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Abstract
A healthy nutritional state is required for all aspects of reproduction and is signaled by the adipokine leptin. Leptin acts in a relatively narrow concentration range: too much or too little will compromise fertility. The leptin signal timing is important to prepubertal development in both sexes. In the brain, leptin acts on ventral premammillary neurons which signal kisspeptin (Kiss1) neurons to stimulate gonadotropin releasing hormone (GnRH) neurons. Suppression of Kiss1 neurons occurs when agouti-related peptide neurons are activated by reduced leptin, because leptin normally suppresses these orexigenic neurons. In the pituitary, leptin stimulates production of GnRH receptors (GnRHRs) and follicle-stimulating hormone at midcycle, by activating pathways that derepress actions of the messenger ribonucleic acid translational regulatory protein Musashi. In females, rising estrogen stimulates a rise in serum leptin, which peaks at midcycle, synchronizing with nocturnal luteinizing hormone pulses. The normal range of serum leptin levels (10-20 ng/mL) along with gonadotropins and growth factors promote ovarian granulosa and theca cell functions and oocyte maturation. In males, the prepubertal rise in leptin promotes testicular development. However, a decline in leptin levels in prepubertal boys reflects inhibition of leptin secretion by rising androgens. In adult males, leptin levels are 10% to 50% of those in females, and high leptin inhibits testicular function. The obesity epidemic has elucidated leptin resistance pathways, with too much leptin in either sex leading to infertility. Under conditions of balanced nutrition, however, the secretion of leptin is timed and regulated within a narrow level range that optimizes its trophic effects.
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Affiliation(s)
- Gwen V Childs
- Department of Neurobiology and Developmental Sciences, University of Arkansas for Medical Sciences, Little Rock, Arkansas
- Correspondence: Gwen V. Childs, PhD, University of Arkansas for Medical Sciences, Little Rock, AR, USA. E-mail:
| | - Angela K Odle
- Department of Neurobiology and Developmental Sciences, University of Arkansas for Medical Sciences, Little Rock, Arkansas
| | - Melanie C MacNicol
- Department of Neurobiology and Developmental Sciences, University of Arkansas for Medical Sciences, Little Rock, Arkansas
| | - Angus M MacNicol
- Department of Neurobiology and Developmental Sciences, University of Arkansas for Medical Sciences, Little Rock, Arkansas
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Silva JF, Henriques PC, Campideli-Santana AC, Araujo-Lopes R, Aquino NSS, Hipolito LTM, Lopes-Aguiar C, Reis AM, Grattan DR, Szawka RE. Estradiol Potentiates But Is Not Essential for Prolactin-Induced Suppression of Luteinizing Hormone Pulses in Female Rats. Endocrinology 2020; 161:5735034. [PMID: 32052048 DOI: 10.1210/endocr/bqaa022] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/19/2019] [Accepted: 02/10/2020] [Indexed: 12/17/2022]
Abstract
Hyperprolactinemia causes infertility by suppressing gonadotropin-releasing hormone (GnRH) and luteinizing hormone (LH) secretion. Because effects of prolactin (PRL) on the hypothalamus usually require estradiol (E2), we investigated the role of E2 in PRL-induced suppression of LH pulses. Ovariectomized (OVX) rats treated with oil or E2 (OVX + E2) received a subcutaneous injection of ovine PRL (oPRL) 30 minutes before serial measurement of LH in the tail blood by enzyme-linked immunosorbent assay. E2 reduced pulsatile LH secretion. oPRL at 1.5 mg/kg further reduced LH pulse frequency in OVX + E2 but had no effect in OVX rats. The higher dose of 6-mg/kg oPRL decreased LH pulse frequency in both OVX and OVX + E2 rats, whereas pulse amplitude and mean LH levels were lowered only in OVX + E2 rats. Kisspeptin immunoreactivity and Kiss1 messenger ribonucleic acid (mRNA) levels were decreased in the arcuate nucleus (ARC) of OVX + E2 rats. oPRL decreased both kisspeptin peptide and gene expression in the ARC of OVX rats but did not alter the already low levels in OVX + E2 rats. In the anteroventral periventricular nucleus, oPRL did not change kisspeptin immunoreactivity and, paradoxically, increased Kiss1 mRNA only in OVX + E2 rats. Moreover, oPRL effectively reduced Gnrh expression regardless of E2 treatment. In this study we used tail-tip blood sampling to determine the acute effect of PRL on LH pulsatility in female rats. Our findings characterize the role of E2 in the PRL modulation of hypothalamic components of the gonadal axis and LH release, demonstrating that E2 potentiates but is not essential for the suppression of pulsatile LH secretion caused by hyperprolactinemia.
