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van der Spoel E, Roelfsema F, van Heemst D. Relationships Between 24-hour LH and Testosterone Concentrations and With Other Pituitary Hormones in Healthy Older Men. J Endocr Soc 2021; 5:bvab075. [PMID: 34337275 PMCID: PMC8315483 DOI: 10.1210/jendso/bvab075] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/16/2021] [Indexed: 12/04/2022] Open
Abstract
Objective To investigate the relationship between LH and testosterone (T), which characteristics associate with the strength of this relationship, and their interrelationships with GH, TSH, cortisol, and ACTH. Design Hormones were measured in serum samples collected every 10 minutes during 24 hours from 20 healthy men, comprising 10 offspring of long-lived families and 10 control subjects, with a mean (SD) age of 65.6 (5.3) years. We performed cross-correlation analyses to assess the relative strength between 2 timeseries for all possible time shifts. Results Mean (95% CI) maximal correlation was 0.21 (0.10-0.31) at lag time of 60 minutes between LH and total T concentrations. Results were comparable for calculated free, bioavailable, or secretion rates of T. Men with strong LH-T cross-correlations had, compared with men with no cross-correlation, lower fat mass (18.5 [14.9-19.7] vs. 22.3 [18.4-29.4] kg), waist circumference (93.6 [5.7] vs. 103.1 [12.0] cm), high-sensitivity C-reactive protein (0.7 [0.4-1.3] vs. 1.8 [0.8-12.3] mg/L), IL-6 (0.8 [0.6-1.0] vs. 1.2 [0.9-3.0] pg/mL), and 24-hour mean LH (4.3 [2.0] vs. 6.1 [1.5] U/L), and stronger LH-T feedforward synchrony (1.5 [0.3] vs. 1.9 [0.2]). Furthermore, T was positively cross-correlated with TSH (0.32 [0.21-0.43]), cortisol (0.26 [0.19-0.33]), and ACTH (0.26 [0.19-0.32]). Conclusions LH is followed by T with a delay of 60 minutes in healthy older men. Men with a strong LH-T relationship had more favorable body composition, inflammatory markers, LH levels, and LH-T feedforward synchrony. We observed positive correlations between T and TSH, cortisol, and ACTH.
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Affiliation(s)
- Evie van der Spoel
- Section Gerontology and Geriatrics, Department of Internal Medicine, Leiden University Medical Center, Leiden, The Netherlands
| | - Ferdinand Roelfsema
- Section Endocrinology, Department of Internal Medicine, Leiden University Medical Center, Leiden, The Netherlands
| | - Diana van Heemst
- Section Gerontology and Geriatrics, Department of Internal Medicine, Leiden University Medical Center, Leiden, The Netherlands
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2
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Hao E, Chang LY, Wang DH, Chen YF, Huang RI, Chen H. Dietary Supplementation with Ferula Improves Productive Performance, Serum Levels of Reproductive Hormones, and Reproductive Gene Expression in Aged Laying Hens. BRAZILIAN JOURNAL OF POULTRY SCIENCE 2021. [DOI: 10.1590/1806-9061-2020-1319] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Affiliation(s)
- E Hao
- Hebei Agricultural University, China
| | - LY Chang
- Hebei Agricultural University, China
| | - DH Wang
- Hebei Agricultural University, China
| | - YF Chen
- Hebei Agricultural University, China
| | - RI Huang
- Hebei Agricultural University, China
| | - H Chen
- Hebei Agricultural University, China
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3
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The relationship between the mTOR signaling pathway and ovarian aging in peak-phase and late-phase laying hens. Poult Sci 2020; 100:334-347. [PMID: 33357698 PMCID: PMC7772700 DOI: 10.1016/j.psj.2020.10.005] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2020] [Revised: 08/21/2020] [Accepted: 10/06/2020] [Indexed: 11/23/2022] Open
Abstract
