| HOME | HELP | CONTACT US | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
Department of Cell Biology and Physiology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261, USA
1 School of Health Sciences, Duquesne University, Pittsburgh, Pennsylvania 15282, USA
2 Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261, USA
(Requests for offprints should be addressed to T Plant; Email: plant1{at}pitt.edu)
 |
Abstract |
|---|
 Top Abstract IntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
|
Introduction |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
In higher primates, the characteristic pulsatile mode of testicular testosterone secretion in the adult is preceded by a protracted phase of quiescence in the hypothalamic–pituitary–gonadal (HPG) axis that is initiated in late infancy and maintained until puberty (Plant 1994). During the hypogonadotropic juvenile phase, however, an adult pattern of testosterone secretion may be elicited by prematurely activating a pubertal pattern of endogenous gonadotropin release (Plant et al. 1989). While the precise dynamics of testicular testosterone secretion at the onset of puberty has not been described in either man or monkey, it is reasonable to presume that, since LH secretion is pulsatile at this stage of development (Wu et al. 1993, Manasco et al. 1995, Albertsson-Wikland et al. 1997, Suter et al. 1998, Mitamura et al. 1999, Veldhuis et al. 2001, Crofton et al. 2004), the release of testicular testosterone would also be episodic.
We were therefore surprised to observe continuous release of testosterone, in response to initial intermittent stimulation of the juvenile rhesus monkey testes with exogenous LH, in two studies requiring premature activation of testicular function. This serendipitous finding is presented here.
|
Materials and Methods |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
Fourteen juvenile male rhesus monkeys (Macaca mulatta, 14–19 months old, 2.0–3.2 kg body weight) were used. Eight of these animals comprised a previously published study aimed at establishing the relative role of LH and follicle-stimulating hormone (FSH) in Sertoli cell proliferation at the time of puberty (Ramaswamy et al. 2000b). Four other animals, which served as a control group in an unpublished study, had been implanted with empty s.c. Silastic capsules at least 6 weeks before initiation of LH stimulation. Two additional animals were used to define specifically the initial development of the testicular testosterone response to LH stimulation. Here, it should be noted that, in the rhesus monkey, the pubertal initiation of nocturnal testosterone secretion occurs at approximately 30–36 months of age (Plant 1985).
Access to venous circulation
Each animal was surgically implanted with two indwelling catheters, which provided continuous access to the venous circulation, using a sterile technique under sodium pentobarbital anesthesia (25 mg/kg body weight, i.v. Nembutal Sodium Solution, Abbott Laboratories, Chicago, IL, USA) or isoflurane inhalation (1–2.5% with oxygen), as described previously (Ramaswamy et al. 2003, Shahab et al. 2003). The post-surgical care of the first group of eight animals has been described previously (Ramaswamy et al. 1999, 2000b), and this was also employed for the two animals used to study the early testicular response to LH stimulation. The remaining four animals each received a single i.m. injection of penicillin (Pen-G, 40 000 U/kg body weight, Phoenix Pharma Inc., MO, USA) on the day of surgery, and twice-daily i.v. injections of a broad-spectrum antibiotic cefazolin sodium (25 mg/kg body weight, Kefzol, Apothecon, Princeton, NJ, USA or Ancef, GlaxoSmithKline) and an analgesic (Ketofen, 2 mg/kg body weight, Fort Dodge Animal Health, IA, USA) for 4 days. The routine care of animals fitted with a jacket and tether system, and housed in specialized remote-sampling cages has been described previously (Ramaswamy et al. 1999, 2003). The animals were maintained under a controlled photoperiod (lights on 0700 to 1900 h) in accordance with the NIH Guidelines for the Care and Use of Laboratory Animals; the experimental procedures were approved by the Institutional Animal Care and Use Committee.
Hormone infusates
Stock solutions of recombinant single-chain human (sch)LH (300 IU/ml), recombinant human (rh)FSH (200 IU/ml) and recombinant monkey (rm)FSH (National Hormone and Peptide Program (NHPP, rec moFSH-I-1, AFP6940A) and rmLH (NHPP, rec moLH-I-1, Bio, AFP6936A), both at 1 µg/10 µl, were prepared in Dulbecco’s PBS (DPBS without CaCl2 and MgSO4, Gibco).