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Affiliation(s)
- Juneo F Silva
- Departamento de Fisiologia e Biofísica, Instituto de Ciencias Biologicas, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil
- Centro de Microscopia Eletronica, Departamento de Ciencias Biologicas, Universidade Estadual de Santa Cruz, Campus Soane Nazare de Andrade, Ilheus, Brazil
| | - Patricia C Henriques
- Departamento de Fisiologia e Biofísica, Instituto de Ciencias Biologicas, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil
| | - Ana C Campideli-Santana
- Departamento de Fisiologia e Biofísica, Instituto de Ciencias Biologicas, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil
| | - Roberta Araujo-Lopes
- Departamento de Fisiologia e Biofísica, Instituto de Ciencias Biologicas, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil
| | - Nayara S S Aquino
- Departamento de Fisiologia e Biofísica, Instituto de Ciencias Biologicas, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil
| | - Laisa T M Hipolito
- Departamento de Fisiologia e Biofísica, Instituto de Ciencias Biologicas, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil
| | - Cleiton Lopes-Aguiar
- Departamento de Fisiologia e Biofísica, Instituto de Ciencias Biologicas, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil
| | - Adelina M Reis
- Departamento de Fisiologia e Biofísica, Instituto de Ciencias Biologicas, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil
| | - David R Grattan
- Centre for Neuroendocrinology and Department of Anatomy, Otago School of Medical Sciences, University of Otago, Dunedin, New Zealand
| | - Raphael E Szawka
- Departamento de Fisiologia e Biofísica, Instituto de Ciencias Biologicas, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil
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3
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Chojnowska K, Czerwinska J, Kaminski T, Kaminska B, Kurzynska A, Bogacka I. Leptin plasma concentrations, leptin gene expression, and protein localization in the hypothalamic-pituitary-gonadal and hypothalamic-pituitary-adrenal axes of the European beaver ( Castor fiber ). Theriogenology 2017; 87:266-275. [DOI: 10.1016/j.theriogenology.2016.09.001] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2016] [Revised: 08/31/2016] [Accepted: 09/01/2016] [Indexed: 12/22/2022]
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Donato J, Frazão R, Fukuda M, Vianna CR, Elias CF. Leptin induces phosphorylation of neuronal nitric oxide synthase in defined hypothalamic neurons. Endocrinology 2010; 151:5415-27. [PMID: 20881244 PMCID: PMC2954713 DOI: 10.1210/en.2010-0651] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Studies have indicated that the neurotransmitter nitric oxide (NO) mediates leptin's effects in the neuroendocrine reproductive axis. However, the neurons involved in these effects and their regulation by leptin is still unknown. We aimed to determine whether NO neurons are direct targets of leptin and by which mechanisms leptin may influence neuronal NO synthase (nNOS) activity. Nicotinamide adenine dinucleotide phosphate diaphorase activity and leptin-induced phosphorylation of signal transducer and activator of transcription-3 immunoreactivity were coexpressed in subsets of neurons of the medial preoptic area, the paraventricular nucleus of the thalamus, the arcuate nucleus (Arc), the dorsomedial nucleus of the hypothalamus (DMH), the posterior hypothalamic area, the ventral premammillary nucleus (PMV), the parabrachial nucleus, and the dorsal motor nucleus of the vagus nerve. Fasting blunted nNOS mRNA expression in the medial preoptic area, Arc, DMH, PMV, and posterior hypothalamic area, and this effect was not restored by acute leptin administration. No difference in the number of neurons expressing nNOS immunoreactivity was noticed comparing hypothalamic sections of fed (wild type and ob/ob), fasted, and fasted leptin-treated mice. However, we found that in states of low leptin levels, as in fasting, or lack of leptin, as in ob/ob mice, the number of neurons expressing the phosphorylated form of nNOS is decreased in the Arc, DMH, and PMV. Notably, acute leptin administration to fasted wild-type mice restored the number of phosphorylated form of nNOS neurons to that observed in fed wild-type mice. Herein we identified the first-order neurons potentially involved in NO-mediated effects of leptin and demonstrate that leptin regulates nNOS activity predominantly through posttranslational mechanisms.