The molecular mechanisms underlying reproductive aging in avian species are poorly understood. Previous studies have shown the importance of mechanistic target of rapamycin (mTOR) signaling pathway in aging. In this study, we investigated the relationship between the mTOR signaling pathway and ovarian aging in the peak phase and late phase of egg production in laying hens. The egg production rate and egg quality were tracked for 5 consecutive weeks in 30-week-old and 70-week-old Dawu Jinfeng hens (N = 30/group). During the peak phase (week 35) and late phase (week 75), antioxidant and immune indicators were detected by enzyme-linked immunosorbent assay, and mTOR signaling-related genes (CLIP-170, GRB10, LIPIN-1, ATG1, 4E-BP1, S6K, PKC, RHO, and SGK1) were detected in the follicles by quantitative reverse transcription-PCR technology. The protein expression of key genes (mTOR, PKC, 4EBP1) was evaluated by Western blot analysis. The egg production rate and the antioxidant indexes superoxide dismutase and glutathione peroxidase and the levels of total antioxidant capacity and immunoglobulins (IgM and IgG) were significantly higher at week 35 than those at week 75 (P < 0.01), while malondialdehyde levels were significantly lower (P < 0.01). At week 75, there were fewer follicles in the different stages of development than were detected at week 35. The number of white follicles (large and small) and primary follicles were significantly higher at week 75 than those detected at week 35 (P < 0.01). The mRNA expression of avTOR, CLIP-170, GRB10, LIPIN-1, 4E-BP1, S6K, RHO, and SGK genes in small white follicles (SWF), large white follicles (LWF), F3, F1, and ovary at week 75 was lower than that in the hens at week 35 (P < 0.05). The mRNA expression in small yellow follicle (SYF) was significantly higher than that at week 35 (P < 0.05), while the mRNA expression of ULK1 in SWF, LWF, F3, F1, and ovary at week 75 was higher than that of hens at week 35 (P<0.01), and SYF was lower (P < 0.05). Treatment of chicken granulosa cells with the mTOR agonist MHY1485 significantly enhanced granulocyte proliferation (P < 0.01) and inhibited apoptosis (P < 0.01) and significantly increased avTOR, S6K, 4E-BP1, and PKC gene expression (P < 0.01). The protein expression levels of mTOR, S6K, p-mTOR, and p-S6K were consistent with mRNA expression levels. The mTOR activity is age-specific, and a compensatory enhancement of the mTOR signaling cascade can regulate ovarian follicular development in aged laying hens.
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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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Taghvafard H, Proskurnikov AV, Cao M. An impulsive model of endocrine regulation with two negative feedback loops * *The work was supported in part by the European Research Council (ERC-StG-307207). ACTA ACUST UNITED AC 2017. [DOI: 10.1016/j.ifacol.2017.08.2508] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Chen H, Guo J, Ge R, Lian Q, Papadopoulos V, Zirkin BR. Steroidogenic fate of the Leydig cells that repopulate the testes of young and aged Brown Norway rats after elimination of the preexisting Leydig cells. Exp Gerontol 2015; 72:8-15. [PMID: 26335619 DOI: 10.1016/j.exger.2015.08.014] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2015] [Revised: 08/20/2015] [Accepted: 08/25/2015] [Indexed: 10/23/2022]
Abstract
The capacity of Brown Norway rat Leydig cells to produce testosterone (T) decreases with aging. In a previous study, we reported that a new generation of Leydig cells can be restored in both young and old rat testes after a single injection of ethane dimethanesulfonate (EDS), and that the abilities of the new Leydig cells in young and old rats to produce T were equivalent. Our objective herein was to compare the steroidogenic fate of the new Leydig cells over time. Young (3 month-old) and old (18 month-old) rats were injected with EDS to eliminate the existing Leydig cells. Ten weeks after EDS, Leydig cells had been restored and T production by the new Leydig cells isolated from young and old rat testes was equivalent. Thirty weeks after EDS treatment of young rats, the ability of the new Leydig cells to produce T had not diminished from 10 weeks post-EDS. In contrast, at 30 weeks post-EDS, T production by new cells in old rat testes was reduced significantly from the 10-week level. Serum T levels at 10 and 30 weeks were consistent with Leydig cell T production. Serum LH levels did not differ in any group. Thus, although the Leydig cells restored to both young and old rats after EDS initially produced T at high, equivalent levels, the cells in the old testes did not maintain this ability. These results suggest that: 1) the cells from which new populations of Leydig cells are derived may differ depending upon the age of the rat; and/or 2) factors extrinsic to the new Leydig cells in young and old testes differ, and it is these differences that are responsible for reductions in T by the newly formed Leydig cells in the testes of old rats.