Experimental design
Stimulation with schLH The details of this experiment, including the preparation of custom gonadotropin infusates for each animal, have been reported previously (Ramaswamy et al. 2000b). In brief, groups of four juvenile monkeys each received, beginning on day 0, intermittent i.v. infusions of schLH, either alone or in combination with rhFSH (3 and 2 IU/kg per pulse respectively), as a 1-min bolus pulse (2 ml) every 3 h for 11 days. A single blood sample was taken prior to initiation of the hormone infusion on day 0. The profiles of circulating gonadotropin concentrations resulting from the intermittent infusion of the recombinant hormones, and the testicular testosterone responses to exogenous stimulation with LH, were determined in a series of frequent blood samples. Samples were collected, during a 3-h inter-pulse interval, at ~5–10 min before and at 3, 20, 40, 60 and 170 min after a pulse infusion of schLH on days 1 and 8 of the experiment. In two of the four animals receiving schLH alone, additional blood samples were collected at 80 and 120 min after the pulse infusion.
Two additional animals received an intermittent infusion of schLH alone, at the dose described above. In this experiment, blood samples were collected at ~5–10 min before and at 3, 20, 40, 80 and 170 min after a pulse infusion of vehicle (DPBS), and after the first, second and fourth pulse during the initiation of the schLH intermittent infusion.
Stimulation with rmLH A custom infusate of rmLH (in combination with rmFSH) was prepared for each animal in sterile DPBS containing 2 mg/ml cefazolin sodium (Kefzol or Ancef) and 1% serum from the respective monkey. The doses of rmLH and rmFSH used were 600 and 30 ng/kg per pulse respectively. These doses for rmLH and rmFSH were selected since they produced circulating levels of the respective hormone in the range seen in the adult monkey (Ramaswamy et al. 1998, El Majdoubi et al. 2000).
For this experiment, the animals each received, beginning on day 0, intermittent i.v. infusions of rmLH (in combination with rmFSH) as a 1-min bolus pulse (1 ml) every 3 h. Circulating concentrations of infused rmLH, and the testicular testosterone response were determined in a series of frequent blood samples. Samples were collected, during a 3-h inter-pulse interval, at ~5–10 min before and at 5, 20, 40, 60, 80, 100 and 170 min after infusion of a gonadotropin pulse on days 1, 2, 4 and 8–10 of the experiment. In order to obtain baseline hormone concentrations, an identical series of blood samples was collected during a ‘mock’ 3-h window a few days prior to the initiation of gonadotropin treatment.
Assays
Gonadotropins Circulating concentrations of infused schLH were determined using an assay kit specific for hLH (Technicon Immuno-1 System, Bayer) as described previously (Ramaswamy et al. 2000b). Circulating concentrations of infused rmFSH and rmLH were determined using homologous (cynomolgus) RIAs as described previously (Ramaswamy et al. 1998, El Majdoubi et al. 2000). The mean sensitivity of the LH assay was 0.12 ng/ml and the intra- and inter-assay coefficients of variation were less than 5% and 4.4% respectively.
Testosterone Circulating concentrations of testosterone were determined using either a previously described RIA employing antiserum T3–125 (Plant 1981) or a commercially available solid-phase RIA kit (Coat-A-Count, Total T (TKTT), Diagnostic Products Corporation, LA, USA). The mean sensitivity of the two assays was approximately 0.065 and 0.028 ng/ml respectively. The intra- and inter-assay coefficients of variation for the former assay were 7.7% and 12.9% respectively; those representative of the latter assay were 4.5% and 7.9% respectively.
