Gastric Peptide Ghrelin Research Articles

The role of serum gastric peptide ghrelin hormone level in irritable bowel syndrome at Zagazig University Hospitals

Generalized dysmotility of the gastrointestinal tract develops in individuals with irritable bowel syndrome (IBS). The ghrelin hormone appears to be critical in controlling gastrointestinal motility. We aimed to evaluate serum ghrelin levels in people with IBS and to demonstrate its role in IBS pathophysiology. This study included 32 individuals with IBS (16 with constipation and 16 with diarrhea) and 16 healthy individuals as controls. Blood specimens were collected from patients and controls following an overnight fast. Total ghrelin level was detected in plasma by commercially available ELISA Kit. There were significant differences in the serum levels of ghrelin between the control group and both types of IBS. The mean±SD of ghrelin level in the control group was 2.608±0.714 pg/ml, and that of both types of IBS was 5.782±2.450 pg/ml (P-value<0.001). There was a significant variation between the control and IBS-D groups (mean±SD: 7.838±1.687 pg/ml, p-value<0.001). Also, we indicated a considerable difference between the control and IBS-C groups (mean±SD: 3.726±0.740 pg/ml, P-value<0.001). In comparing the IBS-D group and IBS-C group, we found a highly considerable variation between the two groups (p-value<0.001). This means that serum ghrelin levels were significantly greater in IBS-D than in IBS-C and the control group. Our findings concluded that serum ghrelin level was higher among the IBS-D group than in the IBS-C and control groups. The ghrelin hormone may play a vital role in IBS pathophysiology.

Grelin ve Grelin Reseptörü Polimorfizmlerinin Tip 2 Diyabetle İlişkisi

Bir gastrik peptit olan grelin ve onun büyüme hormonu salgılatıcı G protein-bağlı reseptörünün glukoz metabolizması ve enerji homeostazında önemli bir rol oynadığına dair ciddi kanıtlar mevcuttur. Bu nedenle, Tip 2 diyabet için duyarlılık alelleri taşıyan bu genler potansiyel birer aday olarak değerlendirilmektedir. Isparta yöresinden 75 Tip 2 diyabet hastası ve 25 kontrolden oluşan 100 Türk yetişkin bireyin dahil edildiği vaka-kontrol kesitsel ilişkilendirme çalışması yapıldı. Grelin geninde dört promotör (rs26311, rs26312, rs27647, rs3755777) ve bir intronik (rs35683) bölge ve Grelin reseptöründe bir intronik (rs509035) ve bir 3'UTR (rs565105) bölge tek nükleotid polimorfizmleri seçilerek Tip 2 diyabet ile ilişkisi Matris Destekli Lazer Desorpsiyon/İyonizasyon Uçuş Süresi Kütle Spektrometresi sistemi kullanılarak araştırıldı. Tip 2 diyabet ile iki adet tek nükleotid polimorfizmi arasında anlamlı bir ilişki saptandı: Grelin geninin promotör bölgesinde yer alan rs27647 ve intron 1'de bulunan rs35683 (P&amp;lt;0.05). Sonuç olarak, elde edilen bulgular Isparta yöresinde yaşayan Tip 2 diyabet toplumunda grelin polimorfizmlerinin hastalık gelişimine yatkınlık oluşturabileceğini düşündürmektedir.

Unusual orthologs shed new light on the binding mechanism of ghrelin to its receptor GHSR1a

