Ghrelin in the human myometrium
© O'Brien et al; licensee BioMed Central Ltd. 2010
Received: 29 March 2010
Accepted: 28 May 2010
Published: 28 May 2010
Ghrelin is a 28-amino acid octanolyated peptide, synthesised primarily in the stomach. It stimulates growth hormone release, food intake and exhibits many other diverse effects. Our group have previously determined that ghrelin inhibited human contractility in vitro. The aim of this study therefore, was to investigate the expression of ghrelin, its receptor, the growth hormone secretagogue receptor type 1 (GHS-R1), ghrelin O-acyltransferase (GOAT) which catalyses ghrelin octanoylation, prohormone convertase 1/3 (PC1/3) responsible for pro-ghrelin processing, in human myometrium, during pregnancy prior to labour, during labour and in the non-pregnant state. Modulation of ghrelin and ghrelin receptor expression in cultured myometrial cells was also investigated.
mRNA and protein were isolated from human myometrium and the myometrial smooth muscle cell line hTERT-HM; and real-time fluorescence RT-PCR, western blotting and fluorescence microscopy performed. The effects of β-Estradiol and bacterial lipopolysaccharide (LPS) on hTERT-HM gene expression were evaluated by western blotting.
We have reported for the first time the expression and processing of ghrelin, GHS-R1, GOAT and PC1/3 expression in human myometrium, and also the down-regulation of ghrelin mRNA and protein expression during labour. Furthermore, GHS-R1 protein expression significantly decreased at labour. Myometrial GOAT expression significantly increased during term non-labouring pregnancy in comparison to both non-pregnant and labouring myometrium. Mature PC1/3 protein expression was significantly decreased at term pregnancy and labour in comparison to non-pregnant myometrium. Ghrelin, GHS-R1, GOAT and PC1/3 mRNA and protein expression was also detected in the hTERT-HM cells. Ghrelin protein expression decreased upon LPS treatment in these cells while β-Estradiol treatment increased GHS-R1 expression.
Ghrelin processing occurred in the human myometrium at term pregnancy and in the non-pregnant state. GOAT expression which increased during term non-labouring pregnancy demonstrating a similar expression pattern to prepro-ghrelin and GHS-R1, decreased at labour, signifying possible myometrial ghrelin acylation. Moreover, the presence of PC1/3 may contribute to pro-ghrelin processing. These results along with the previous in vitro data suggest that myometrially-produced and processed ghrelin plays a significant autocrine or paracrine role in the maintenance of relaxation in this tissue during pregnancy. Furthermore, the significant uterine modulators LPS and β-Estradiol are involved in the regulation of ghrelin and ghrelin receptor expression respectively, in the human myometrium.
Ghrelin is an acylated 28-amino acid hormone  synthesised primarily in the stomach, it is also found in a wide range of other tissues including the hypothalamus, placenta, ovary, testis and endometrium [2, 3]. Ghrelin has an N-octanoyl group covalently linked to the hydroxyl group of its serine-3 residue, this modification being necessary for ghrelin to bind to its receptor, the growth hormone secretagogue receptor (GHS-R1) . No other naturally occurring peptide has been identified to have this post-translational acyl group modification . It is through the mediation of the seven transmembrane G-protein coupled receptor GHS-R1, coupled to the Gq subunit that ghrelin elicits growth hormone release, regulates appetite and energy metabolism and performs many functions in other tissues and organs, such as the reproductive system. In obese non-pregnant adults ghrelin levels are reduced but are increased in subjects of low body mass index . GHS-R1 is primarily expressed in the pituitary and the hypothalamus but is also widely expressed in many tissues including the stomach, testis, ovaries and endometrium [3, 7]. The enzyme that catalyses the octanoylation of ghrelin in the endoplasmic reticulum, is ghrelin O-acyltransferase (GOAT) [8, 9]. GOAT or mBOAT4 is a member of the family of membrane-bound O-acyltransferases. Des-acyl or unacylated ghrelin is the dominant form of ghrelin in the plasma, it cannot bind the GHS-R1 receptor but it has been suggested it plays alternative roles in a GHS-R1 independent pathway [5, 10].
The prepro-ghrelin protein is 117-amino acids in length: the signal peptide is cleaved to form the 94-amino acid pro-ghrelin peptide. A pro-hormone convertase 1/3 (PC1/3) is the only enzyme known to be responsible for the conversion of pro-ghrelin to ghrelin in vivo , it cleaves the 94-amino acid human ghrelin precursor into the 28-amino acid mature ghrelin, through proteolytic dibasic cleavage at the LQPR/ALAG site . PC1/3 is also capable of processing other hormones such as oxytocin , in dense core granules of the regulated secretory pathway .