Statistical analyses
The significance of differences between mean hormone concentrations was determined by Student’s t-test, or by one-way or multifactor ANOVA with repeated measures followed by the Student–Newman–Keuls multiple-range test, as appropriate. Hormone levels below the sensitivity of the assay were assigned a value equivalent to the minimum detectable concentration in the respective assay. All data are expressed as means ± S.E.M. and statistical significance was accepted at P
0.05.
|
Results |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
Before stimulation with schLH, circulating concentrations of immunoactive hLH were undetectable (Ramaswamy et al. 2000b). Initiation of the intermittent schLH infusions produced an episodic pattern in the circulating concentration of immunoactive hLH with peak values on days 1 and 8 ranging from 3.60 to 6.20 IU/l and from 2.20 to 4.30 IU/l respectively (Fig. 1
). The mean concentrations of immunoactive hLH in the circulation during a 3-h window of frequent blood sampling on days 1 and 8 of LH stimulation, alone, were 1.86 ± 0.16 and 1.24 ± 0.18 IU/l respectively (Table 1). The corresponding plasma LH concentrations in the group treated in combination with rhFSH were similar (Fig. 1 and Table 1). In both groups, LH concentrations on days 1 and 8 were significantly different.
|
|
). At this time, there was no evidence of an episodic pattern of testosterone secretion (Fig. 1). By day 8 of schLH stimulation, however, the pattern of testosterone secretion had switched to a distinct episodic mode, as reflected by the time course of circulating testosterone (Fig. 1). The mean plasma testosterone concentrations during the initial apulsatile phase of secretion (day 1) and the subsequent pulsatile mode of release (day 8) of this steroid were 4.04 ± 0.54 and 2.96 ± 0.63 ng/ml respectively (Table 1). The more comprehensive sampling paradigm employed in two of the four animals receiving schLH, alone, substantiated the apulsatile mode of testosterone release during the initial day of LH stimulation (data not shown).
In the two additional animals, in which the initial testicular testosterone response to LH stimulation was monitored, the circulating profiles of immunoactive hLH were similar to those seen in the first experiment (Fig. 2). As in the first group of animals, a robust testosterone response was also observed after 24 h of LH stimulation. Circulating testosterone levels during the first, second and fourth schLH pulse, however, remained within the range observed during vehicle infusion (Fig. 2).
|
and Table 1). During combined gonadotropin treatment, the mean testosterone concentrations in the circulation on days 1 and 8 were 2.32 ± 0.27 and 2.24 ± 0.33 ng/ml respectively (Table 1). Stimulation with rmLH
Prior to treatment with homologous gonadotropins, circulating concentrations of endogenous LH were undetectable (Table 1). Following the initiation of the intermittent infusion of rmLH (in combination with rmFSH), the expected episodic pattern of circulating LH concentrations was noted (Fig. 3). Mean LH concentration on days 1, 2, 4 and 8–10 were similar (Table 1).
|
). Similar to the situation noted with the schLH infusion, there was no evidence for episodic testosterone release at this time (Fig. 3). An episodic discharge of this steroid, however, was noted as early as day 2 of intermittent rmLH treatment (Fig. 3) and, by day 4, the pattern of testosterone secretion was unequivocally episodic; a mode of release that was sustained for the 8–10 days of treatment (Fig. 3). The switch from a continuous to pulsatile mode of testosterone release was associated with a progressive decrease in mean testosterone concentrations, with values of 6.01 ± 1.37, 3.21 ± 0.46 and 2.35 ± 0.20 ng/ml noted on days 2, 4 and 8–10 respectively. The mean testosterone concentration on day 2 was significantly different from those on subsequent days (Table 1). |
Discussion |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
The mechanisms responsible for the initial continuous pattern of testosterone release remain to be determined. Several possibilities may be considered. First, during the 24 h of the intermittent LH infusion, the progenitor Leydig cells in the interstitium of the juvenile testis may not receive a pulsatile LH signal from the vascular compartment. This view is supported from observations in rats that LH or hCG stimulation results in changes in interstitial blood flow and capillary permeability (Setchell & Sharpe 1981, Turner & Rhoades 1995, Setchell et al. 2002). Secondly, it has been suggested that the endothelial cells of the testis may play a role in mediating LH-stimulated testosterone secretion (Ghinea & Milgrom 1995, Setchell et al. 2002), and if this is the case, this relationship may change with time. Thirdly, the release of testosterone from the progenitor Leydig cells may initially be intrinsically continuous. In this regard, it is well established that, at the time of puberty, expansion of this population of cells is associated with maturation of cellular, biochemical and molecular machinery necessary for the synthesis and secretion of testosterone (Chemes et al. 1985, Saez 1994, Benton et al. 1995, Rey et al. 1995, Ge & Hardy 1998, Lejuene et al. 1998, Mendis-Handagama 2000, Mendis-Handagama & Ariyaratne 2001, Prince 2001, O’Shaughnessy et al. 2002, Haider 2004). Fourthly, during the first 24 h of LH stimulation, secretory activity by progenitor Leydig cells may not be synchronized. This view is based on the observations that during pubertal testicular development recruitment of progenitor Leydig cells occurs following exposure to gonadotropins (Mancini et al. 1963, Fouquet et al. 1984, Prince 1984, 2001, Nistal et al. 1986, Saez 1994). Such a developmental event involving differentiation of more than one cell type (i.e. fibroblasts, and mesenchymal and immature Leydig cells) may result in subpopulations of steroidogenic cells that respond to LH stimulation with variable latencies. Lastly, but unlikely in our view, a pulsatile mode of testosterone release from interstitial cells may not be initially transmitted to the vascular compartment.