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Affiliation(s)
- Haolin Chen
- The Second Affiliated Hospital, Wenzhou Medical University, Wenzhou, Zhejiang, China; Department of Biochemistry and Molecular Biology, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD, USA.
| | - Jingjing Guo
- The Second Affiliated Hospital, Wenzhou Medical University, Wenzhou, Zhejiang, China
| | - Renshan Ge
- The Second Affiliated Hospital, Wenzhou Medical University, Wenzhou, Zhejiang, China
| | - Qingquan Lian
- The Second Affiliated Hospital, Wenzhou Medical University, Wenzhou, Zhejiang, China
| | - Vassilios Papadopoulos
- The Research Institute of the McGill University Health Centre, Montreal, Canada; Department of Medicine, McGill University, Montreal, Canada; Department of Biochemistry, McGill University, Montreal, Canada; Department of Pharmacology & Therapeutics, McGill University, Montreal, Canada
| | - Barry R Zirkin
- Department of Biochemistry and Molecular Biology, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD, USA
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7
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Niu S, Kou S, Zhou X, Ding L. Heshouwu decoction, a Chinese herb for tonifying kidney, ameliorates hypothalamic-pituitary- testicular axis secretion in aging rats. Neural Regen Res 2015; 7:1611-7. [PMID: 25657700 PMCID: PMC4308762 DOI: 10.3969/j.issn.1673-5374.2012.21.002] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2012] [Accepted: 05/13/2012] [Indexed: 01/16/2023] Open
Abstract
An increasing amount of evidence demonstrates the anti-aging effect of Heshouwu in pill form. In this study, a subacute aging rat model was established by continuous intraperitoneal injection of D-galactose and treated with Heshouwu decoction (a Chinese herb for tonifying the kidney, comprising Heshouwu pill, Herba Epimedii, Radix Salviae Miltiorrhiae, and Poria). Heshouwu pill treated rats were the positive control group. Radioimmunoassay, immunohistochemical staining, and western blot assay showed hypothalamic gonadotropin-releasing hormone, hypothalamic substance P, and serum gonadotropin levels to be significantly increased in the model rats; the concentrations of hypothalamic β-endorphin, and serum levels of insulin-like growth factor 1 and testosterone were significantly decreased. 17β- and 3β-hydroxysteroid dehydrogenase expression in testicular tissue was also decreased. Intragastric administration of Heshouwu decoction at high (9.6 g/mL/100 g), medium (4.8 g/mL/100 g), and low (2.4 g/mL/100 g) doses, Heshouwu decoction pretreatment at a medium dose (4.8 g/mL/100 g), and Heshouwu pill (2.06 g/mL/100 g) significantly reversed these changes. Heshouwu decoction pretreatment and high-dose Heshouwu decoction had the greatest anti-aging effects. These experimental findings indicate that Heshouwu decoction can improve hypothalamic-pituitary-testicular axis secretion in a subacute aging rat model, and prevent and delay gonadal axis aging, with an effect superior to that of Heshouwu pill.
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Affiliation(s)
- Siyun Niu
- School of Basic Medical Science, Hebei University, Baoding 071000, Hebei Province, China
| | - Suru Kou
- School of Basic Medical Science, Hebei University, Baoding 071000, Hebei Province, China
| | - Xiaochun Zhou
- Institute of Basic Medical Sciences, Chengde Medical College, Chengde 067000, Hebei Province, China
| | - Liang Ding
- School of Basic Medical Science, Hebei University, Baoding 071000, Hebei Province, China
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8
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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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9
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Trumble BC, Brindle E, Kupsik M, O'Connor KA. Responsiveness of the reproductive axis to a single missed evening meal in young adult males. Am J Hum Biol 2011; 22:775-81. [PMID: 20721980 DOI: 10.1002/ajhb.21079] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
OBJECTIVES The male reproductive axis is responsive to energetic deficits, including multiday fasts, but little is known about brief periods of fasting (<24 hours). Reduced testosterone in low-energy balance situations is hypothesized to reflect redirection of resources from reproduction to survival. This study tests the hypothesis that testosterone levels decrease during a minor caloric deficiency by assessing the effects of a single missed (evening) meal on morning testosterone in 23 healthy male participants, age 19-36. METHODS Participants provided daily saliva and urine samples for two baseline days and the morning following an evening fast (water only after 4 PM). Testosterone, cortisol, and luteinizing hormone were measured with enzyme immunoassays. RESULTS Fasting specimens had significantly lower overnight urinary luteinizing hormone (P = 0.045) and morning salivary testosterone than baseline (P = 0.037). In contrast to morning salivary testosterone, there was a significant increase in overnight urinary testosterone (P = 0.000) following the evening fast, suggesting an increase in urinary clearance rates. There was a marginal increase in overnight urinary cortisol (P = 0.100), but not morning salivary cortisol (P = 0.589). CONCLUSION These results suggest the male reproductive axis may react more quickly to energetic imbalances than has been previously appreciated.
