (T) production declines and LH pulses become smaller and more frequent in middle-aged men. The mechanisms underlying these changes are not known. RATIONALE Small frequent LH pulses in middle-aged men could reflect impaired feedback by systemic T. HYPOTHESIS Middle age disrupts negative feedback by T on selected facets of LH secretion. SUBJECTS AND SETTING Healthy men were studied at an academic medical center. METHODS The protocol comprised blockade of gonadal steroidogenesis and graded transdermal addback of T doses of 0, 2.5, 5, or 7.5 mg/d designed to span the castrate to physiological range of T concentrations in each of 23 healthy men ages 19-71 yr (interquartile range, 28-53 yr). We quantified 12-h basal and pulsatile LH secretion (92 time series) using a mathematically justified deconvolution method. RESULTS Stepwise T supplementation from the hypogonadal through the eugonadal range repressed mean (12-h) LH concentrations (P = 0.001). By regression analysis, age attenuated the capabilities of increasing T concentrations to 1) increase LH secretory-burst mass (P < 0.0001); and 2) decrease LH secretory-burst frequency (P = 0.025). Age did not alter T's feedback on basal LH secretion, interpulse regularity, the waveform of LH secretory bursts, or the slow half-life of LH. CONCLUSION Middle age impairs both the positive and negative actions of systemic T on pulsatile LH secretion in healthy men, thus potentially explaining earlier inconsistencies in feedback studies based upon single-sample mean LH concentrations. Longitudinal studies will be required to elucidate the precise age dependence of inferred dual feedback failure.
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Affiliation(s)
- Peter Y Liu
- Endocrine Research Unit, Mayo Medical School, Mayo School of Graduate Medical Education, Center for Translational Science Activities, Mayo Clinic, Rochester, Minnesota 55905, USA
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Keenan DM, Alexander S, Irvine C, Veldhuis JD. Quantifying nonlinear interactions within the hypothalamo-pituitary-adrenal axis in the conscious horse. Endocrinology 2009; 150:1941-51. [PMID: 19022882 PMCID: PMC2659283 DOI: 10.1210/en.2008-1249] [Citation(s) in RCA: 18] [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
Cortisol is an important mediator of physiological stress responses. Hypothalamic CRH and arginine vasopressin (AVP) and pituitary ACTH, in addition to hypothalamic and pituitary cortisol feedback, regulate cortisol secretion. Importantly, joint interactions among the four, rather than the signal of any one hormone, govern this life-preserving axis. Quantifying in vivo strength of such joint interactions has been difficult, especially without direct injection of cortisol, CRH, AVP, or ACTH. The goal of the present research was to estimate these joint feedback and feedforward interactions in vivo in the conscious horse during low-cortisol and hypoglycemic stress. Pituitary venous sampling of ACTH, CRH, and AVP was performed every 0.5-1 min and jugular venous sampling of cortisol every 15-20 min. Estimation of hypothalamic dynamics revealed that: 1) hypocortisolemia amplifies CRH and AVP secretion, when mean (slow) and rate-adjusted (rapid) cortisol feedback concentrations decrease by 0-25%; and 2) reduced peptide feedback augments CRH and AVP secretion, when CRH and AVP secretion each decreases by 0-25 and 50% of its respective maximum. Thus, low-cortisol feedback enhances CRH outflow in part by relieving CRH's autoinhibition. Estimation of pituitary dynamics disclosed that: 1) endogenous CRH and AVP synergize in evoking ACTH secretion, and 2) hypocortisolemia potentiates individual and conjoint stimulation of ACTH secretion by CRH and AVP. Formulations such as the present one should have application to evaluating other complex endocrine dynamics.
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Affiliation(s)
- Daniel M Keenan
- Department of Statistics, University of Virginia, Charlottesville, Virginia 22904, USA
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Veldhuis JD, Keenan DM, Liu PY, Iranmanesh A, Takahashi PY, Nehra AX. The aging male hypothalamic-pituitary-gonadal axis: pulsatility and feedback. Mol Cell Endocrinol 2009; 299:14-22. [PMID: 18838102 PMCID: PMC2662347 DOI: 10.1016/j.mce.2008.09.005] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/24/2007] [Revised: 09/02/2008] [Accepted: 09/04/2008] [Indexed: 11/29/2022]
Abstract
Aging results in insidious decremental changes in hypothalamic, pituitary and gonadal function. The foregoing three main anatomic loci of control are regulated by intermittent time-delayed signal exchange, principally via gonadotropin-releasing hormone (GnRH), luteinizing hormone (LH) and testosterone/estradiol (Te/E(2)). A mathematical framework is required to embody these dynamics. The present review highlights integrative adaptations in the aging male hypothalamic-pituitary-gonadal axis, as assessed by recent objective ensemble models of the axis as a whole.