Whatever the explanation, a pulsatile profile in the release of testosterone had emerged by day 2 of LH stimulation, although a component of the release pattern remained continuous, as reflected by elevated basal testosterone levels. The pulsatile mode of testosterone secretion continued to mature while the continuous pattern of testosterone release regressed and, by day 8, the profile of circulating testosterone was similar to that observed in normal adult monkeys (Plant 1981). It is to be noted, however, that the switch from a continuous to a fully adult pulsatile mode of testosterone release was generally associated with a reduction in testicular testosterone secretion as reflected by a decline in mean levels of this steroid in the circulation.
At the cellular level, the mechanisms involved in the maturation of progenitor Leydig cells in to adult Leydig cells may include, in addition to those resulting directly from activation of LH signaling, autocrine actions of testosterone on the Leydig cell and/or paracrine actions of Sertoli cell factors induced secondarily in response to androgen receptor activation (Hardy et al. 1990, Gnessi et al. 1997, Hales 2002, Haider 2004). Additionally, it is to be recalled that the testes are innervated by both intrinsic and extrinsic systems, which are known to exhibit a marked degree of plasticity during the peripubertal period (Prince 1992, Setchell et al. 1994, Mayerhofer 1996, Frungieri et al. 2000, Suburo et al. 2002, Geigerseder et al. 2004). Thus, it may also be possible that neuronal remodeling resulting from the exogenous LH stimulation of the juvenile testes may contribute to the switch from a continuous to a pulsatile mode of testosterone release.
Whether the initiation of testicular testosterone secretion during spontaneous puberty involves an initial continuous phase of steroid release is unclear. In this regard, it should be noted that during normal pubertal development the progenitor Leydig cells are probably not exposed to an abrupt, invariant and robust LH stimulation, as was produced in the present study. Instead, both LH pulse frequency and amplitude increase gradually (Plant 1994, 2001), which, in turn, would provide a progressively ascending LH stimulus to the progenitor Leydig cells.
Finally, the finding that progenitor Leydig cells exhibit the potential to robustly secrete testosterone in a continuous mode in response to pulsatile LH stimulation raises the theoretical question of why adult Leydig cells respond to the same LH stimulus with an episodic pattern of testosterone secretion. We speculate that this may be related to the notion that episodic testosterone secretion is required for the operation of the HPG axis governing the testes. Specifically, while functions of the seminiferous tubules and the accessory sex structures are maintained in the face of continuous exposure to testosterone, we suggest that the activity of the hypothalamic–pituitary component of this axis may be down-regulated by physiological levels of testosterone presented in a continuous fashion.
|
Acknowledgements |
|---|
|
Funding |
|---|
This work was supported by NIH grants HD08610 and HD13254 (T M P), HD32473 (G R M), and ES011755–01 and the Competitive Medical Research Fund (CMRF) of the University of Pittsburgh Medical Center (S R). The authors declare no conflict of interest that would prejudice the impartiality of the research.
|
References |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
Ascoli MM, Fanelli F & Segaloff DL 2002 The lutropin/choriogonadotropin receptor, a 2002 perspective. Endocrine Reviews 23 141–174.