In human pregnancy, total serum ghrelin levels peak around mid-gestation and fall to their lowest levels in the third trimester, and increase again postpartum [15, 16]. Acylated ghrelin levels were significantly increased in the 2nd, and decreased in the 3rd trimester compared to non-pregnant samples and samples taken during 1st trimester of pregnancy . Moreover, acylated ghrelin markedly decreased during pregnancy compared to the postpartum period . A previous report from our group highlighted that ghrelin had significant inhibitory effects on in vitro myometrial contractility .
Our aim therefore was to determine if ghrelin was expressed in the myometrium, and if so, investigate its regulation in this tissue during pregnancy. Firstly, we investigated ghrelin expression in the human myometrium during pregnancy, at term in labour (PL), term not in labour (PNL) and in the non-pregnant (NP) state. Secondly, the myometrial expression of GHS-R1, GOAT and PC1/3 was examined. Thirdly, we studied the effects of two compounds that regulate myometrial function, β-Estradiol and LPS, on ghrelin and GHS-R1 expression in a human myometrial smooth muscle cell line, hTERT-HM .
Biopsies of human myometrial tissue during pregnancy were obtained at elective (pregnant not in labour, PNL, i.e. prior to labour) and intrapartum (pregnant in labour, PL) caesarean section operations. The biopsies were excised from the upper lip of the lower uterine segment incision in the midline, i.e. the upper portion of the lower uterine segment. Women who had received prostaglandins or oxytocin for either induction or augmentation of labour were excluded from the study. Biopsies of human non-pregnant myometrial tissue (non-pregnant, NP) were obtained from pre-menopausal hysterectomy specimens, and women receiving therapy with progestagens, luteinising hormone-releasing hormone analogues, or steroid based medications were excluded from the study. Women with gynaecologic malignancy were also excluded from the study. Myometrial samples were carefully dissected to minimise decidual inclusion. Ethical Committee approval for the tissue collection procedure was obtained from the Research Ethics Committee University College Hospital, Galway and recruitment was by written informed consent. Immediately upon collection, tissue was snap-frozen in liquid nitrogen, and stored at -80°C.
Tissue samples for real-time fluorescence RT-PCR
Real time RT-PCR patient demographic data
NL (n= 3)
L (n= 3)
Mean Age at Delivery (years) +/- SEM
32.7 ± 1.8
33.7 ± 3.7
0: 1 woman
1: 2 women
≥ 2: 0 women
0: 1 woman
1: 1 woman
≥ 2: 1 woman
Mean Gestation Length (weeks) +/- SEM
38.7 ± 0.33
38.1 ± 1.1
Mean Baby Birth-weight (kg) +/- SEM
3.45 ± 0.06
3.7 ± 0.17
Tissue samples for protein expression
Western blot patient demographic data
NL (n= 5)
L (n= 6)
Mean Age at Delivery (years) +/- SEM
28.7 ± 1.9
35.2 ± 1.9
0: 0 women
1: 2 women
≥ 2: 3 women
0: 2 women
1: 4 women
≥ 2: 0 women
Mean Gestation Length (weeks) +/- SEM
38.2 ± 0.14
40.4 ± 0.3
Mean Baby Birth-weight (kg) +/- SEM
3.3 ± 0.1
3.85 ± 0.2
Human ghrelin (octanoylated), leptin, LPS, oxytocin, water soluble β-Estradiol and progesterone were purchased from Sigma (Dublin, Ireland).
Myometrial human telomerase reverse transcriptase (hTERT-HM) cells kindly provided by Dr. Jennifer C. Condon  were cultured in DMEM-F-12/10% FBS (Invitrogen, Carlsbad, CA, USA). Prior to treatment for western blotting, cells were pre-conditioned overnight in 2-10% charcoal stripped FBS (Biosera, East Sussex, UK) and phenol red free DMEM-F12 (Invitrogen, USA) and β-estradiol and LPS experiments performed in serum-free phenol red-free medium for 16 hours.
RNA extraction and reverse transcription
Total RNA was isolated from tissue using TRIzol reagent (Life Technologies Ltd., UK)  and cells using the RNeasy mini RNA isolation kit (Qiagen, Crawley, West Sussex, UK). RNA (1 μg- DNase I treated) was reverse transcribed for use as a template for Polymerase Chain Reaction (PCR). Samples in which no reverse transcriptase was added were included to confirm that no genomic DNA contamination was present.
Real time fluorescence PCR
Real time fluorescence PCR was performed using the Applied Biosystems StepOne Plus™ Real Time PCR System Relative Standard Curve method (ABI, Foster City, CA, USA) . The sequence of oligonucleotide primers (MWG, Ebersberg, Germany) for real time PCR were:
GHSR a and b
R1aR 5'- CACCACTACAGCCAGCATTTC-3'
R1bR 5'- GCTGAGACCCACCCAGCA-3' 
5'-AGTTGGTGACGATGCCGTG-3' (Accession M10277)
Each reaction was performed in triplicate. 2-tailed unpaired student t-tests were performed using Graphpad Prism 5 software (GraphPad Software, Inc., USA). P values < 0.05 were considered to be statistically significant.