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Affiliation(s)
- Johannes D Veldhuis
- Endocrine Research Unit, Department of Internal Medicine, Mayo Clinic College of Medicine, Mayo Clinic, 200 First Steet SW, Rochester, MN 55905, United States.
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Veldhuis JD, Keenan DM, Pincus SM. Motivations and methods for analyzing pulsatile hormone secretion. Endocr Rev 2008; 29:823-64. [PMID: 18940916 PMCID: PMC2647703 DOI: 10.1210/er.2008-0005] [Citation(s) in RCA: 156] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/20/2008] [Accepted: 09/16/2008] [Indexed: 01/05/2023]
Abstract
Endocrine glands communicate with remote target cells via a mixture of continuous and intermittent signal exchange. Continuous signaling allows slowly varying control, whereas intermittency permits large rapid adjustments. The control systems that mediate such homeostatic corrections operate in a species-, gender-, age-, and context-selective fashion. Significant progress has been made in understanding mechanisms of adaptive interglandular signaling in vivo. Principal goals are to understand the physiological origins, significance, and mechanisms of pulsatile hormone secretion. Key analytical issues are: 1) to quantify the number, size, shape, and uniformity of pulses, nonpulsatile (basal) secretion, and elimination kinetics; 2) to evaluate regulation of the axis as a whole; and 3) to reconstruct dose-response interactions without disrupting hormone connections. This review will focus on the motivations driving and the methodologies used for such analyses.
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Affiliation(s)
- Johannes D Veldhuis
- Endocrine Research Unit, Department of Internal Medicine, Mayo Medical School, Mayo School of Graduate Medical Education, Center for Translational Science Activities, Mayo Clinic, Rochester, Minnesota 55905, USA.
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Veldhuis JD, Keenan DM. Secretagogues govern GH secretory-burst waveform and mass in healthy eugonadal and short-term hypogonadal men. Eur J Endocrinol 2008; 159:547-54. [PMID: 18703567 PMCID: PMC2680123 DOI: 10.1530/eje-08-0414] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
BACKGROUND GH pulses are putatively initiated by hypothalamic GH-releasing hormone (GHRH), amplified by GH-releasing peptide (GHRP), and inhibited by somatostatin (SS). OBJECTIVE To ascertain how secretagogues control the waveform (time evolution of release rates) as well as the mass of secretory bursts. DESIGN We quantified the shape of GH secretory bursts evoked by continuous combined i.v. infusion of maximally effective doses of GHRH and GHRP-2, and by bolus injection of each peptide after delivering L-arginine to restrain hypothalamic SS release in 12 healthy young men. METHODS A mathematically verified and experimentally validated variable-waveform deconvolution model was applied to intensively sampled GH time series. RESULTS The secretory-burst mode (time from burst onset to maximal secretion) was 19+/-0.69 min during saline infusion, and fell to a) 10.4+/-3.0 min during constant dual stimulation with GHRH/GHRP-2 (P<0.01), b) 14.6+/-1.8 min after l-arginine/GHRH (P<0.025), and c) 15.0+/-1.0 min after l-arginine/GHRH (P<0.01). Secretagogues augmented the mass of GH secreted in pulses by 44-, 42-, and 16-fold respectively, over saline (2.2+/-0.81 microg/l per h; P<0.001 for each). Pulse number and variability were unaffected. Applying the same methodology to ten other young men with acute leuprolide-induced hypogonadism yielded comparable waveform and mass estimates. CONCLUSION The present analyses in men demonstrate that peptidyl secretagogues modulate not only the magnitude but also the time course of the GH-release process in vivo independently of the short-term sex-steroid milieu.