The gastric peptide ghrelin has important functions in energy metabolism and cellular homeostasis by activating growth hormone secretagogue receptor type 1a (GHSR1a). The N-terminal residues of ghrelin orthologs from all vertebrates are quite conserved; however, in orthologs from Cavia porcellus and Phyllostomus discolor, Ser2 and Leu5 are replaced by a smaller Ala and a positively charged Arg, respectively. In the present study, we first demonstrated that the hydrophobic Leu5 is essential for the function of human ghrelin, because Ala replacement caused an approximately 100-fold decrease in activity. However, replacement of Leu5 by an Arg residue caused much less disruption; further replacement of Ser2 by Ala almost restored full activity, although the [S2A] mutation itself showed slight detriments, implying that the positively charged Arg5 in the [S2A,L5R] mutant might form alternative interactions with certain receptor residues to compensate for the loss of the essential Leu5. To identify the responsible receptor residues, we screened GHSR1a mutants in which all conserved negatively charged residues in the extracellular regions and all aromatic residues in the ligand-binding pocket were mutated separately. According to the decrease in selectivity of the mutant receptors towards [S2A,L5R]ghrelin, we deduced that the positively charged Arg5 of the ghrelin mutant primarily interacts with the essential aromatic Phe286 at the extracellular end of the sixth transmembrane domain of GHSR1a by forming cation−π and π−π interactions. The present study provided new insights into the binding mechanism of ghrelin with its receptor, and thus would facilitate the design of novel ligands for GHSR1a.

Identifying key residues and key interactions for the binding of LEAP2 to receptor GHSR1a.

Liver-expressed antimicrobial peptide 2 (LEAP2) was recently identified as a competitive antagonist for the G protein-coupled receptor GHSR1a, the cognate receptor for the gastric peptide ghrelin. LEAP2 plays important functions in energy metabolism by tuning the ghrelin-GHSR1a system. However, the molecular mechanism by which LEAP2 binds to GHSR1a is largely unknown. In the present study, we first conducted alanine-scanning mutagenesis on the N-terminal fragment of human LEAP2 and demonstrated that the positively charged Arg6 and the aromatic Phe4 are essential for LEAP2 binding to GHSR1a. To identify the receptor residues interacting with the essential Arg6 and Phe4 of LEAP2, we conducted extensive site-directed mutagenesis on GHSR1a. After all conserved negatively charged residues in the extracellular regions of human GHSR1a were mutated, only mutation of Asp99 caused much more detriments to GHSR1a binding to LEAP2 than binding to ghrelin, suggesting that the absolutely conserved Asp99 of GHSR1a probably interacts with the essential Arg6 of LEAP2. After five conserved Phe residues in the predicted ligand-binding pocket of human GHSR1a were mutated, three of them were identified as important for GHSR1a binding to LEAP2. According to a structural model of GHSR1a, we deduced that the adjacent Phe279 and Phe312 might interact with the essential Phe4 of LEAP2, while Phe119 might interact with the aromatic Trp5 of LEAP2. The present study provided new insights into the interaction of LEAP2 with its receptor, and would facilitate the design of novel ligands for GHSR1a in future studies.

Identifying the binding mechanism of LEAP2 to receptor GHSR1a.

Liver-expressed antimicrobial peptide 2 (LEAP2) is a highly conserved secretory peptide first isolated in 2003. However, its exact biological functions remained elusive until a recent study identified it as an endogenous antagonist for the growth hormone secretagogue receptor (GHSR1a), a G protein-coupled receptor for which the gastric peptide ghrelin is the endogenous agonist. By tuning the ghrelin-GHSR1a system, LEAP2 has an important function in energy metabolism. In the present study, we first demonstrated that LEAP2 and ghrelin actually bound to GHSR1a in a competitive manner, rather than in a non-competitive manner as previously reported, by binding assays and activation assays. Subsequently, we demonstrated that the antagonistic function of LEAP2 was drastically affected by the manner of its addition. LEAP2 primarily affected the maximal activation effect when added before ghrelin, whereas it primarily affected half-maximal effective concentration when added at the same time as ghrelin. Thus, LEAP2 behaved as a competitive antagonist if added at the same time as the agonist and a non-competitive antagonist if added before the agonist. This unusual property of LEAP2 might be caused by its slow dissociation from receptor GHSR1a. We also found that the N-terminal fragment of LEAP2 was important for receptor binding. Our present study revealed an antagonistic mechanism for LEAP2, and will facilitate the design of novel antagonists for receptor GHSR1a in future studies.

Ghrelin and hypothalamic development: too little and too much of a good thing.