Human myometrial tissue was homogenised and prepared as described previously .
Cell pellets after trypsinisation were washed in 1×PBS, centrifuged and re-suspended in ice-cold lysis buffer .
Western blot analysis
Proteins were resolved by SDS (w/v) polyacrylamide gel electrophoresis gels (BioRad, Hercules, CA, USA) as previously described . Membranes were blocked and incubated overnight at 4°C with 1/50-1/100 dilution of anti-human ghrelin rabbit polyclonal primary antibody (sc-50297), 1/100 dilution of ghrelin goat polyclonal (sc 10368), 1/100-1/200 GHS-R1 rabbit polyclonal (sc20748) (Santa Cruz Biotechnology Inc., Rockford, IL, USA), 1/500 GOAT rabbit (H-032-12) (Phoenix Pharmaceuticals Inc. Beach Road, Burlinghame, CA, USA), 1/500 PC1/3 mouse monoclonal (ab55543) (Abcam plc, Milton Road, Cambridge, UK) or 10,000 dilution of β-actin (ACTB) mouse monoclonal AC-15 (Sigma-Aldrich, Ireland) antibodies. Blots were washed and incubated in either 1:4,000 dilution of rabbit anti-goat (DakoCytomation Ltd, UK), 1:1000 goat anti-rabbit or 1:1000 dilution goat anti-mouse horseradish peroxidase-conjugated secondary antibodies (Pierce Technology, USA), the bound secondary antibody was detected as previously described . Statistical analysis of the densitometric data for each protein band compared to β-Actin (one way ANOVA with Tukey's post hoc analysis or 2-tailed unpaired student t-tests) and graph construction were performed using GraphPad Prism version 4 (GraphPad Software Inc., USA).
Cells were prepared as described previously and incubated with primary antibodies to ghrelin, GHS-R1, GOAT or PC1/3 .
Real time fluorescence RT-PCR-Tissue
Summary of tissue mRNA and protein densitometry data
Non-Pregnant (NP) (Densitometric value ± SEM)
Pregnant not in labour (PNL) (Densitometric value ± SEM)
Pregnant in labour (PL) (Densitometric value ± SEM)
Ghrelin mRNA (Figure 1)
0.733 ± 0.171
0.761 ± 0.058
0.164 ± 0.018
Ghrelin protein (Figure 2)
0.655 ± 0.094
0.557 ± 0.022
0.375 ± 0.049
0.349 ± 0.070
0.301 ± 0.039
0.352 ± 0.075
0.574 ± 0.061
0.457 ± 0.054
0.300 ± 0.091
Ghrelin protein (Figure 3)
1.578 ± 0.441
1.280 ± 0.092
0.521 ± 0.050
0.304 ± 0.068
0.677 ± 0.151
1.162 ± 0.421
GHS-R1 protein (Figure 4)
0.524 ± 0.053
0.589 ± 0.040
0.364 ± 0.054
GOAT protein (Figure 5)
0.428 ± 0.040
0.740 ± 0.073
0.311 ± 0.051
PC1/3 protein (Figure 6)
0.174 ± 0.049
0.061 ± 0.005
0.038 ± 0.004
GOAT and PC1/3
Ghrelin, GHS-R1, GOAT, PC1/3
This is the first report demonstrating the expression of ghrelin, GHS-R1, GOAT and PC1/3 in human myometrium. There was an increase in prepro-ghrelin and GOAT expression at pregnancy, decreasing at labour onset, while GHS-R1 also decreased at labour. Furthermore, ghrelin processing was demonstrated at term pregnancy and in the non-pregnant state, in the myometrium. Other investigators have determined that total and/or acylated ghrelin levels in blood peak at mid-gestation and fall to their lowest levels at the third trimester [15–18]. Ghrelin receptor GHS-R1a mRNA expression in omental fat of pregnant women at term was found to be half that of lean and obese non-pregnant women . Reduced ghrelin levels in third trimester maternal plasma have been hypothesised to be a response to marked changes in maternal energy intake . However we did not determine ghrelin acylation status in the myometrium or circulating ghrelin levels. We did investigate ghrelin, GHS-R1, GOAT and PC1/3 expression in a small number of women with high BMI values however, there did not seem to be any correlation between high BMI levels and the expression of any of these proteins in the human myometrium at term labour or term non-labour. Increased circulating ghrelin levels in foetuses with intrauterine growth restriction (IUGR) , increased maternal plasma ghrelin levels observed in pregnancy-induced hypertension (PIH) leading to IUGR  and higher umbilical cord ghrelin plasma concentrations in small-for-gestational-age (SGA) neonates  all suggest ghrelin acts as a "hunger signal", with a role in foetal and neonatal energy balance. Decreasing circulating ghrelin levels contribute to physiological adaptation to the positive energy balance of pregnancy and reflect the nutrition status of pregnancy while decreased expression of locally synthesised and processed ghrelin may be involved in the preparation of the myometrium for labour.