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Affiliation(s)
- Johannes D Veldhuis
- Endocrine Research Unit, Mayo Medical and Graduate Schools, Mayo Clinic, Rochester, Minnesota 55905, USA.
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Kok P, Roelfsema F, Frölich M, van Pelt J, Meinders AE, Pijl H. Short-term treatment with bromocriptine improves impaired circadian growth hormone secretion in obese premenopausal women. J Clin Endocrinol Metab 2008; 93:3455-61. [PMID: 18559918 DOI: 10.1210/jc.2008-0001] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
CONTEXT A profound reduction of spontaneous as well as stimulated GH secretion has been consistently observed in obesity. Dopamine promotes GH release through activation of dopamine D2 receptors (D2Rs). Dopamine D2R availability in the brain is reduced in obese humans in proportion to body adiposity. We hypothesized that impaired dopamine D2R signaling is mechanistically involved in the deficient GH secretion associated with obesity. OBJECTIVE To test this hypothesis, we studied the effect of short-term bromocriptine (B) (a D2R agonist) treatment on spontaneous 24-h GH secretion in obese women, while body weight and caloric intake remained constant. DESIGN This was a prospective, fixed order, cross-over study. SETTING The study was performed in the Clinical Research Center at Leiden University Medical Center. PARTICIPANTS There were 18 healthy obese women (body mass index 33.2 +/- 0.6 kg/m2) studied twice in the early follicular phase of their menstrual cycle. INTERVENTION(S) Eight days of treatment with B and placebo (Pl) was performed. MAIN OUTCOME MEASURE(S) Blood was collected during 24 h at 10-min intervals for determination of GH concentrations. GH secretion parameters were calculated using deconvolution analysis. RESULTS Short-term treatment with B significantly enhanced diurnal GH secretion (Pl 121.4 +/- 16.4 vs. B 155.4 +/- 15.2 microg/liter(volume of distribution).24 h; P = 0.01), whereas IGF-I concentrations remained constant (Pl 22.4 +/- 2.4 vs. B 21.8 +/- 1.6 nmol/liter; P = 0.928). CONCLUSIONS Activation of dopamine D2Rs by B favorably affects impaired nyctohemeral GH secretion in obese women. Reduced dopaminergic neuronal signaling might be involved in the pathogenesis of obesity associated hyposomatotropism.
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Affiliation(s)
- Petra Kok
- Department of General Internal Medicine, Leiden University Medical Center, RC Leiden, The Netherlands
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Wu FCW, Tajar A, Pye SR, Silman AJ, Finn JD, O'Neill TW, Bartfai G, Casanueva F, Forti G, Giwercman A, Huhtaniemi IT, Kula K, Punab M, Boonen S, Vanderschueren D. Hypothalamic-pituitary-testicular axis disruptions in older men are differentially linked to age and modifiable risk factors: the European Male Aging Study. J Clin Endocrinol Metab 2008; 93:2737-45. [PMID: 18270261 DOI: 10.1210/jc.2007-1972] [Citation(s) in RCA: 586] [Impact Index Per Article: 36.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
CONTEXT The cause of declining testosterone (T) in aging men and their relationships with risk factors are unclear. OBJECTIVE The objective of the study was to investigate the relationships between lifestyle and health with reproductive hormones in aging men. DESIGN This was a baseline cross-sectional survey on 3200 community-dwelling men aged 40-79 yr from a prospective cohort study in eight European countries. RESULTS Four predictors were associated with distinct modes of altered function: 1) age: lower free T (FT; -3.12 pmol/liter.yr, P < 0.001) with raised LH, suggesting impaired testicular function; 2) obesity: lower total T (TT; -2.32 nmol/liter) and FT (-17.60 pmol/liter) for body mass index (BMI; > or = 25 to < 30 kg/m(2)) and lower TT (-5.09 nmol/liter) and FT (-53.72 pmol/liter) for BMI 30 kg/m(2) or greater (P < 0.001-0.01, referent: BMI < 25 kg/m(2)) with unchanged/decreased LH, indicating hypothalamus/pituitary dysfunction; 3) comorbidity: lower TT (-0.80 nmol/liter, P < 0.01) with unchanged LH in younger men but higher LH in older men; and 4) smoking: higher SHBG (5.96 nmol/liter, P < 0.001) and LH (0.77 U/liter, P < 0.01) with increased TT (1.31 nmol/liter, P < 0.001) but not FT, compatible with a resetting of T-LH-negative feedback due to elevated SHBG. CONCLUSIONS Complex multiple alterations in the hypothalamic-pituitary-testicular axis function exist in aging men against a background of progressive age-related testicular impairment. These changes are differentially linked to specific risk factors. Some risk factors operate independently of but others interact with age, in contributing to the T decline. These potentially modifiable risk factors suggest possible preventative measures to maintain T during aging in men.