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Affiliation(s)
- Benjamin C Trumble
- Department of Anthropology, University of Washington, Seattle, Washington 98195, USA.
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10
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Abstract
BACKGROUND Endocrine feedback control networks are typically complex and contain multiple hormones, pools, and compartments. The hormones themselves commonly interact via multiple pathways and targets within the networks, and a complete description of such relationships may involve hundreds of parameters. In addition, it is often difficult, if not impossible, to collect experimental data pertaining to every component within the network. Therefore, the complete simultaneous analysis of such networks is challenging. Nevertheless, an understanding of these networks is critical for furthering our knowledge of hormonal regulation in both physiologic and pathophysiologic conditions. METHODS We propose a novel approach for the analysis of dose-response relationships of subsets of hormonal feedback networks. The algorithm and signal-response quantification (SRQuant) software is based on convolution integrals, and tests whether several discretely measured input signals can be individually delayed, spread in time, transformed, combined, and discretely convolved with an elimination function to predict the time course of the concentration of an output hormone. Signal-response quantification is applied to examples from the endocrine literature to demonstrate its applicability to the analysis of the different endocrine networks. RESULTS In one example, SRQuant determines the dose-response relationship by which one hormone regulates another, highlighting its advantages over other traditional methods. In a second example, for the first time (to the best of our knowledge), we show that the secretion of glucagon may be jointly controlled by the β and the δ cells. CONCLUSION We have developed a novel convolution integral-based approach, algorithm, and software (SRQuant) for the analysis of dose-response relationships within subsets of complex endocrine feedback control networks.
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Affiliation(s)
- Michael L Johnson
- Department of Pharmacology, Center for Biomathematical Technology, University of Virginia, Charlottesville, Virginia 22908-0735, USA.
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11
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Liu PY, Pincus SM, Takahashi PY, Roebuck PD, Iranmanesh A, Keenan DM, Veldhuis JD. Aging attenuates both the regularity and joint synchrony of LH and testosterone secretion in normal men: analyses via a model of graded GnRH receptor blockade. Am J Physiol Endocrinol Metab 2006; 290:E34-E41. [PMID: 16339924 DOI: 10.1152/ajpendo.00227.2005] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Testosterone (T) secretion declines in the aging male, albeit for unknown reasons. From an ensemble perspective, repeated incremental signaling among gonadotropin-releasing hormone (GnRH), luteinizing hormone (LH), and T is required to maintain physiological androgen availability. Pattern-regularity statistics, such as univariate approximate entropy (ApEn) and bivariate cross-ApEn, provide specific and sensitive model-free measurement of altered multi-pathway control. The present study exploits partial muting of one pathway (GnRH drive) to appraise adaptive regulation of LH and T secretion in young and aging individuals. Analyses comprised 100 paired 18-h LH and T concentration time series obtained in 25 healthy men ages 20-72 yr each administered placebo and three graded doses of a specific GnRH-receptor antagonist. Graded blockade of GnRH drive increased the individual regularity of LH and T secretion and the synchrony of LH-T feedforward and T-LH feedback in the cohort as a whole (P<0.001 for each). However, age markedly attenuated ganirelix-induced enhancement of univariate T orderliness and bivariate LH-T feedback and T-LH feedback synchrony (P <or= 0.0025). In summary, the present analyses support the thesis that aging disrupts coordinate control of T secretion, LH-T feedforward, and T-LH feedback in healthy men. Thus the experimental strategy of stepwise silencing of an agonistic pathway may have utility in dissecting the bases of altered neurohormonal linkages in other systems.