There are two GHS-R isoforms: GHS-R1a has 366-amino acids with seven transmembrane regions, and GHS-R1b, which consists of 289-amino acids and is not activated by ghrelin. In humans GHS-R1a is present in the pituitary, thyroid, pancreas, spleen, myocardium and adrenal gland while GHS-R1b expression is even more widely expressed including amongst others, the skin, uterine fundus, ovary, testes and placenta [3, 34]. Expression of mRNA for both GHS-R1a and b was identified in the myometrium, which had not been previously reported. GHS-R1 protein was localised to the cell surface and internally in vesicles. Other investigators previously established that GHS-R1 is recycled to the cell surface in HEK-293 cells after ghrelin binding and internalisation [35, 36]. We have established that GHS-R1 protein expression increased in β-Estradiol-treated estrogen receptor-positive myometrial smooth muscle cells. Ghrelin expression was also regulated by estrogen in rat stomach , while β-Estradiol significantly stimulated the transfected human GHS-R promoter in rat pituitary cells with estrogen-responsive elements identified in the promoter region . Estradiol-benzoate treatment of normal female or male rats up-regulated the expression of hypothalamic GHS-R1 . Therefore, it is postulated that β-Estradiol increases the sensitivity of the myometrium to ghrelin, through increased GHS-R1 expression, thus contributing to the maintenance of uterine relaxation during pregnancy.
Murine GOAT has been described in the stomach, small intestine and colon tissues while human GOAT mRNA is expressed in the stomach, intestine, pancreas and chrondrocytes [8, 9, 40]. This is the first report of GOAT expression in the uterus, where it appeared to localise in the myometrial smooth muscle cells. There was increased myometrial GOAT expression observed at term pregnancy and a similar pattern of GOAT protein expression to pro-ghrelin mRNA and protein at term compared to labour was observed, suggesting GOAT activation and possible ghrelin acylation during pregnancy. Interestingly, other investigators have found that murine stomach GOAT mRNA correlated with circulating acylated ghrelin levels . Yang et al. established that GOAT activity was inhibited by octanoylated ghrelin pentapeptides in GOAT-transfected insect cells, suggesting negative feedback regulation of acyl-ghrelin production , while in pituitary cells acylated ghrelin regulated its own production by increasing expression of GOAT mRNA . However, more investigation is required to ascertain the mechanisms of GOAT regulation in the myometrium and consequently the impact on myometrial ghrelin processing. From these results we can deduce that it is possible that myometrial ghrelin may be octanoylated by GOAT in this tissue.
In addition to endocrine and neuroendocrine cells, PC1/3 expression has been reported in rat spleen macrophages and lymphocytes  however, this is the first report of PC1/3 expression in the uterus, and also its subsequent activation. This endoprotease is responsible for the conversion of pro-ghrelin to ghrelin in vitro and in vivo  and it has also been demonstrated that production of n-octanoyl modified ghrelin in cultured cells requires PC1/3, GOAT and n-octanoic acid . Other investigators have demonstrated ghrelin and PC1/3 protein co-localisation in the mouse stomach . There was increased PC1/3 protein expression in the myometrial samples acquired at hysterectomy due to premenopausal menorrhagia, compared to the pregnant myometrial samples. Menorrhagia results in the disruption of normal hormonal uterine regulation and thus increased PC1/3 protein may be responsible for the irregular pro-hormone processing evident in this condition. Additional examination of the involvement of PC1/3 in non-pregnancy related uterine abnormalities is therefore warranted. The presence of active PC1/3 and mature ghrelin strongly indicates a role for PC1/3 in the proteolytic cleavage of pro-ghrelin in the myometrium. However, further investigation is necessary into this and its' own activation in the myometrium. Subsequent analysis may also reveal information relating to the processing of other pro-hormones by PC1/3 in the uterus.
Parturition at term is an inflammatory process and intra-amniotic infection/inflammation is causally linked to preterm parturition . Systemic administration of bacterial products to pregnant animals results in preterm delivery . We have demonstrated that LPS administration decreased myometrial smooth muscle cell ghrelin protein. Interestingly, the bacterial polysaccharide LPS decreased plasma ghrelin protein levels from 3 to 12 hrs after administration in rats [47, 48], and in healthy men induced an initial increase but rapidly decreased 5 hours after treatment . Ghrelin itself exerts potent inhibitory effects on proinflammatory mediators via its actions on T cells, monocytes and endothelial cells [50–52]. In human endothelial cells it inhibits NF-κB activation in vitro and endotoxin-induced cytokine production in vivo . Ghrelin inhibits the expression of Il-1β, IL-6 and TNF-α via GHS-R in human T cells while it's knockdown activates IκB in these cells, suggesting ghrelin plays a role in regulation of NF-κB activation [53, 54]. This is significant given that NF-κB is a key transcription factor important in the regulation of inflammation, which plays a central role at labour . The 5' upstream region from the start codon of the ghrelin gene contains 2 binding sites for NF-κB suggesting a possible feedback loop. Interestingly, the PC1/3 gene also contains two 2 putative NF-κB binding sites. As ghrelin has anti-inflammatory properties, decreasing ghrelin levels would enhance the overall inflammatory pathway occurring at labour. However, further work is necessary to determine if ghrelin is involved in NF-κB modulation and vice versa, in human myometrium.