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Affiliation(s)
- Frederick C W Wu
- Department of Endocrinology, Manchester Royal Infirmary, Oxford Road, Manchester, United Kingdom.
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Veldhuis JD. Aging and hormones of the hypothalamo-pituitary axis: gonadotropic axis in men and somatotropic axes in men and women. Ageing Res Rev 2008; 7:189-208. [PMID: 18343203 DOI: 10.1016/j.arr.2007.12.005] [Citation(s) in RCA: 66] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2007] [Revised: 12/18/2007] [Accepted: 12/19/2007] [Indexed: 10/22/2022]
Abstract
Neuroendocrinology of the aging (male) gonadal and (male and female) somatotropic axes will be reviewed. A companion chapter discusses reproductive hormonal changes in aging women. Both the gonadal and growth-hormone/insulin-like growth factor (GH/IGF-I) axes function as ensembles. The ensembles comprise tripartite interactions among the brain (hypothalamus), anterior pituitary gland (gonadotrope and somatotrope cells) and target organs (testis, liver, muscle, fat and brain). Compelling evidence indicates that combined hypothalamic and gonadal adaptations operate in the reproductive axis of older men, and multiple hypothalamic adaptations prevail in the GH axis of elderly men and women. Evolving investigative methods allow more precise parsing of the particular mechanisms that subserve such age-related changes, and suggest novel interventional strategies to evaluate the physiological impact of the dynamic alterations discerned in aging individuals.
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Aksglaede L, Jensen RB, Carlsen E, Kok P, Keenan DM, Veldhuis J, Skakkebaek NE, Juul A. Increased basal and pulsatile secretion of FSH and LH in young men with 47,XXY or 46,XX karyotypes. Eur J Endocrinol 2008; 158:803-10. [PMID: 18322303 PMCID: PMC2729082 DOI: 10.1530/eje-07-0709] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
OBJECTIVE The regulation of normal sexual maturation and reproductive function is dependent on a precise hormonal regulation at hypothalamic, pituitary, and gonadal levels. The aim of this study was to investigate the neuroendocrine integrity of the pituitary-gonadal axis in patients with primary testicular failure due to supernumerary X chromosomes. DESIGN Cross-sectional study. METHODS In this study, 7 untreated patients with primary gonadal insufficiency due to SRY-positive 46,XX (n=4) and 46,XXY karyotypes (n=3) aged 18.8 years and 25 age-matched healthy controls participated. Reproductive hormones, testicular size, and overnight LH and FSH serum profiles and overnight urine LH and FSH excretion were determined. RESULTS Basal LH and FSH secretion was elevated 6.3- and 25.4-fold respectively in the patients and the amount of LH and FSH secreted per burst were 2.0- and 6.6-fold elevated. We found significantly more LH but not FSH peaks per 24 h, as estimated by the Weibull lambda analysis. There was no difference between approximate entropy ratios or Weibull gamma analyses indicating comparable orderliness and regularity of LH and FSH secretion. Overnight urinary LH and FSH excretion was significantly elevated in patients compared with controls and correlated significantly with calculated total overnight LH and FSH secretion respectively, thus validating deconvolution. CONCLUSION In this group of patients with severe hypergonadotropic hypogonadism due to a supernumerary X chromosome, higher basal, pulsatile, and total LH and FSH secretion were associated with significantly more LH peaks per 24 h in comparison with healthy controls. Thus, our data indicate that in patients with Klinefelter syndrome and XX male karyotypes the entire hypothalamic-pituitary-gonadal axis has undergone functional changes.
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Affiliation(s)
- Lise Aksglaede
- University Department of Growth and Reproduction GR, Rigshospitalet, University of Copenhagen, Section 5064, Blegdamsvej 9, DK-2100 Copenhagen Ø, Denmark.