Benton L, Shan L-X & Hardy MP 1995 Differentiation of adult Leydig cells. Journal of Steroid Biochemistry and Molecular Biology 53 61–68.[CrossRef][ISI][Medline]
Chase DJ, Schanbacher BD & Lunstra DD 1988 Effects of pulsatile and continuous luteinizing hormone (LH) infusions on testosterone response to LH in rams actively immunized against gonadotropin-releasing hormone. Endocrinology 123 816–826.[Abstract]
Chemes HE, Gottlieb SE, Pasqualini T, Domenichini E, Rivarola MA & Bergada C 1985 Response to acute hCG stimulation and steroidogenic potential of Leydig cell fibroblast precursors in humans. Journal of Andrology 6 102–112.
Crofton PM, Evans AEM, Wallace AM, Groome NP & Kelnar CJH 2004 Nocturnal secretory dynamics of inhibin B and testosterone in pre- and peripubertal boys. Journal of Clinical Endocrinology and Metabolism 89 867–874.
El Majdoubi M, Ramaswamy S, Sahu A & Plant TM 2000 Effects of orchidectomy on levels of the mRNAs encoding gonadotropin-releasing hormone and other hypothalamic peptides in the adult male rhesus monkey (Macaca mulatta). Journal of Neuroendocrinology 12 167–176.[CrossRef][ISI][Medline]
Ewing LL & Keeney DS 1993 Leydig cells: structure and function. In Cell and Molecular Biology of the Testis, pp 137–165. Eds C Desjardins & LL Ewing. New York: Oxford University Press.
Fouquet JP, Meusy-Dessolle N & Dang DC 1984 Relationship between Leydig cell morphometry and plasma testosterone during postnatal development of the monkey, Macaca fascicularis. Reproduction, Nutrition and Development 24 281–296.
Frungieri MB, Urbanski HF, Hohne-Zell B & Mayerhofer A 2000 Neuronal elements in the testis of the rhesus monkey: ontogeny, characterization and relationship to testicular cells. Neuroendocrinology 71 43–50.[CrossRef][ISI][Medline]
Ge R-S & Hardy MP 1998 Variation in the end products of androgen biosynthesis and metabolism during postnatal differentiation of rat Leydig cells. Endocrinology 139 3787–3795.
Geigerseder C, Doepner RF, Thalhammer A, Krieger A & Mayerhofer A 2004 Stimulation of TM3 Leydig cell proliferation via GABAA receptors: A new role for testicular GABA. Reproductive Biology and Endocrinology 2 13.
Ghinea N & Milgrom E 1995 Transport of protein hormones through the vascular endothelium. Journal of Endocrinology 145 1–9.
Gnessi L, Fabri A & Spera G 1997 Gonadal peptides as mediators of development and functional control of the testis: An integrated system with hormones and local environment. Endocrine Reviews 18 541–609.
Haider SG 2004 Cell biology of Leydig cells in the testis. International Review of Cytology 233 181–241.[ISI][Medline]
Hales DB 2002 Testicular macrophage modulation of Leydig cell steroidogenesis. Journal of Reproductive Immunology 57 3–18.[CrossRef][ISI][Medline]
Hardy MP, Kelce WR, Klinefelter GR & Ewing LL 1990 Differentiation of Leydig cell precursors in vitro: A role for androgen. Endocrinology 127 488–490.[Abstract]
Huhtaniemi I 1996 Ontogeny of luteinizing hormone action in the male. In The Leydig Cell, pp 365–382. Eds AH Payne, MP Hardy & LD Russell. Vienna: Cache River Press.