All the necessary machinery to produce active ghrelin is present in the myometrium, suggesting ghrelin may have an autocrine or paracrine effect in this tissue. Differential ghrelin gene expression at term pregnancy, the presence of ghrelin-processing enzymes and the in vitro contractility data indicates that it may play a role in the maintenance of uterine relaxation during pregnancy, and that at labour this inhibitory effect on myometrial contractility is down-regulated. Reduced local myometrial ghrelin production therefore may be involved in the preparation of the uterus for labour.
Furthermore, the regulation of ghrelin expression by significant modulators of myometrial contractility, β-Estradiol and bacterial lipopolysaccharide, represents a novel concept in terms of control of myometrial quiescience or activity during pregnancy, and at the time of labour. Finally, it is possible that pharmacological modulation of the ghrelin pathway in uterine smooth muscle may have future therapeutic potential.
MOB: PhD. PE: MSc. Professor JJM: MB BCh, BSc. DCH, FRCOG, FRCPI consultant obstetrician and gynaecologist, chairman and head of the Department of Obstetrics and Gynaecology in UCHG, Galway. Professor TJS: PhD, vice-president for Research in NUI Galway.
The authors are grateful to the medical and midwifery staff at University College Hospital Galway for their assistance with patient recruitment and tissue collection. The authors thank Dr. Jennifer C. Condon for provision of the hTERT-HM myometrial smooth muscle cells. This study was funded by the Health Research Board of Ireland, the Higher Education Authority of Ireland's Program for Research in Third Level Institutions and National University of Ireland, Galway.
- Kojima M, Hosoda H, Date Y, Nakazato M, Matsuo H, Kangawa K: Ghrelin is a growth-hormone-releasing acylated peptide from stomach. Nature. 1999, 402 (6762): 656-660. 10.1038/45230.View ArticlePubMed
- Tanaka K, Minoura H, Isobe T, Yonaha H, Kawato H, Wang DF, Yoshida T, Kojima M, Kangawa K, Toyoda N: Ghrelin is involved in the decidualization of human endometrial stromal cells. J Clin Endocrinol Metab. 2003, 88 (5): 2335-2340. 10.1210/jc.2002-021024.View ArticlePubMed
- Gnanapavan S, Kola B, Bustin SA, Morris DG, McGee P, Fairclough P, Bhattacharya S, Carpenter R, Grossman AB, Korbonits M: The tissue distribution of the mRNA of ghrelin and subtypes of its receptor, GHS-R, in humans. J Clin Endocrinol Metab. 2002, 87 (6): 2988-10.1210/jc.87.6.2988.View ArticlePubMed
- Kojima M, Kangawa K: Ghrelin: structure and function. Physiol Rev. 2005, 85 (2): 495-522. 10.1152/physrev.00012.2004.View ArticlePubMed
- Korbonits M, Goldstone AP, Gueorguiev M, Grossman AB: Ghrelin--a hormone with multiple functions. Front Neuroendocrinol. 2004, 25 (1): 27-68. 10.1016/j.yfrne.2004.03.002.View ArticlePubMed
- Soriano-Guillen L, Barrios V, Campos-Barros A, Argente J: Ghrelin levels in obesity and anorexia nervosa: effect of weight reduction or recuperation. J Pediatr. 2004, 144 (1): 36-42. 10.1016/j.jpeds.2003.10.036.View ArticlePubMed
- Tawadros N, Salamonsen LA, Dimitriadis E, Chen C: Facilitation of decidualization by locally produced ghrelin in the human endometrium. Mol Hum Reprod. 2007, 13 (7): 483-489. 10.1093/molehr/gam029.View ArticlePubMed
- Yang J, Brown MS, Liang G, Grishin NV, Goldstein JL: Identification of the acyltransferase that octanoylates ghrelin, an appetite-stimulating peptide hormone. Cell. 2008, 132 (3): 387-396. 10.1016/j.cell.2008.01.017.View ArticlePubMed