Neural centers in the hypothalamus regulate food intake and body weight in response to hormones and other neural stimuli, and dysfunctional communication between the brain and gut underlies metabolic disorders, including obesity. In this issue of the JCI, Steculorum and colleagues present evidence that the gastric peptide ghrelin mediates neural fiber growth in the arcuate nucleus of the hypothalamus during the neonatal period. Neonatal mice subjected to either increased or decreased ghrelin action during this developmental period had an increased risk of obesity in adulthood. Together, the results of this study support a model whereby neural organization at key stages of development sets the foundation for metabolic health later in life.

The Acute Salivary Ghrelin Response to a Psychosocial Stress Is Enhanced in Symptomatic Patients with Bulimia Nervosa: A Pilot Study

Background: Stress is a precipitating factor for both binge eating and bulimia nervosa (BN); however, the biological mechanisms through which it may trigger binge eating are poorly understood. There is evidence that the adrenal hormone cortisol and the gastric peptide ghrelin might be involved in stress-induced food ingestion. We hypothesized that symptomatic patients with BN might disclose deranged responses of ghrelin and/or cortisol to stressors and that this could be related to their binge-eating behaviour. Methods: Here we investigated salivary cortisol and ghrelin responses to the Trier Social Stress Test (TSST) in 10 women with acute BN and 10 age-matched healthy females. Eating-related psychopathology and behaviours were assessed by self-report measures. Results: No significant differences emerged between bulimic patients and healthy controls in the pre-stress salivary levels of both cortisol and ghrelin. The BN patients displayed normal cortisol but enhanced ghrelin responses to TSST. No significant correlations emerged between stress-induced salivary hormone changes and self-report measures of binge eating. Conclusion: To our knowledge, this is the first study showing deranged salivary ghrelin reactivity to a psychosocial stressor in symptomatic patients with BN. The extent to which this could contribute to the binge-eating behaviour of BN subjects awaits clarification.

Testing for growth hormone deficiency in adults

This article summarizes recent advances in testing for growth hormone deficiency (GHD) in adults, focusing on critical appraisal of existing growth hormone (GH) provocative tests as well as newer tests in development. The diagnosis of GHD can be challenging and often requires the use of GH provocative testing. The most widely validated of these is insulin-induced hypoglycemia (ITT), which requires close supervision and has significant contraindications and side-effects. The arginine-growth hormone-releasing hormone (GHRH) test had become widely used as a safe and accurate alternative to the ITT, but GHRH is currently unavailable for clinical use in the USA. On the basis of review of recent literature we recommend that in the absence of GHRH, glucagon stimulation testing should be the preferred alternative to ITT. Several synthetic GH secretagogues that mimic the gastric peptide ghrelin are currently in development and may become available for use in the diagnosis of GHD in the near future. Other GH provocative tests suitable for use in children lack adequate specificity for the diagnosis of GHD in adults. Due to the current unavailability of the arginine-GHRH test in the USA, when ITT is contraindicated or impractical we recommend the glucagon stimulation testing as the GH provocative test of choice. There remains a need for a simple, safe and accurate test for the diagnosis of GHD.

Ghrelin protects musculocutaneous tissue from ischemic necrosis by improving microvascular perfusion

Persistent ischemia in musculocutaneous tissue may lead to wound breakdown and necrosis. The objective of this experimental study was to analyze, whether the gastric peptide ghrelin prevents musculocutaneous tissue from necrosis and to elucidate underlying mechanisms. Thirty-two C57BL/6 mice equipped with a dorsal skinfold chamber containing ischemic musculocutaneous tissue were allocated to four groups: 1) ghrelin; 2) N(ω)-nitro-l-arginine methyl ester (l-NAME); 3) ghrelin and l-NAME; and 4) control. Microcirculation, inflammation, angiogenesis, and tissue survival were assessed by fluorescence microscopy. Inducible and endothelial nitric oxide synthase (iNOS I and eNOS), vascular endothelial growth factor (VEGF), as well as nuclear factor κB (NF-κB) were assessed by Western blot analysis. Ghrelin-treated animals showed an increased expression of iNOS and eNOS in critically perfused tissue compared with controls. This was associated with arteriolar dilation, increased arteriolar perfusion, and a sustained functional capillary density. Ghrelin further upregulated NF-κB and VEGF and induced angiogenesis. Finally, ghrelin reduced microvascular leukocyte-endothelial cell interactions, apoptosis, and overall tissue necrosis (P < 0.05 vs. control). Inhibition of nitric oxide by l-NAME did not affect the anti-inflammatory and angiogenic action of ghrelin but completely blunted the ghrelin-induced tissue protection by abrogating the arteriolar dilation, the improved capillary perfusion, and the increased tissue survival. Ghrelin prevents critically perfused tissue from ischemic necrosis. Tissue protection is the result of a nitric oxide synthase-mediated improvement of the microcirculation but not due to induction of angiogenesis or attenuation of inflammation. This might represent a promising, noninvasive, and clinically applicable approach to protect musculocutaneous tissue from ischemia.