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Affiliation(s)
- Peter Y Liu
- Endocrine Research Unit, Dept. of Internal Medicine, Mayo School of Graduate Medical Education, General Clinical Research Center, Mayo Clinic, Rochester, MN 55905, USA
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12
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Liu PY, Takahashi PY, Roebuck PD, Iranmanesh A, Veldhuis JD. Age-specific changes in the regulation of LH-dependent testosterone secretion: assessing responsiveness to varying endogenous gonadotropin output in normal men. Am J Physiol Regul Integr Comp Physiol 2005; 289:R721-8. [PMID: 15890794 DOI: 10.1152/ajpregu.00138.2005] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Pulsatile and thus total testosterone (Te) secretion declines in older men, albeit for unknown reasons. Analytical models forecast that aging may reduce the capability of endogenous luteinizing hormone (LH) pulses to stimulate Leydig cell steroidogenesis. This notion has been difficult to test experimentally. The present study used graded doses of a selective gonadotropin releasing hormone (GnRH)-receptor antagonist to yield four distinct strata of pulsatile LH release in each of 18 healthy men ages 23-72 yr. Deconvolution analysis was applied to frequently sampled LH and Te concentration time series to quantitate pulsatile Te secretion over a 16-h interval. Log-linear regression was used to relate pulsatile LH secretion to attendant pulsatile Te secretion (LH-Te drive) across the four stepwise interventions in each subject. Linear regression of the 18 individual estimates of LH-Te feedforward dose-response slopes on age disclosed a strongly negative relationship (r = -0.721, P < 0.001). Accordingly, the present data support the thesis that aging in healthy men attenuates amplitude-dependent LH drive of burst-like Te secretion. The experimental strategy of graded suppression of neuroglandular outflow may have utility in estimating dose-response adaptations in other endocrine systems.
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Affiliation(s)
- Peter Y Liu
- Endocrine Research Unit, Dept. of Internal Medicine, Mayo School of Graduate Medical Education, General Clinical Research Center, Mayo Clinic, Rochester, MN 55905, USA
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13
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Veldhuis JD, Iranmanesh A, Mulligan T. Age and testosterone feedback jointly control the dose-dependent actions of gonadotropin-releasing hormone in healthy men. J Clin Endocrinol Metab 2005; 90:302-9. [PMID: 15494457 PMCID: PMC1201433 DOI: 10.1210/jc.2004-1313] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Healthy older men manifest combined declines in testosterone concentrations, LH secretory burst mass (amount of LH released per pulse), and feedback-sensitive regularity of unknown cause. To test a unifying hypothesis of simultaneous reductions in GnRH outflow, gonadotrope responsiveness to GnRH, and androgenic negative feedback, we monitored LH secretion 1) after bolus iv injection of a 1000-fold range of randomly ordered individual doses of GnRH on separate mornings, 2) during unmodified (eugonadal) or testosterone-withdrawn (hypoandrogenemic) negative feedback, and 3) in 16 young (age, 18-35 yr) and 15 older (age, 60-85 yr) healthy men. LH secretory burst mass and pattern regularity were quantitated by intensive blood sampling, high specificity LH beta-subunit-directed immunoradiometric assay, deconvolution analysis, and approximate entropy. GnRH dose responsiveness was assessed by four-parameter nonlinear regression analysis. We demonstrated that older men exhibit 1) delayed attainment of GnRH-evoked maximal LH secretion; 2) enhanced potency of GnRH stimulation in both the feedback-intact and feedback-withdrawn states; 3) elevated gonadotrope sensitivity to GnRH, unmasked by experimental testosterone depletion; 4) comparable young adult-like GnRH efficacy, independent of testosterone feedback milieu; and 5) diminished regularity of GnRH-induced LH release evident only during unmodified androgenic feedback. We conclude that a 3-fold interaction among GnRH dose, testosterone concentration, and age governs GnRH action, and age determines both testosterone-modulated and testosterone-independent actions of GnRH.
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Affiliation(s)
- Johannes D Veldhuis
- Division of Endocrinology and Metabolism, Mayo School of Graduate Medical Education, General Clinical Research Center, Mayo Clinic, Rochester, Minnesota 55905, USA.
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Keenan DM, Veldhuis JD. Divergent gonadotropin-gonadal dose-responsive coupling in healthy young and aging men. Am J Physiol Regul Integr Comp Physiol 2004; 286:R381-9. [PMID: 14592930 DOI: 10.1152/ajpregu.00376.2003] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The present study extends a recent composite model of in vivo interglandular signaling to assess the impact of age on 1) nonequilibrium exchange among diffusible and protein-bound testosterone (Te); 2) elimination of total and free Te; 3) basal and pulsatile Te secretion (sec); 4) the implicit feedforward function mediating luteinizing hormone (LH) concentration (con) drive of instantaneous Te sec; and 5) possible stochastic variability of the predicted LH con-Te sec dose-response linkage. To this end, we measured LH and Te con every 10 min for 24 h in healthy young ( n = 13) and older men ( n = 13). Statistical comparisons of analytic estimates revealed that elderly subjects manifest 1) reduced maximal burstlike LH-stimulated Te sec (impaired stimulus efficacy); 2) depressed half-maximally LH-stimulated Te sec (lower Leydig-cell responsivity); 3) decreased pulsatile and total Te sec; 4) elevated basal Te sec; 5) a prolonged half-life of total but not free Te con; and 6) delayed time evolution of LH and Te sec bursts. In contradistinction, age did not influence estimated LH-pulse potency (ED50), steroidogenic sensitivity (slope term), or stochastic variability of LH-Te coupling. On the basis of these data, we postulate that aging in the human male alters specific dose-response attributes linking LH con and Te sec and disrupts the time waveform of LH and Te sec bursts.