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Affiliation(s)
- Jose Donato
- Department of Internal Medicine, Division of Hypothalamic Research, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA
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Wu Y, Luo H, Liu J, Kang D, McNeilly AS, Cui S. LIM homeodomain transcription factor Isl-1 enhances follicle stimulating hormone-beta and luteinizing hormone-beta gene expression and mediates the activation of leptin on gonadotropin synthesis. Endocrinology 2010; 151:4787-800. [PMID: 20702576 DOI: 10.1210/en.2010-0208] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The Lin-11, Isl-1, and Mec-3 (LIM) homeodomain transcription factor Isl-1 has been reported to be involved in pituitary development in the early stages of mouse embryogenesis. Our recent studies have shown that Isl-1 is mainly located in the pituitary gonadotropes throughout pituitary development and persists to adulthood. We still do not know the physiological functions of Isl-1 expression and its related mechanisms in the pituitary gland. The aim of the present study was to examine the hypothesis that Isl-1 is involved in regulating pituitary gonadotropin hormone (FSH/LH) production by activating FSHβ and LHβ gene expressions. We have shown that Isl-1 activates FSHβ and LHβ subunit promoters and endogenous gene transcription in LβT2 cells. In addition, Isl-1 overexpression significantly increased FSH synthesis and secretion but not LH. The actions of Isl-1 were not observed when the homeodomain or LIM1 domains are mutated. This demonstrates that Isl-1 induction of FSHβ and LHβ is by both direct and indirect binding of Isl-1 to DNA sequences. Furthermore, Isl-1 expressional level was up-regulated in LβT2 cells after exposure to GnRH, activin, and leptin. However, RNA interference-induced knockdown of Isl-1 significantly reduced the effect of leptin but did not obviously influence the stimulating effects of GnRH and activin on LH and FSH production. In conclusion, the results demonstrate that the LIM-homeodomain transcription factor Isl-1 functions to increase FSHβ/LHβ gene transcription, and mediates the effects of leptin on gonadotropin synthesis.
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Affiliation(s)
- Yingjie Wu
- State Key Laboratory of Agrobiotechnology, College of Biological Sciences, China Agricultural University, Beijing 100193, People's Republic of China
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De Paul AL, Attademo AM, Carón RW, Soaje M, Torres AI, Jahn GA, Celis ME. Neuropeptide glutamic-isoleucine (NEI) specifically stimulates the secretory activity of gonadotrophs in primary cultures of female rat pituitary cells. Peptides 2009; 30:2081-7. [PMID: 19729046 DOI: 10.1016/j.peptides.2009.08.022] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/23/2008] [Revised: 08/14/2009] [Accepted: 08/25/2009] [Indexed: 11/17/2022]
Abstract
The neuropeptide EI (NEI) is derived from proMCH. It activates GnRH neurons, and has been shown to stimulate the LH release following intracerebroventricular administration in several experimental models. The aim of the present paper was to evaluate NEI actions on pituitary hormone secretion and cell morphology in vitro. Pituitary cells from female rats were treated with NEI for a wide range of concentrations (1-400x10(-8)M) and time periods (1-5h). The media were collected and LH, FSH, PRL, and GH measured by RIA. The interaction between NEI (1, 10 and 100x10(-8)M) and GnRH (0.1 and 1x10(-9)M) was also tested. Pituitary cells were harvested for electron microscopy, and the immunogold immunocytochemistry of LH was assayed after 2 and 4h of NEI incubation. NEI (100x10(-8)M) induced a significant LH secretion after 2h of stimulus, reaching a maximum response 4h later. A rapid and remarkable LH release was induced by NEI (400x10(-8)M) 1h after stimulus, attaining its highest level at 2h. However, PRL, GH and FSH were not affected. NEI provoked ultrastructural changes in the gonadotrophs, which showed accumulations of LH-immunoreactive granules near the plasma membrane and exocytotic images, while the other populations exhibited no changes. Although NEI (10x10(-8)M), caused no action when used alone, its co-incubation with GnRH (1x10(-9)M), promoted a slight but significant increase in LH. These results demonstrate that NEI acts at the pituitary level through a direct action on gonadotrophs, as well as through interaction with GnRH.
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Affiliation(s)
- Ana Lucía De Paul
- Centro de Microscopía Electrónica, Universidad Nacional de Córdoba, Ciudad Universitaria, Argentina.