Metabolomic linkage reveals functional interaction between glucose-dependent insulinotropic polypeptide and ghrelin in humans

The gastric peptide ghrelin promotes energy storage, appetite, and food intake. Nutrient intake strongly suppresses circulating ghrelin via molecular mechanisms possibly involving insulin and gastrointestinal hormones. On the basis of the growing evidence that glucose-dependent insulinotropic polypeptide (GIP) is involved in the control of fuel metabolism, we hypothesized that GIP and/or insulin, directly or via changes in plasma metabolites, might affect circulating ghrelin. Fourteen obese subjects were infused with GIP (2.0 pmol·kg(-1)·min(-1)) or placebo in the fasting state during either euglycemic hyperinsulinemic (EC) or hyperglycemic hyperinsulinemic clamps (HC). Apart from analysis of plasma ghrelin and insulin levels, GC-TOF/MS analysis was applied to create a hormone-metabolite network for each experiment. The GIP and insulin effects on circulating ghrelin were analyzed within the framework of those networks. In the HC, ghrelin levels decreased in the absence (19.2% vs. baseline, P = 0.028) as well as in the presence of GIP (33.8%, P = 0.018). Ghrelin levels were significantly lower during HC with GIP than with placebo, despite insulin levels not differing significantly. In the GIP network combining data on GIP-infusion, EC+GIP and HC+GIP experiments, ghrelin was integrated into hormone-metabolite networks through a connection to a group of long-chain fatty acids. In contrast, ghrelin was excluded from the network of experiments without GIP. GIP decreased circulating ghrelin and might have affected the ghrelin system via modification of long-chain fatty acid pools. These observations were independent of insulin and offer potential mechanistic underpinnings for the involvement of GIP in systemic control of energy metabolism.

Acylated and des acyl ghrelin in human portal and systemic circulations

Octanoylation of the gastric peptide ghrelin produces an active isoform that regulates appetite and other metabolic functions. Acylated ghrelin is present in the gastrointestinal tract suggesting that octanoylation may occur in these tissues and thereby affect the acylated ghrelin in the systemic circulation. In this study blood samples were collected simultaneously from portal, arterial, peripheral venous and central venous compartments from patients undergoing laparotomy. ELISA and high sensitivity Bioplex was used to measure the concentration of acylated and des acyl ghrelin. We found median (95% confidence interval (CI)) plasma acylated ghrelin (pg/ml) was 35.8 (30.0-59.6) in the portal compartment compared to 51.5 (37.6-74.8; P < 0.05, n = 11) in the arterial, 39.3 (33.3-56.3) in the portal compartment compared to 55.0 (48.5-77.0; P < 0.001, n = 12) in the peripheral venous and 36.0 (33.1-57.4) in the portal compartment compared to 48.9 (43.3-65.6; P < 0.01, n = 15) in the central venous compartment. Median (95% CI) plasma des acyl ghrelin levels (pg/ml) was 173 (125-220) in the portal compartment compared to 136 (99.3-125; P < 0.001, n = 14)in the arterial, 186 (136-233) in the portal compartment compared to 149 (111-190; P < 0.01, n = 15) in the peripheral venous and 171 (140-208) in the portal compartment compared to 152 (119-175; P < 0.01, n = 15) the central venous compartment. We conclude that plasma acylated ghrelin concentration was significantly lower in portal compared with the systemic compartments whilst plasma des acyl ghrelin was significantly higher in portal compared with systemic compartments. These findings suggest that the liver could be involved in the regulation of circulating ghrelin.