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Abstract
Androgens can increase muscular mass and strength and remain the most frequently abused and widely available drugs used in sports doping. Banning the administration of natural or synthetic androgens has led to a variety of strategies to circumvent the ban of the most effective ergogenic agents for power sports. Among these, a variety of indirect androgen doping strategies aiming to produce a sustained rise in endogenous testosterone have been utilized. These include oestrogen blockade by drugs that act as oestrogen receptor antagonists (antioestrogen) or aromatase inhibitors. The physiological and pharmacological basis for the effects of oestrogen blockade in men, but not women, are reviewed.
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Schlatt S, Pohl CR, Ehmcke J, Ramaswamy S. Age-related changes in diurnal rhythms and levels of gonadotropins, testosterone, and inhibin B in male rhesus monkeys (Macaca mulatta). Biol Reprod 2008; 79:93-9. [PMID: 18367678 DOI: 10.1095/biolreprod.107.066126] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/01/2022] Open
Abstract
Testosterone shows circadian rhythms in monkeys with low serum levels in the morning hours. The decline relies on a diminished frequency of LH pulses. Inhibin B shows no diurnal patterns. In elderly men, the diurnal rhythm of testosterone is blunted and inhibin levels fall. Here we explore whether aging exerts similar effects in the rhesus monkey. We collected blood samples from groups of young (6-9 yr) and old (12-16 yr) male rhesus monkeys at 20-min intervals for a period of 24 h under remote sampling via a venous catheter. We determined moment-to-moment changes in plasma levels of testosterone, FSH, and LH by RIA, and of inhibin B by ELISA. We found significant diurnal patterns of testosterone in both groups. The circadian rhythm in testosterone was enhanced in older monkeys. Testosterone levels and pulse frequencies dropped significantly below those of young monkeys during midday hours. Diminished pulse frequency of LH appeared to be responsible for the midday testosterone decrease in old monkeys, while LH and testosterone pulse frequency did not change in young monkeys at corresponding time points. Old monkeys showed extended periods of LH-pulse quiescence in the morning and midday hours. Inhibin B and FSH levels were generally lower in old monkeys compared with the young group, but neither inhibin B nor FSH showed circadian rhythms. We conclude from these data that old rhesus monkeys have a more prominent circadian rhythm of LH and testosterone resulting from an extended midday period of quiescence in the hypothalamus-pituitary-gonadal axis.
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Affiliation(s)
- Stefan Schlatt
- Department of Cell Biology and Physiology, Center for Research in Reproductive Physiology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261, USA.
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Natesampillai S, Kerkvliet J, Leung PCK, Veldhuis JD. Regulation of Kruppel-like factor 4, 9, and 13 genes and the steroidogenic genes LDLR, StAR, and CYP11A in ovarian granulosa cells. Am J Physiol Endocrinol Metab 2008; 294:E385-91. [PMID: 18056793 PMCID: PMC2747322 DOI: 10.1152/ajpendo.00480.2007] [Citation(s) in RCA: 30] [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] [Indexed: 12/19/2022]
Abstract
Kruppel-like factors (KLFs) are important Sp1-like eukaryotic transcriptional proteins. The LDLR, StAR, and CYP11A genes exhibit GC-rich Sp1-like sites, which have the potential to bind KLFs in multiprotein complexes. We now report that KLF4, KLF9, and KLF13 transcripts are expressed in and regulate ovarian cells. KLF4 and 13, but not KLF9, mRNA expression was induced and then repressed over time (P < 0.001). Combined LH and IGF-I stimulation increased KLF4 mRNA at 2 h (P < 0.01), whereas LH decreased KLF13 mRNA at 6 h (P < 0.05), and IGF-I reduced KLF13 at 24 h (P < 0.01) compared with untreated control. KLF9 was not regulated by either hormone. Transient transfection of KLF4, KLF9, and KLF13 suppressed LDLR/luc, StAR/luc, and CYP11A/luc by 80-90% (P < 0.001). Histone-deacetylase (HDAC) inhibitors stimulated LDLR/luc five- to sixfold and StAR/luc and CYP11A/luc activity twofold (P < 0.001) and partially reversed suppression by all three KLFs (P < 0.001). Deletion of the zinc finger domain of KLF13 abrogated repression of LDLR/luc. Lentiviral overexpression of the KLF13 gene suppressed LDLR mRNA (P < 0.001) and CYP11A mRNA (P = 0.003) but increased StAR mRNA (P = 0.007). Collectively, these data suggest that KLFs may recruit inhibitory complexes containing HDAC corepressors, thereby repressing LDLR and CYP11A transcription. Conversely, KLF13 may recruit unknown coactivators or stabilize StAR mRNA, thereby explaining enhancement of in situ StAR gene expression. These data introduce new potent gonadal transregulators of genes encoding proteins that mediate sterol uptake and steroid biosynthesis.