- Gutierrez JA, Solenberg PJ, Perkins DR, Willency JA, Knierman MD, Jin Z, Witcher DR, Luo S, Onyia JE, Hale JE: Ghrelin octanoylation mediated by an orphan lipid transferase. Proc Natl Acad Sci USA. 2008, 105 (17): 6320-6325. 10.1073/pnas.0800708105.PubMed CentralView ArticlePubMed
- Hosoda H, Kojima M, Matsuo H, Kangawa K: Ghrelin and des-acyl ghrelin: two major forms of rat ghrelin peptide in gastrointestinal tissue. Biochem Biophys Res Commun. 2000, 279 (3): 909-913. 10.1006/bbrc.2000.4039.View ArticlePubMed
- Zhu X, Cao Y, Voogd K, Steiner DF: On the processing of proghrelin to ghrelin. J Biol Chem. 2006, 281 (50): 38867-38870. 10.1074/jbc.M607955200.View ArticlePubMed
- Ozawa A, Cai Y, Lindberg I: Production of bioactive peptides in an in vitro system. Anal Biochem. 2007, 366 (2): 182-189. 10.1016/j.ab.2007.04.020.PubMed CentralView ArticlePubMed
- Vandesande F, Dierickx K: Identification of the vasopressin producing and of the oxytocin producing neurons in the hypothalamic magnocellular neurosecretroy system of the rat. Cell Tissue Res. 1975, 164 (2): 153-162. 10.1007/BF00218970.View ArticlePubMed
- Dikeakos JD, Mercure C, Lacombe MJ, Seidah NG, Reudelhuber TL: PC1/3, PC2 and PC5/6A are targeted to dense core secretory granules by a common mechanism. FEBS J. 2007, 274 (16): 4094-4102. 10.1111/j.1742-4658.2007.05937.x.View ArticlePubMed
- Makino Y, Hosoda H, Shibata K, Makino I, Kojima M, Kangawa K, Kawarabayashi T: Alteration of plasma ghrelin levels associated with the blood pressure in pregnancy. Hypertension. 2002, 39 (3): 781-784. 10.1161/hy0302.105221.View ArticlePubMed
- Fuglsang J, Skjaerbaek C, Espelund U, Frystyk J, Fisker S, Flyvbjerg A, Ovesen P: Ghrelin and its relationship to growth hormones during normal pregnancy. Clin Endocrinol (Oxf). 2005, 62 (5): 554-559. 10.1111/j.1365-2265.2005.02257.x.View Article
- Palik E, Baranyi E, Melczer Z, Audikovszky M, Szocs A, Winkler G, Cseh K: Elevated serum acylated (biologically active) ghrelin and resistin levels associate with pregnancy-induced weight gain and insulin resistance. Diabetes Res Clin Pract. 2007, 76 (3): 351-357. 10.1016/j.diabres.2006.09.005.View ArticlePubMed
- Tham E, Liu J, Innis S, Thompson D, Gaylinn BD, Bogarin R, Haim A, Thorner MO, Chanoine JP: Acylated ghrelin concentrations are markedly decreased during pregnancy in mothers with and without gestational diabetes: relationship with cholinesterase. Am J Physiol Endocrinol Metab. 2009, 296 (5): E1093-1100. 10.1152/ajpendo.90866.2008.PubMed CentralView ArticlePubMed
- Hehir MP, Glavey SV, Morrison JJ: Uterorelaxant effect of ghrelin on human myometrial contractility. Am J Obstet Gynecol. 2008, 198 (3): 323 e321-325.
- Condon J, Yin S, Mayhew B, Word RA, Wright WE, Shay JW, Rainey WE: Telomerase immortalization of human myometrial cells. Biol Reprod. 2002, 67 (2): 506-514. 10.1095/biolreprod67.2.506.View ArticlePubMed
- Chomczynski P: A reagent for the single-step simultaneous isolation of RNA, DNA and proteins from cell and tissue samples. Biotechniques. 1993, 15 (3): 532-534. 536-537PubMed
- Fitzgibbon J, Morrison JJ, Smith TJ, O'Brien M: Modulation of human uterine smooth muscle cell collagen contractility by thrombin, Y-2763, TNF alpha and indomethacin. Reprod Biol Endocrinol. 2009, 7: 10.1186/1477-7827-7-2.