Lejeune H, Habert R & Saez JM 1998 Origin, proliferation and differentiation of Leydig cells. Journal of Molecular Endocrinology 20 1–25.[CrossRef][ISI][Medline]
Manasco PK, Umbach DM, Muly SM, Godwin DC, Negro-Vilar A, Culler MD & Underwood LE 1995 Ontogeny of gonadotropin, testosterone, and inhibin secretion in normal boys through puberty based on overnight serial sampling. Journal of Clinical Endocrinology and Metabolism 80 2046–2052.[Abstract]
Mancini RE, Vilar O, Lavieri JC, Andrada JA & Heinrich JJ 1963 Development of Leydig cells in the normal human testis: a cytological, cytochemical and quantitative study. American Journal of Anatomy 112 203–214.[CrossRef]
Mayerhofer A 1996 Leydig cell regulation by catecholamines and neuroendocrine messengers. In The Leydig Cell, pp 408–418. Eds AH Payne, MP Hardy & LD Russell. Vienna: Cache River Press.
Mendis-Handagama SM 2000 Peroxisomes and intracellular cholesterol traffcking in adult rat Leydig cells following luteinizing hormone stimulation. Tissue and Cell 32 102–106.[CrossRef][ISI][Medline]
Mendis-Handagama SM & Ariyaratne HBS 2001 Differentiation of the adult Leydig cell population in the postnatal testis. Biology of Reproduction 65 660–671.
Mitamura R, Yano K, Suzuki N, Ito Y, Makita Y & Okuno A 1999 Diurnal rhythms of luteinizing hormone, follicle-stimulating hormone, and testosterone secretion before the onset of male puberty. Journal of Clinical Endocrinology and Metabolism 84 29–37.
Nistal M, Paniagua R, Regadera J, Santamaria L & Amat P 1986 A quantitative morphological study of human Leydig cells from birth to adulthood. Cell and Tissue Research 246 229–236.[CrossRef][ISI][Medline]
O’Shaughnessy PJ, Willerton L & Baker PJ 2002 Changes in Leydig cell gene expression during development in the mouse. Biology of Reproduction 66 966–975.
Plant TM 1981 Time courses of concentrations of circulating gonadotropin, prolactin, testosterone, and cortisol in adult male rhesus monkeys (Macaca mulatta) throughout the 24 h light-dark cycle. Biology of Reproduction 25 244–252.[Abstract]
Plant TM 1985 A study of the role of the postnatal testis in determining the ontogeny of gonadotropin secretion in the male rhesus monkey (Macaca mulatta). Endocrinology 116 1341–1350.[Abstract]
Plant TM 1994 Puberty in primates. In The Physiology of Reproduction, edn 2, pp 453–485. Eds E Knobil & JD Neil. New York: Raven Press Ltd.
Plant TM 2001 Neurobiological bases underlying the control of the onset of puberty in the rhesus monkey: A representative higher primate. Frontiers in Neuroendocrinology 22 107–139.[CrossRef][ISI][Medline]
Plant TM, Gay VL, Marshall GR & Arslan M 1989 Puberty in monkeys is triggered by chemical stimulation of the hypothalamus. PNAS 86 2506–2510.
Prince FP 1984 Ultrastructure of immature Leydig cells in the human prepubertal testis. Anatomical Record 209 165–176.[CrossRef][Medline]
Prince FP 1992 Ultrastructural evidence of indirect and direct autonomic innervation of human Leydig cells: comparison of neonatal, childhood and pubertal ages. Cell and Tissue Research 269 383–390.[CrossRef][ISI][Medline]
Prince FP 2001 The triphasic nature of Leydig cell development in humans, and comments on nomenclature. Journal of Endocrinology 168 213–216.[Abstract]
Ramaswamy S, Pohl CR, McNeilly AS, Winters SJ & Plant TM 1998 The time course of follicle-stimulating hormone suppression by recombinant human inhibin A in the adult male rhesus monkey (Macaca mulatta). Endocrinology 139 3409–3415.
Ramaswamy S, Marshall GR, McNeilly AS & Plant TM 1999 Evidence that in a physiological setting Sertoli cell number is the major determinant of circulating concentrations of inhibin B in the adult male rhesus monkey (Macaca mulatta). Journal of Andrology 20 430–434.
Ramaswamy S, Marshall GR, McNeilly AS & Plant TM 2000a Dynamics of the follicle-stimulating hormone (FSH)-inhibin B feedback loop and its role in regulating spermatogenesis in the adult male rhesus monkey (Macaca mulatta) as revealed by unilateral orchidectomy. Endocrinology 141 18–27.