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Affiliation(s)
- Sekar Natesampillai
- Endocrine Research Unit, Department of Internal Medicine, Mayo Clinic School of Medicine, Rochester, MN, United States, 55901
| | - Jason Kerkvliet
- Endocrine Research Unit, Department of Internal Medicine, Mayo Clinic School of Medicine, Rochester, MN, United States, 55901
| | - Peter C. K. Leung
- Department of Obstetrics and Gynecology, University of British Columbia, Vancouver, British Columbia, Canada
| | - Johannes D. Veldhuis
- Endocrine Research Unit, Department of Internal Medicine, Mayo Clinic School of Medicine, Rochester, MN, United States, 55901
- Corresponding author: Tel: (507) 255-0906, Fax: (507) 255-0901,
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Iranmanesh A, Carpenter PC, Mielke K, Bowers CY, Veldhuis JD. Putative somatostatin suppression potentiates adrenocorticotropin secretion driven by ghrelin and human corticotropin-releasing hormone. J Clin Endocrinol Metab 2007; 92:3653-9. [PMID: 17566099 DOI: 10.1210/jc.2007-0523] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
CONTEXT Ghrelin is a 28-amino-acid Ser(3)-octanoylated peptide, and CRH is a 41-amino-acid peptide, both of which stimulate ACTH secretion. In principle, actions of these agonists could be subject to inhibitory modulation by hypothalamic somatostatin (SS). OBJECTIVE Our objective was to test the hypothesis that endogenous SS restrains ghrelin and CRH-stimulated ACTH secretion, thereby linking all three, ghrelin, CRH, and SS, with ACTH secretion. DESIGN AND SETTING We conducted a randomized, double-blind, placebo-controlled, crossover interventional study at an academic medical center. PARTICIPANTS Ten healthy postmenopausal women participated in the study. INTERVENTIONS Interventions included iv injection of saline, ghrelin, human CRH, or both after an infusion of saline vs. l-arginine to putatively inhibit SS outflow (eight visits per subject). OUTCOME MEASURES ACTH concentrations quantified by repetitive blood sampling and immunochemiluminometry. RESULTS Infusion of ghrelin induced peak ACTH concentrations [median (range)] of 21 (17-28) compared with 16 (11-20) ng/liter after saline (P = 0.037). CRH and l-arginine infusion evoked ACTH peaks of 23 (14-48) and 31 (21-286) ng/liter, respectively (P = 0.037 and P = 0.005 vs. saline). l-Arginine enhanced stimulation by ghrelin by 1.43-fold (P = 0.028) and that by CRH by 1.91-fold (P = 0.005). Triple stimulation with ghrelin, CRH, and l-arginine potentiated the effect of combined ghrelin/CRH by 1.45-fold (P = 0.028). Downstream cortisol responses mimicked those of ACTH but were time delayed. CONCLUSIONS The present outcomes indicate that the peptide ensemble comprising ghrelin, CRH, and SS (inferred by l-arginine infusion) can regulate ACTH and cortisol secretion in healthy adults.