- Gualillo O, Caminos J, Blanco M, Garcia-Caballero T, Kojima M, Kangawa K, Dieguez C, Casanueva F: Ghrelin, a novel placental-derived hormone. Endocrinology. 2001, 142 (2): 788-794. 10.1210/en.142.2.788.PubMed
- Hattori N, Saito T, Yagyu T, Jiang BH, Kitagawa K, Inagaki C: GH, GH receptor, GH secretagogue receptor, and ghrelin expression in human T cells, B cells, and neutrophils. J Clin Endocrinol Metab. 2001, 86 (9): 4284-4291. 10.1210/jc.86.9.4284.View ArticlePubMed
- Korbonits M, Bustin SA, Kojima M, Jordan S, Adams EF, Lowe DG, Kangawa K, Grossman AB: The expression of the growth hormone secretagogue receptor ligand ghrelin in normal and abnormal human pituitary and other neuroendocrine tumors. J Clin Endocrinol Metab. 2001, 86 (2): 881-887. 10.1210/jc.86.2.881.PubMed
- Freyer C, Kilpatrick LM, Salamonsen LA, Nie G: Pro-protein convertases (PCs) other than PC6 are not tightly regulated for implantation in the human endometrium. Reproduction. 2007, 133 (6): 1189-1197. 10.1530/REP-06-0285.View ArticlePubMed
- O'Brien M, Morrison JJ, Smith TJ: Expression of prothrombin and protease activated receptors in human myometrium during pregnancy and labor. Biol Reprod. 2008, 78 (1): 20-26. 10.1095/biolreprod.107.062182.View ArticlePubMed
- Condon JC, Hardy DB, Kovaric K, Mendelson CR: Up-regulation of the progesterone receptor (PR)-C isoform in laboring myometrium by activation of nuclear factor-kappaB may contribute to the onset of labor through inhibition of PR function. Mol Endocrinol. 2006, 20 (4): 764-775. 10.1210/me.2005-0242.View ArticlePubMed
- O'Brien M, Flynn D, Mullins B, Morrison JJ, Smith TJ: Expression of RHOGTPase regulators in human myometrium. Reprod Biol Endocrinol. 2008, 6: 1-10.1186/1477-7827-6-1.PubMed CentralView ArticlePubMed
- Fontenot E, DeVente JE, Seidel ER: Obestatin and ghrelin in obese and in pregnant women. Peptides. 2007, 28 (10): 1937-1944. 10.1016/j.peptides.2007.08.005.View ArticlePubMed
- Lorenzi T, Meli R, Marzioni D, Morroni M, Baragli A, Castellucci M, Gualillo O, Muccioli G: Ghrelin: a metabolic signal affecting the reproductive system. Cytokine Growth Factor Rev. 2009, 20 (2): 137-152. 10.1016/j.cytogfr.2009.02.003.View ArticlePubMed
- Cortelazzi D, Cappiello V, Morpurgo PS, Ronzoni S, Nobile De Santis MS, Cetin I, Beck-Peccoz P, Spada A: Circulating levels of ghrelin in human fetuses. Eur J Endocrinol. 2003, 149 (2): 111-116. 10.1530/eje.0.1490111.View ArticlePubMed
- Farquhar J, Heiman M, Wong AC, Wach R, Chessex P, Chanoine JP: Elevated umbilical cord ghrelin concentrations in small for gestational age neonates. J Clin Endocrinol Metab. 2003, 88 (9): 4324-4327. 10.1210/jc.2003-030265.View ArticlePubMed
- Depoortere I: Targeting the ghrelin receptor to regulate food intake. Regul Pept. 2009, 156 (1-3): 13-23. 10.1016/j.regpep.2009.04.002.View ArticlePubMed
- Camina JP, Carreira MC, El Messari S, Llorens-Cortes C, Smith RG, Casanueva FF: Desensitization and endocytosis mechanisms of ghrelin-activated growth hormone secretagogue receptor 1a. Endocrinology. 2004, 145 (2): 930-940. 10.1210/en.2003-0974.View ArticlePubMed
- Holliday ND, Holst B, Rodionova EA, Schwartz TW, Cox HM: Importance of constitutive activity and arrestin-independent mechanisms for intracellular trafficking of the ghrelin receptor. Mol Endocrinol. 2007, 21 (12): 3100-3112. 10.1210/me.2007-0254.View ArticlePubMed
- Matsubara M, Sakata I, Wada R, Yamazaki M, Inoue K, Sakai T: Estrogen modulates ghrelin expression in the female rat stomach. Peptides. 2004, 25 (2): 289-297. 10.1016/j.peptides.2003.12.020.View ArticlePubMed
- Petersenn S, Rasch AC, Penshorn M, Beil FU, Schulte HM: Genomic structure and transcriptional regulation of the human growth hormone secretagogue receptor. Endocrinology. 2001, 142 (6): 2649-2659. 10.1210/en.142.6.2649.PubMed
- Carmignac DF, Bennett PA, Robinson IC: Effects of growth hormone secretagogues on prolactin release in anesthetized dwarf (dw/dw) rats. Endocrinology. 1998, 139 (8): 3590-3596. 10.1210/en.139.8.3590.PubMed
- Gomez R, Lago F, Gomez-Reino JJ, Dieguez C, Gualillo O: Expression and modulation of ghrelin O-acyltransferase in cultured chondrocytes. Arthritis Rheum. 2009, 60 (6): 1704-1709. 10.1002/art.24522.View ArticlePubMed
- Gahete MD, Cordoba-Chacon J, Salvatori R, Castano JP, Kineman RD, Luque RM: Metabolic regulation of ghrelin O-acyl transferase (GOAT) expression in the mouse hypothalamus, pituitary, and stomach. Mol Cell Endocrinol. 317 (1-2): 154-160. 10.1016/j.mce.2009.12.023.