Ramaswamy S, Plant TM & Marshall GR 2000b Pulsatile stimulation with recombinant single chain human luteinizing hormone elicits precocious Sertoli cell proliferation in the juvenile male rhesus monkey (Macaca mulatta). Biology of Reproduction 63 82–88.
Ramaswamy S, Marshall GR, Pohl CR, Friedman RL & Plant TM 2003 Inhibitory and stimulatory regulation of testicular inhibin B secretion by luteinizing hormone and follicle-stimulating hormone, respectively, in the rhesus monkey (Macaca mulatta). Endocrinology 144 1175–1185.
Rey R, Campo S, Ayuso S, Nagle C & Chemes H 1995 Testicular steroidogenesis in the Cebus monkey throughout postnatal development. Biology of Reproduction 52 997–1002.[Abstract]
Saez JM 1994 Leydig cells: endocrine, paracrine, and autocrine regulation. Endocrine Reviews 15 574–626.[CrossRef][ISI][Medline]
Setchell BP & Sharpe RM 1981 Effect of injected human chorionic gonadotropin on capillary permeability, extracellular fluid volume and the flow of lymph and blood in the testes of rats. Journal of Endocrinology 91 245–254.
Setchell BP, Maddocks S, Brooks DE 1994 Anatomy, vasculature, innervation, and fluids of the male reproductive tract. In The Physiology of Reproduction, edn 2, pp 1063–1175. Eds E Knobil & JD Neil. New York: Raven Press Ltd
Setchell BP, Pakarinen P & Huhtaniemi I 2002 How much LH do the Leydig cells see? Journal of Endocrinology 175 375–382.[Abstract]
Shahab M, Balasubramaniam A, Sahu A & Plant TM 2003 Central nervous system receptors involved in mediating the inhibitory action of neuropeptide Y on luteinizing hormone secretion in the male rhesus monkey (Macaca mulatta). Journal of Neuroendocrinology 15 965–970.[CrossRef][ISI][Medline]
Suburo AM, Chiocchio SR, Soler MVC, Nieponice A & Tramezzani JH 2002 Peptidergic innervation of blood vessels and interstitial cells in the testis of the cat. Journal of Andrology 23 121–134.[Abstract]
Suter KJ, Pohl CR & Plant TM 1998 The pattern and tempo of the pubertal reaugmentation of open-loop pulsatile gonadotropin-releasing hormone release assessed indirectly in the male rhesus monkey (Macaca mulatta). Endocrinology 139 2774–2783.
Turner TT & Rhoades CP 1995 Testicular capillary permeability: The movement of luteinizing hormone from the vascular to the interstitial compartment. Journal of Andrology 16 417–423.
Veldhuis JD, Pincus SM, Mitamura R, Yano K, Suzuki N, Ito Y, Makita Y & Okuno A 2001 Developmentally delimited emergence of more orderly luteinizing hormone and testosterone secretion during late puberty in boys. Journal of Clinical Endocrinology and Metabolism 86 80–89.
Wu FCW, Brown DC, Butler GE, Stirling HF & Kelnar CJH 1993 Early morning plasma testosterone is an accurate predictor of imminent pubertal development in prepubertal boys. Journal of Clinical Endocrinology and Metabolism 76 26–31.[Abstract]
Received 4 May 2004
Accepted 15 June 2004
This article has been cited by other articles:
|
|
 |
|
  S. Ramaswamy Pubertal Augmentation in Juvenile Rhesus Monkey Testosterone Production Induced by Invariant Gonadotropin Stimulation Is Inhibited by Estrogen J. Clin. Endocrinol. Metab., October 1, 2005; 90(10): 5866 - 5875. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | CONTACT US | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
) and testosterone (•) during selected 3-h inter-gonadotropin pulse intervals following the initiation, on day 0, of an intermittent i.v. infusion of schLH, either alone (top panels) or in combination with rhFSH (bottom panels). Note the switch from an initial continuous mode of testosterone release on day 1(D1) to that of pulsatile mode of release of this steroid on day 8(D8); the latter is reminiscent of the pattern of testosterone release in the adult monkey (