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Affiliation(s)
- Ali Iranmanesh
- Endocrine Section, Department of Medicine, Salem Veterans Affairs Medical Center, Salem, Virginia 24153, USA
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Takahashi PY, Votruba P, Abu-Rub M, Mielke K, Veldhuis JD. Age attenuates testosterone secretion driven by amplitude-varying pulses of recombinant human luteinizing hormone during acute gonadotrope inhibition in healthy men. J Clin Endocrinol Metab 2007; 92:3626-32. [PMID: 17579202 DOI: 10.1210/jc.2006-2704] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/12/2023]
Abstract
CONTEXT Whether testosterone (Te) depletion in aging men reflects deficits in the testis, hypothalamus, and/or pituitary gland is unknown. OBJECTIVE Our objective was to quantify the impact of age on gonadal Te secretion driven by amplitude-varying pulses of recombinant human LH (rhLH) in the absence of confounding by endogenous hypothalamo-pituitary signals. DESIGN This was a double-blind, placebo-controlled study. SETTING The setting was an academic medical center. SUBJECTS Fifteen healthy community-dwelling men ages 22-78 yr were included in the study. INTERVENTION Saline or four separate rhLH doses were each infused twice iv in randomized order as one pulse every 2 h over 20 h to stimulate Te secretion, after LH secretion was suppressed by a GnRH-receptor antagonist, ganirelix. MAIN OUTCOME LH and Te concentrations were determined in blood samples collected every 5 min. Maximal and minimal (as well as mean) Te responses were regressed linearly on age to reflect LH peak and nadir (and average) effects, respectively. RESULTS The ganirelix/rhLH paradigm yielded serum LH concentrations of 4.6 +/- 0.22 IU/liter (normal range 1-9). By regression analysis, age was associated with declines in rhLH pulse-stimulated peak and nadir (and mean) concentrations of total Te (P = 0.0068), bioavailable Te (P = 0.0096), and free Te (P = 0.013), as well as lower Te/LH concentration ratios (P < 0.005). Deconvolution analysis suggested that the half-life of infused LH increases by 12%/decade (P = 0.044; R(2) = 0.28). CONCLUSIONS Infusion of amplitude-varying pulses of rhLH during gonadal-axis suppression in healthy men unmasks prominent age-related deficits in stimulated total (39%), bioavailable (66%), and free (63%) Te concentrations, and a smaller age-associated increase in LH half-life. These data suggest that age-associated factors reduce the efficacy of LH pulses.
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Affiliation(s)
- Paul Y Takahashi
- Endocrine Research Unit, Department of Internal Medicine, General Clinical Research Center, Mayo Medical and Graduate Schools of Medicine, Mayo Clinic, Rochester, Minnesota 55905, USA
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Farhy LS, Bowers CY, Veldhuis JD. Model-projected mechanistic bases for sex differences in growth hormone regulation in humans. Am J Physiol Regul Integr Comp Physiol 2007; 292:R1577-93. [PMID: 17185408 DOI: 10.1152/ajpregu.00584.2006] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Models of physiological systems facilitate rational experimental design, inference, and prediction. A recent construct of regulated growth hormone (GH) secretion interlinks the actions of GH-releasing hormone (GHRH), somatostatin (SRIF), and GH secretagogues (GHS) with GH feedback in the rat (Farhy LS, Veldhuis JD. Am J Physiol Regul Integr Comp Physiol 288: R1649–R1663, 2005). In contrast, no comparable formalism exists to explicate GH dynamics in any other species. The present analyses explore whether a unifying model structure can represent species- and sex-defined distinctions in the human and rodent. The consensus principle that GHRH and GHS synergize in vivo but not in vitro was explicable by assuming that GHS 1) evokes GHRH release from the brain, 2) opposes inhibition by SRIF both in the hypothalamus and on the pituitary gland, and 3) stimulates pituitary GH release directly and additively with GHRH. The gender-selective principle that GH pulses are larger and more irregular in women than men was conferrable by way of 4) higher GHRH potency and 5) greater GHS efficacy. The overall construct predicts GHRH/GHS synergy in the human only in the presence of SRIF when the brain-pituitary nexus is intact, larger and more irregular GH pulses in women, and observed gender differences in feedback by GH and the single and paired actions of GHRH, GHS, and SRIF. The proposed model platform should enhance the framing and interpretation of novel clinical hypotheses and create a basis for interspecies generalization of GH-axis regulation.