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Affiliation(s)
- Daniel M Keenan
- Division of Endocrinology and Metabolism, Dept. of Internal Medicine, Mayo Medical and Graduate Schools of Medicine, Mayo Clinic, 200 First St. SW, Rochester, MN 55905, USA
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Keenan DM, Veldhuis JD. Hypothesis testing of the aging male gonadal axis via a biomathematical construct. Am J Physiol Regul Integr Comp Physiol 2001; 280:R1755-71. [PMID: 11353681 DOI: 10.1152/ajpregu.2001.280.6.r1755] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Neuroendocrine axes are feedback- and feedforward-coupled dynamic ensembles. Disruption of selected pathways in such networklike organizations may explicate loss of orderly hormonal output as observed in aging. To test this notion more explicitly, we implemented an earlier computer-assisted biomathematical model of the interlinked male hypothalamo [gonadotropin-releasing hormone (GnRH)]-pituitary [luteinizing hormone, (LH)]-testicular [Leydig cell testosterone (Te)] axis ( Am J Physiol Endocrinol Metab Physiol 275: E157–E176, 1988; Keenan D., W. Sun, and J. D. Veldhuis, SIAM J Appl Math 61: 934–965, 2000). Thereby, we appraise mechanistic hypotheses for more disorderly LH and Te secretion in aging men. We compare model predictions with monitored abnormalities in the older male, namely, irregular patterns of individual and synchronous LH and Te release, reduced 24-h rhythmic Te output, and variably elevated LH secretion. Among the mechanisms examined, the most parsimonious aging hypothesis would entail impaired LH feedforward on Te without or with attenuated Te feedback on GnRH/LH secretion. This investigative strategy should aid in exploring new postulates of disrupted feedback networks in pathophysiology.
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Affiliation(s)
- D M Keenan
- Department of Statistics, University of Virginia, Charlottesville, Virginia 22903, USA
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Veldhuis JD, Straume M, Iranmanesh A, Mulligan T, Jaffe C, Barkan A, Johnson ML, Pincus S. Secretory process regularity monitors neuroendocrine feedback and feedforward signaling strength in humans. Am J Physiol Regul Integr Comp Physiol 2001; 280:R721-9. [PMID: 11171650 DOI: 10.1152/ajpregu.2001.280.3.r721] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The present experiments examine the neuroregulatory hypothesis that the degree of sample-by-sample regularity of hormone output by an interlinked hypothalamopituitary target-organ system monitors the strength of feedback and/or feedforward signaling. To test this postulate and assess its generality, we implemented a total of nine thematically complementary perturbation experiments. In particular, we altered feedback or feedforward signaling selectively in two distinct neuroendocrine systems; namely, the growth hormone (GH) insulin-like growth factor type I (IGF-I) and the luteinizing hormone-testosterone axes. Four experimental paradigms comprised preferential reduction vs. enhancement of IGF-I or testosterone feedback signal strength; and, conversely, five others entailed selective attenuation vs. augmentation of GH-releasing hormone and gonadotropin-releasing hormone feedforward signal intensity. In these independent interventions, quantitation of subordinate (nonpulsatile) secretory pattern reproducibility via the approximate entropy statistic unmasked salient changes (P values typically <10(-3)) in the conditional regularity of serial hormone output with high consistency (96-100%). In particular, approximate entropy quantified degradation of secretory subpattern orderliness under either muted feedback restraint or heightened feedforward drive. Assuming valid interpretation of the biological constraints imposed, these experimental observations coincide with earlier reductionist mathematical predictions, wherein increased irregularity of coupled parameter output mirrors attenuated feedback and/or augmented feedforward coupling within an integrative system.
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Affiliation(s)
- J D Veldhuis
- Division of Endocrinology, Department of Internal Medicine, General Clinical Research Center, Center for Biomathematical Technology, University of Virginia School of Medicine, Charlottesville, Virginia 22908-0202, USA.
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