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Kim D, Kwon YK, Cho KH. The biphasic behavior of incoherent feed-forward loops in biomolecular regulatory networks. Bioessays 2008; 30:1204-11. [DOI: 10.1002/bies.20839] [Citation(s) in RCA: 80] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
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Mastronardi CA, Walczewska A, Yu WH, Karanth S, Parlow AF, McCann SM. The Possible Role of Prolactin in the Circadian Rhythm of Leptin Secretion in Male Rats. ACTA ACUST UNITED AC 2008. [DOI: 10.1111/j.1525-1373.2000.22414.x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Crane C, Akhter N, Johnson BW, Iruthayanathan M, Syed F, Kudo A, Zhou YH, Childs GV. Fasting and glucose effects on pituitary leptin expression: is leptin a local signal for nutrient status? J Histochem Cytochem 2007; 55:1059-73. [PMID: 17595338 PMCID: PMC2085236 DOI: 10.1369/jhc.7a7214.2007] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Leptin, a potent anorexigenic hormone, is found in the anterior pituitary (AP). The aim of this study was to determine whether and how pituitary leptin-bearing cells are regulated by nutritional status. Male rats showed 64% reductions in pituitary leptin mRNA 24 hr after fasting, accompanied by significant (30-50%) reductions in growth hormone (GH), prolactin, and luteinizing hormone (LH), and 70-80% reductions in target cells for gonadotropin-releasing hormone or growth hormone-releasing hormone. There was a 2-fold increase in corticotropes. Subsets (22%) of pituitary cells coexpressed leptin and GH, and <5% coexpressed leptin and LH, prolactin, thyroid-stimulating hormone, or adrenocorticotropic hormone. Fasting resulted in significant (55-75%) losses in cells with leptin proteins or mRNA, and GH or LH. To determine whether restoration of serum glucose could rescue leptin, LH, and GH, additional fasted rats were given 10% glucose water for 24 hr. Restoring serum glucose in fasted rats resulted in pituitary cell populations with normal levels of leptin and GH and LH cells. Similarly, LH and GH cells were restored in vitro after populations from fasted rats were treated for as little as 1 hr in 10-100 pg/ml leptin. These correlative changes in pituitary leptin, LH, and GH, coupled with leptin's rapid restoration of GH and LH in vitro, suggest that pituitary leptin may signal nutritional changes. Collectively, the findings suggest that pituitary leptin expression could be coupled to glucose sensors like glucokinase to facilitate rapid responses by the neuroendocrine system to nutritional cues.
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Affiliation(s)
- Christopher Crane
- Department of Neurobiology and Developmental Sciences, College of Medicine, University of Arkansas for Medical Sciences, 4301 W. Markham St. Slot 510, Little Rock, AR 72205
| | - Noor Akhter
- Department of Neurobiology and Developmental Sciences, College of Medicine, University of Arkansas for Medical Sciences, 4301 W. Markham St. Slot 510, Little Rock, AR 72205
| | - Brandy W. Johnson
- Department of Neurobiology and Developmental Sciences, College of Medicine, University of Arkansas for Medical Sciences, 4301 W. Markham St. Slot 510, Little Rock, AR 72205
| | - Mary Iruthayanathan
- Division of Endocrinology, Department of Internal Medicine, Roy J. and Lucille A. Carver College of Medicine, The University of Iowa; Bldg 40 VA, Iowa City, Iowa 52242
| | - Farhan Syed
- Department of Neurobiology and Developmental Sciences, College of Medicine, University of Arkansas for Medical Sciences, 4301 W. Markham St. Slot 510, Little Rock, AR 72205
| | - Akihiko Kudo
- Department of Anatomy, Kyorin University School of Medicine, Shinkawa, Mitaka, Tokyo, 1818611, Japan
| | - Yi-Hong Zhou
- Department of Neurological Surgery, University of California Irvine, 101 The City Drive, Building 36, Suite 400 Zot 5397, Orange, CA 92868
| | - Gwen V. Childs
- Department of Neurobiology and Developmental Sciences, College of Medicine, University of Arkansas for Medical Sciences, 4301 W. Markham St. Slot 510, Little Rock, AR 72205
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Akhter N, Johnson BW, Crane C, Iruthayanathan M, Zhou YH, Kudo A, Childs GV. Anterior pituitary leptin expression changes in different reproductive states: in vitro stimulation by gonadotropin-releasing hormone. J Histochem Cytochem 2007; 55:151-66. [PMID: 17046838 PMCID: PMC1780073 DOI: 10.1369/jhc.6a7072.2006] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
This study was designed to learn more about the changes in expression of rat anterior pituitary (AP) leptin during the estrous cycle. QRT-PCR assays of cycling rat AP leptin mRNA showed 2-fold increases from metestrus to diestrus followed by an 86% decrease on the morning of proestrus. Percentages of leptin cells increased in proestrus and pregnancy to 55-60% of AP cells. Dual labeling for leptin proteins and growth hormone (GH) or gonadotropins showed that the rise in leptin protein-bearing cells from diestrus to proestrus was mainly in GH cells. Only 10-20% of leptin cells in male or cycling female rats coexpress gonadotropins. In contrast, 50-73% of leptin cells from pregnant or lactating females coexpress gonadotropins and only 19% coexpress GH, indicating plasticity in the distribution of leptin. Leptin cells expressed GnRH receptors, and estrogen and GnRH together increased the coexpression of leptin mRNA and gonadotropins. GnRH increased cellular leptin proteins three to four times and mRNA 9.8 times in proestrous rats and stimulated leptin secretion in cultures from diestrous, proestrous, and pregnant rats. These regulatory influences, and the high expression of AP leptin during proestrus and pregnancy, suggest a supportive role for leptin during key events involved with reproduction.