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Affiliation(s)
- Leon S Farhy
- Division of Endocrinology and Metabolism, Department of Internal Medicine, School of Medicine, University of Virginia, Charlottesville, Virginia, USA
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Abstract
Ageing of the male reproductive system is characterized by changes in the endocrine system, hypogonadism, erectile dysfunction and proliferative disorders of the prostate gland. Stochastic damage accumulating within ageing leads to progressive dysregulation at each level of the hypothalamic-pituitary-gonadal (HPG) axis and in local auto/paracrine interactions, thereby inducing morphological changes in reproductive target organs, such as the prostate, testis and penis. Despite age-related changes in the HPG axis, endocrine functions are generally sufficient to maintain fertility in elderly men. Ageing of the male reproductive system can give rise to clinically relevant manifestations, such as benign prostatic hyperplasia (BPH), prostate cancer (PCa) and erectile dysfunction (ED). In this review, we discuss morphological/histological changes occurring in these organs and current views and concepts of the underlying pathology. Moreover, we emphasize the molecular/cellular pathways leading to reduced testicular/penile function and proliferative disorders of the prostate gland.
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Affiliation(s)
- N Sampson
- Institute for Biomedical Ageing Research, Austrian Academy of Sciences, Innsbruck, Austria
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Haren MT, Kim MJ, Tariq SH, Wittert GA, Morley JE. Andropause: a quality-of-life issue in older males. Med Clin North Am 2006; 90:1005-23. [PMID: 16962854 DOI: 10.1016/j.mcna.2006.06.001] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Testosterone deficiency occurs commonly in men as they grow older. This deficiency often is associated with a decline in sexual activity and a loss of muscle mass. Testosterone replacement can reverse many of these effects. At present, no ideal form of testosterone replacement is available. Like the phosphodiesterase-5 inhibitors, testosterone replacement in older men is a quality of life issue.
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Affiliation(s)
- Matthew T Haren
- Division of Geriatric Medicine, Saint Louis University School of Medicine, 1402 South Grand Boulevard, M238, MO 63104, USA
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Veldhuis JD, Keenan DM, Iranmanesh A, Mielke K, Miles JM, Bowers CY. Estradiol potentiates ghrelin-stimulated pulsatile growth hormone secretion in postmenopausal women. J Clin Endocrinol Metab 2006; 91:3559-65. [PMID: 16804038 DOI: 10.1210/jc.2006-0948] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
CONTEXT Ghrelin and an estrogen-rich milieu individually amplify pulsatile GH secretion by increasing the amount of hormone released per burst. However, how these distinct agonists interact in controlling pulsatile GH output is not known. OBJECTIVE The objective of the study was to test the hypothesis that elevated estradiol (E(2)) concentrations potentiate hypothalamo-pituitary responses to a near-physiological ghrelin stimulus. DESIGN This was a double-blind, placebo-controlled, prospectively randomized, parallel-cohort study. SETTING The study was conducted at an academic medical center. SUBJECTS Twenty-one postmenopausal women participated in the study. INTERVENTIONS Eleven subjects received placebo (Pl) and 10 others E(2) transdermally in escalating doses over 3 wk to mimic late follicular-phase E(2) concentrations. Saline or a submaximally stimulatory amount of ghrelin (0.3 microg/kg) was infused iv on separate randomly ordered mornings fasting after 17-21 d of Pl or E(2) administration. OUTCOMES Outcomes included serum concentrations of E(2), ghrelin, GH, IGF-I, IGF binding protein (IGFBP)-1 and IGFBP-3, and the estimated mass and waveform of stimulated GH secretory bursts. RESULTS Administration of E(2) yielded late follicular-phase E(2) concentrations. Compared with Pl, E(2) did not alter ghrelin concentrations but reduced IGF-I and IGFBP-3 and elevated IGFBP-1 concentrations. Compared with saline, ghrelin infusion amplified pulsatile GH secretion by 7.1-fold (P < 0.01). The effect of E(2) alone was 2.0-fold placebo and that of combined ghrelin/E(2) 10.4-fold (P < 0.01). Ghrelin and E(2) accelerated initial GH release individually but nonadditively by more than 2-fold (P < 0.01). CONCLUSIONS Estrogen augments ghrelin's near-physiological stimulation of pulsatile GH secretion and mimics ghrelin's acceleration of initial GH release. Thus, we hypothesize that estrogen and a GH secretagogue act via independent as well as convergent mechanisms.
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Affiliation(s)
- Johannes D Veldhuis
- Endocrine Research Unit, Department of Internal Medicine, Mayo School of Graduate Medical Education, General Clinical Research Center, Mayo Clinic, Rochester, Minnesota 55905, USA.
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