- Yang J, Zhao TJ, Goldstein JL, Brown MS: Inhibition of ghrelin O-acyltransferase (GOAT) by octanoylated pentapeptides. Proc Natl Acad Sci USA. 2008, 105 (31): 10750-10755. 10.1073/pnas.0805353105.PubMed CentralView ArticlePubMed
- Lansac G, Dong W, Dubois CM, Benlarbi N, Afonso C, Fournier I, Salzet M, Day R: Lipopolysaccharide mediated regulation of neuroendocrine associated proprotein convertases and neuropeptide precursor processing in the rat spleen. J Neuroimmunol. 2006, 171 (1-2): 57-71. 10.1016/j.jneuroim.2005.09.019.View ArticlePubMed
- Takahashi T, Ida T, Sato T, Nakashima Y, Nakamura Y, Tsuji A, Kojima M: Production of n-octanoyl-modified ghrelin in cultured cells requires prohormone processing protease and ghrelin O-acyltransferase, as well as n-octanoic acid. J Biochem. 2009
- Romero R, Espinoza J, Goncalves LF, Kusanovic JP, Friel LA, Nien JK: Inflammation in preterm and term labour and delivery. Semin Fetal Neonatal Med. 2006, 11 (5): 317-326. 10.1016/j.siny.2006.05.001.View ArticlePubMed
- Elovitz MA, Wang Z, Chien EK, Rychlik DF, Phillippe M: A new model for inflammation-induced preterm birth: the role of platelet-activating factor and Toll-like receptor-4. Am J Pathol. 2003, 163 (5): 2103-2111.PubMed CentralView ArticlePubMed
- Hataya Y, Akamizu T, Hosoda H, Kanamoto N, Moriyama K, Kangawa K, Takaya K, Nakao K: Alterations of plasma ghrelin levels in rats with lipopolysaccharide-induced wasting syndrome and effects of ghrelin treatment on the syndrome. Endocrinology. 2003, 144 (12): 5365-5371. 10.1210/en.2003-0427.View ArticlePubMed
- Basa NR, Wang L, Arteaga JR, Heber D, Livingston EH, Tache Y: Bacterial lipopolysaccharide shifts fasted plasma ghrelin to postprandial levels in rats. Neurosci Lett. 2003, 343 (1): 25-28. 10.1016/S0304-3940(03)00312-4.View ArticlePubMed
- Vila G, Maier C, Riedl M, Nowotny P, Ludvik B, Luger A, Clodi M: Bacterial endotoxin induces biphasic changes in plasma ghrelin in healthy humans. J Clin Endocrinol Metab. 2007, 92 (10): 3930-3934. 10.1210/jc.2007-1194.View ArticlePubMed
- Dixit VD, Schaffer EM, Pyle RS, Collins GD, Sakthivel SK, Palaniappan R, Lillard JW, Taub DD: Ghrelin inhibits leptin- and activation-induced proinflammatory cytokine expression by human monocytes and T cells. J Clin Invest. 2004, 114 (1): 57-66.PubMed CentralView ArticlePubMed
- Gonzalez-Rey E, Chorny A, Delgado M: Therapeutic action of ghrelin in a mouse model of colitis. Gastroenterology. 2006, 130 (6): 1707-1720. 10.1053/j.gastro.2006.01.041.View ArticlePubMed
- Li WG, Gavrila D, Liu X, Wang L, Gunnlaugsson S, Stoll LL, McCormick ML, Sigmund CD, Tang C, Weintraub NL: Ghrelin inhibits proinflammatory responses and nuclear factor-kappaB activation in human endothelial cells. Circulation. 2004, 109 (18): 2221-2226. 10.1161/01.CIR.0000127956.43874.F2.View ArticlePubMed
- Dixit VD, Yang H, Cooper-Jenkins A, Giri BB, Patel K, Taub DD: Reduction of T cell-derived ghrelin enhances proinflammatory cytokine expression: implications for age-associated increases in inflammation. Blood. 2009, 113 (21): 5202-5205. 10.1182/blood-2008-09-181255.PubMed CentralView ArticlePubMed
- Kishimoto M, Okimura Y, Nakata H, Kudo T, Iguchi G, Takahashi Y, Kaji H, Chihara K: Cloning and characterization of the 5(')-flanking region of the human ghrelin gene. Biochem Biophys Res Commun. 2003, 305 (1): 186-192. 10.1016/S0006-291X(03)00722-8.View ArticlePubMed
- Mendelson CR, Hardy DB: Role of the progesterone receptor (PR) in the regulation of inflammatory response pathways and aromatase in the breast. J Steroid Biochem Mol Biol. 2006, 102 (1-5): 241-249. 10.1016/j.jsbmb.2006.09.029.PubMed CentralView ArticlePubMed
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.