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Affiliation(s)
- Noor Akhter
- Department of Neurobiology and Developmental Sciences, College of Medicine, University of Arkansas for Medical Sciences, 4301 W. Markham St., Slot 510, Little Rock, AR 72205, USA.
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Licinio J, Caglayan S, Ozata M, Yildiz BO, de Miranda PB, O'Kirwan F, Whitby R, Liang L, Cohen P, Bhasin S, Krauss RM, Veldhuis JD, Wagner AJ, DePaoli AM, McCann SM, Wong ML. Phenotypic effects of leptin replacement on morbid obesity, diabetes mellitus, hypogonadism, and behavior in leptin-deficient adults. Proc Natl Acad Sci U S A 2004; 101:4531-6. [PMID: 15070752 PMCID: PMC384781 DOI: 10.1073/pnas.0308767101] [Citation(s) in RCA: 365] [Impact Index Per Article: 18.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Genetic mutations in the leptin pathway can be a cause of human obesity. It is still unknown whether leptin can be effective in the treatment of fully established morbid obesity and its endocrine and metabolic consequences in adults. To test the hypothesis that leptin has a key role in metabolic and endocrine regulation in adults, we examined the effects of human leptin replacement in the only three adults identified to date who have genetically based leptin deficiency. We treated these three morbidly obese homozygous leptin-deficient adult patients with recombinant human leptin at low, physiological replacement doses in the range of 0.01-0.04 mg/kg for 18 months. Patients were hypogonadal, and one of them also had type 2 diabetes mellitus. We chose the doses of recombinant methionyl human leptin that would achieve normal leptin concentrations and administered them daily in the evening to model the normal circadian variation in endogenous leptin. The mean body mass index dropped from 51.2 +/- 2.5 (mean +/- SEM) at baseline to 26.9 +/- 2.1 kg/m2 after 18 months of treatment, mainly because of loss of fat mass. We document here that leptin replacement therapy in leptin-deficient adults with established morbid obesity results in profound weight loss, increased physical activity, changes in endocrine function and metabolism, including resolution of type 2 diabetes mellitus and hypogonadism, and beneficial effects on ingestive and noningestive behavior. These results highlight the role of the leptin pathway in adults with key effects on the regulation of body weight, gonadal function, and behavior.
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Affiliation(s)
- Julio Licinio
- Center for Pharmacogenomics, Neuropsychiatric Institute, Department of Psychiatry and Biobehavioral Sciences, David Geffen School of Medicine, University of California, Los Angeles, CA 90095-1761, USA.
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Van Dam EWCM, Roelfsema F, Veldhuis JD, Helmerhorst FM, Frölich M, Meinders AE, Krans HMJ, Pijl H. Increase in daily LH secretion in response to short-term calorie restriction in obese women with PCOS. Am J Physiol Endocrinol Metab 2002; 282:E865-72. [PMID: 11882506 DOI: 10.1152/ajpendo.00458.2001] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We hypothesized that short-term calorie restriction would blunt luteinizing hormone (LH) hypersecretion in obese women with polycystic ovary syndrome (PCOS) and thereby ameliorate the anovulatory endocrine milieu. To test this hypothesis, 15 obese patients with PCOS and nine age- and body mass index-matched healthy women underwent 24-h blood sampling to quantitate plasma LH, leptin, and insulin levels. PCOS subjects were prescribed a very low caloric liquid diet (4.2 MJ/day) for 7 days and were then resampled. Basal and pulsatile LH secretion was threefold higher in PCOS subjects, but plasma insulin and leptin levels were not different in the calorie-replete state. Contrary to expectation, calorie restriction enhanced basal and pulsatile LH secretion even further. As expected, plasma glucose, insulin, and leptin concentrations decreased by 18, 75, and 50%, respectively. Serum total testosterone concentration fell by 23%, whereas serum estrone, estradiol, sex hormone-binding globulin (SHBG), and androstenedione concentrations remained unchanged. Enhanced LH secretion in the presence of normal metabolic and hormonal adaptations to calorie restriction points to anomalous feedback control of pituitary LH release in PCOS.
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Affiliation(s)
- Eveline W C M Van Dam
- Department of Endocrinology, Leiden University Medical Center, 2300 RC Leiden, The Netherlands
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Abstract
Since its discovery in 1994, leptin, a protein hormone synthesized and secreted by adipose tissue, has been shown to regulate feed intake in several species including sheep and pigs. Although a nimiety of information exists regarding the physiological role of leptin in rodents and humans, the regulation and action of leptin in domestic animals is less certain. Emerging evidence in several species indicates that leptin may also affect the hypothalamo-pituitary-gonadal axis. Leptin receptor mRNA is present in the anterior pituitary and hypothalamus of several species, including sheep. In rats, effects of leptin on GnRH, LH and FSH secretion have been inconsistent, with leptin exhibiting both stimulatory and inhibitory action in vivo and in vitro. Evidence to support direct action of leptin at the level of the gonad indicates that the leptin receptor and its mRNA are present in ovarian tissue of several species, including cattle. These leptin receptors are functional, since leptin inhibits insulin-induced steroidogenesis of both granulosa and thecal cells of cattle in vitro. Leptin receptor mRNA is also found in the testes of rodents. As with the ovary, these receptors are functional, at least in rats, since leptin inhibits hCG-induced testosterone secretion by Leydig cells in vitro. During pregnancy, placental production of leptin may be a major contributor to the increase in maternal leptin in primates but not rodents. However, in both primates and rodents, leptin receptors exist in placental tissues and may regulate metabolism of the fetal-placental unit. As specific leptin immunoassays are developed for domestic animals, in vivo associations may then be made among leptin, body energy stores, dietary energy intake and reproductive function. This may lead to a more definitive role of leptin in domestic animal reproduction.
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Affiliation(s)
- L J Spicer
- Department of Animal Science, Oklahoma State University, Stillwater, Oklahoma 74078, USA.
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Peyon P, Zanuy S, Carrillo M. Action of leptin on in vitro luteinizing hormone release in the European sea bass (Dicentrarchus labrax). Biol Reprod 2001; 65:1573-8. [PMID: 11673277 DOI: 10.1095/biolreprod65.5.1573] [Citation(s) in RCA: 65] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/01/2022] Open
Abstract
The discovery of leptin has sparked a rapidly growing number of publications concerning the role of leptin in the regulation of body adiposity, feeding, and reproductive system in mammals. To date, there have been no reports on the presence of leptin-related peptide, and functional studies on the role of leptin remain limited in fishes. We investigated the effect of mouse recombinant leptin on basal and sea bream (sb) GnRH-induced LH release from dispersed pituitary cells obtained from male European sea bass (Dicentrarchus labrax) at different stages of sexual development. The potential interaction of leptin with the porcine neuropeptide Y (pNPY), known to play a dual role in feeding and reproduction in vertebrates, was also investigated. High doses of leptin (10(-8)-10(-6) M) and/or pNPY (0.1 and 1 nM) had different effects on LH release at various stages of sexual development. Porcine NPY alone was weakly effective on basal LH release, but it enhanced LH release induced by leptin (10(-6) M) in late prepuberty but not in early postpuberty. Additive or inhibitory effects of leptin were observed on sbGnRH-induced LH release depending on sbGnRH dose and stage of sexual development. The direct action of leptin on LH release at the pituitary level in sea bass suggests that leptin is a regulator of the reproductive system in fishes.
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Affiliation(s)
- P Peyon
- Department of Fish Reproductive Physiology, Instituto de Acuicultura de Torre de la Sal, Consejo Superior de Investigaciones Cientificas, 12595 Torre de la Sal, Castellon, Spain
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McCann SM, Karanth S, Mastronardi CA, Dees WL, Childs G, Miller B, Sower S, Yu WH. Control of gonadotropin secretion by follicle-stimulating hormone-releasing factor, luteinizing hormone-releasing hormone, and leptin. Arch Med Res 2001; 32:476-85. [PMID: 11750723 DOI: 10.1016/s0188-4409(01)00343-5] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Fractionation of hypothalamic extracts on a Sephadex G-25 column separates follicle-stimulating hormone-releasing factor (FSHRF) from luteinizing hormone-releasing hormone (LHRH). The FSH-releasing peak contained immunoreactive lamprey gonadotropin-releasing hormone (lGnRH) by radioimmunoassay, and its activity was inactivated by an antiserum specific to lGnRH. The identity of lGnRH-III with FSHRF is supported by studies with over 40 GnRH analogs that revealed that this is the sole analog with preferential FSH-releasing activity. Selective activity appears to require amino acids 5-8 of lGnRH-III. Chicken GnRH-II has slight selective FSH-releasing activity. Using a specific lGnRH-III antiserum, a population of lGnRH-III neurons was visualized in the dorsal and ventral preoptic area with axons projecting to the median eminence in areas shown previously to control FSH secretion based on lesion and stimulation studies. Some lGnRH-III neurons contained only this peptide, others also contained LHRH, and still others contained only LHRH. The differential pulsatile release of FSH and LH and their differential secretion at different times of the estrous cycle may be caused by differential secretion of FSHRF and LHRH. Both FSH and LHRH act by nitric oxide (NO) that generates cyclic guanosine monophosphate. lGnRH-III has very low affinity to the LHRH receptor. Biotinylated lGnRH-III (10(-9) M) labels 80% of FSH gonadotropes and is not displaced by LHRH, providing evidence for the existence of an FSHRF receptor. Leptin has equal potency as LHRH to release gonadotropins by NO. lGnRH-III specifically releases FSH, not only in rats but also in cows.
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Affiliation(s)
- S M McCann
- Department of Basic Science, Pennington Biomedical Research Center, Louisiana State University, Baton Rouge, LA 70808-3030, USA.
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McCann SM. Release of leptin and its effect on hormone release from human pituitary adenomas. Clin Endocrinol (Oxf) 2001; 55:161-2. [PMID: 11531921 DOI: 10.1046/j.1365-2265.2001.01338.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Affiliation(s)
- S M McCann
- Pennington Biomedical Research Center, 6400 Perkins Road, Baton Rouge, Louisiana 70808-4124, USA
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McCann SM, Kimura M, Karanth S, Yu WH, Mastronardi CA, Rettori V. The mechanism of action of cytokines to control the release of hypothalamic and pituitary hormones in infection. Ann N Y Acad Sci 2001; 917:4-18. [PMID: 11268367 DOI: 10.1111/j.1749-6632.2000.tb05368.x] [Citation(s) in RCA: 97] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
During infection, bacterial and viral products, such as bacterial lipopolysaccharide (LPS), cause the release of cytokines from immune cells. These cytokines can reach the brain by several routes. Furthermore, cytokines, such as interleukin-1 (IL-1), are induced in neurons within the brain by systemic injection of LPS. These cytokines determine the pattern of hypothalamic-pituitary secretion that characterizes infection. IL-2, by stimulation of cholinergic neurons, activates neural nitric oxide synthase (nNOS). The nitric oxide (NO) released diffuses into corticotropin-releasing hormone (CRH)-secreting neurons and releases CRH. IL-2 also acts in the pituitary to stimulate adrenocorticotropic hormone (ACTH) secretion. On the other hand, IL-1 alpha blocks the NO-induced release of luteinizing hormone-releasing hormone (LHRH) from LHRH neurons, thereby blocking pulsatile LH but not follicle-stimulating hormone (FSH) release and also inhibiting sex behavior that is induced by LHRH. IL-1 alpha and granulocyte macrophage colony-stimulating factor (GMCSF) block the response of the LHRH terminals to NO. The mechanism of action of GMCSF to inhibit LHRH release is as follows. It acts on its receptors on gamma-aminobutyric acid (GABA)ergic neurons to stimulate GABA release. GABA acts on GABAa receptors on the LHRH neuronal terminal to block NOergic stimulation of LHRH release. IL-1 alpha inhibits growth hormone (GH) release by inhibiting GH-releasing hormone (GHRH) release, which is mediated by NO, and stimulating somatostatin release, also mediated by NO. IL-1 alpha-induced stimulation of PRL release is also mediated by intrahypothlamic action of NO, which inhibits release of the PRL-inhibiting hormone dopamine. The actions of NO are brought about by its combined activation of guanylate cyclase-liberating cyclic guanosine monophosphate (cGMP) and activation of cyclooxygenase (COX) and lipoxygenase (LOX) with liberation of prostaglandin E2 and leukotrienes, respectively. Thus, NO plays a key role in inducing the changes in release of hypothalamic peptides induced in infection by cytokines. Cytokines, such as IL-1 beta, also act in the anterior pituitary gland, at least in part via induction of inducible NOS. The NO produced inhibits release of ACTH. The adipocyte hormone leptin, a member of the cytokine family, has largely opposite actions to those of the proinflammatory cytokines, stimulating the release of FSHRF and LHRH from the hypothalamus and FSH and LH from the pituitary directly by NO.
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Affiliation(s)
- S M McCann
- Pennington Biomedical Research Center (LSU), 6400 Perkins Road, Baton Rouge, LA 70808-4124, USA.
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Mastronardi CA, Walczewska A, Yu WH, Karanth S, Parlow AF, McCann SM. The possible role of prolactin in the circadian rhythm of leptin secretion in male rats. PROCEEDINGS OF THE SOCIETY FOR EXPERIMENTAL BIOLOGY AND MEDICINE. SOCIETY FOR EXPERIMENTAL BIOLOGY AND MEDICINE (NEW YORK, N.Y.) 2000; 224:152-8. [PMID: 10865230 DOI: 10.1046/j.1525-1373.2000.22414.x] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
In humans there is a circadian rhythm of leptin concentrations in plasma with a minimum in the early morning and a maximum in the middle of the night. By taking blood samples from adult male rats every 3 hr for 24 hr, we determined that a circadian rhythm of plasma leptin concentrations also occurs in the rat with a peak at 0130h and a minimum at 0730h. To determine if this rhythm is controlled by nocturnally released hormones, we evaluated the effect of hormones known to be released at night in humans, some of which are also known to be released at night in rats. In humans, prolactin (PRL), growth hormone (GH), and melatonin are known to be released at night, and adrenocorticotropic hormone (ACTH) release is inhibited. In these experiments, conscious rats were injected intravenously with 0.5 ml diluent or the substance to be evaluated just after removal of the first blood sample (0.3 ml), and additional blood samples (0.3 ml) were drawn every 10 min thereafter for 2 hr. The injection of highly purified sheep PRL (500 microg) produced a rapid increase in plasma leptin that persisted for the duration of the experiment. Lower doses were ineffective. To determine the effect of blockade of PRL secretion on leptin secretion, alpha bromoergocryptine (1.5 mg), a dopamine-2-receptor agonist that rapidly inhibits PRL release, was injected. It produced a rapid decline in plasma leptin within 10 min, and the decline persisted for 120 min. The minimal effective dose of GH to lower plasma leptin was 1 mg/rat. Insulin-like growth factor (IGF-1) (10 microg), but not IGF-2 (10 microg), also significantly decreased plasma leptin. Melatonin, known to be nocturnally released in humans and rats, was injected at a dose of 1 mg/rat during daytime (1100h) or nighttime (2300h). It did not alter leptin release significantly. Dexamethasone (DEX), a potent glucocorticoid, was ineffective at a 0. 1-mg dose but produced a delayed, significant increase in leptin, manifest 100-120 min after injection of a 1 mg dose. Since glucocorticoids decrease at night in humans at the time of the maximum plasma concentrations of leptin, we hypothesize that this increase in leptin from a relatively high dose of DEX would mimic the response to the release of corticosterone following stress in the rat and that glucocorticoids are not responsible for the circadian rhythm of leptin concentration. Therefore, we conclude that an increase in PRL secretion during the night may be responsible, at least in part, for the nocturnal elevation of leptin concentrations observed in rats and humans.
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Affiliation(s)
- C A Mastronardi
- Pennington Biomedical Research Center, Louisiana State University, Baton Rouge, Louisiana 70808-4124, USA
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McCann SM, Mastronardi C, Walczewska A, Karanth S, Rettori V, Yu WH. The role of nitric oxide in reproduction. Braz J Med Biol Res 1999; 32:1367-79. [PMID: 10559838 DOI: 10.1590/s0100-879x1999001100007] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Nitric oxide (NO) plays a crucial role in reproduction at every level in the organism. In the brain, it activates the release of luteinizing hormone-releasing hormone (LHRH). The axons of the LHRH neurons project to the mating centers in the brain stem and by afferent pathways evoke the lordosis reflex in female rats. In males, there is activation of NOergic terminals that release NO in the corpora cavernosa penis to induce erection by generation of cyclic guanosine monophosphate (cGMP). NO also activates the release of LHRH which reaches the pituitary and activates the release of gonadotropins by activating neural NO synthase (nNOS) in the pituitary gland. In the gonad, NO plays an important role in inducing ovulation and in causing luteolysis, whereas in the reproductive tract, it relaxes uterine muscle via cGMP and constricts it via prostaglandins (PG).
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Affiliation(s)
- S M McCann
- Pennington Biomedical Research Cente, Louisiana State University, Baton Rouge, LA 70808-4124, USA.
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