A rat model of childhood diet-induced obesity: Roux-en-Y gastric bypass induced changes in metabolic parameters and gastric peptide ghrelin

Childhood morbid obesity is reaching epidemic proportions. Roux-en-Y gastric bypass (RYGB) results in many metabolic alterations, including changes in glucose and lipid metabolism, and changes in levels of the gastric hormone, ghrelin. As more children are undergoing RYGB, an animal model would be beneficial to further study RYGB and its subsequent metabolic effects. DIO Sprague Dawley rats underwent RYGB, sham jejunojejunostomy (SH), or no operation (HFC) after 6 weeks of high-fat diet. Non-obese rats fed standard chow (SC) were a final control group. Animals were post-operatively fed standard chow for 7 days before sacrifice. At sacrifice, venous blood and gastric mucosa was collected for metabolic parameters and ghrelin determination. RYGB rats weighed less than SH and HFC (361 +/- 8.8 vs. 437 +/- 9.3 and 443 +/- 6.2 g, P < 0.05). Compared to HFC, RYGB animals had decreased plasma glucose (292 +/- 23 vs. 141 +/- 10 mg/dL), cholesterol (80 +/- 12 vs. 45 +/- 5 mg/dL), triglycerides (138 +/- 37 vs. 52 +/- 7 mg/dL), HDL (43 +/- 5 vs. 20 +/- 3 mg/dL), and free fatty acids (0.72 +/- 0.14 vs. 0.23 +/- 0.02 mEq/L), all P < 0.05. Plasma ghrelin increased in RYGB rats compared to SC and HFC (116.22 +/- 32.27 vs. 31.60 +/- 2.66 and 31.75 +/- 0.75 pg/mL, P < 0.05). In a rat model of RYGB, we demonstrated improved metabolic parameters and increased plasma and gastric mRNA ghrelin levels. The rat model for RYBG appears to be a reasonable model for future study of the cellular and molecular regulatory pathways of obesity and its surgical treatment.

Early Changes in Ghrelin following Roux-en-Y Gastric Bypass: Influence of Vagal Nerve Functionality?

Roux-en-Y gastric bypass (RYGBP) effectively produces massive weight reduction, improving health in morbidly obese patients. The mechanisms for the weight loss, and the fate of the excluded gastric mucosa, are not fully clarified. To what extent the appetite-stimulating gastric peptide ghrelin is affected remains controversial. Circulating concentrations of ghrelin, pancreatic polypeptide (PP), pepsinogen I (PGI) and gastrin were examined in 15 morbidly obese patients (median BMI 45 kg/m2) preoperatively, and on days 1, 2, 4, 6 and at months 1, 6 and 12 after RYGBP. Ghrelin levels fell on postoperative day 1 and increased after 1 month to preoperative levels, and rose further at 6 and 12 months. PP concentrations decreased on day 1 and subsequently returned to preoperative levels. PGI levels peaked transiently the first days after surgery and subsequently declined to lower than preoperative levels. Gastrin levels were gradually reduced postoperatively. Ghrelin and PP fall transiently after surgery, possibly due to vagal dysfunction, and ultimately, as weight loss ensues, ghrelin secretion increases to higher than preoperative levels. The RYBGP procedure affects the gastric mucosa, as reflected by a transient increase in circulating PGI, and subsequently, the mucosa in the excluded stomach is at rest, as shown by low levels of PGI and gastrin.

A comparison of oral and transdermal short-term estrogen therapy in postmenopausal women with metabolic syndrome

To determine whether it would be preferable to prescribe oral or transdermal estrogen to symptomatic postmenopausal women with metabolic syndrome (MBS). Prospective, randomized study. Academic medical center. Fifty obese postmenopausal women with MBS. Women were randomized to receive either oral E(2) (oE(2), 1 mg/d) or transdermal E(2) (tE(2), 0.05 mg/d) for 3 months. Fasting blood was obtained before and after treatment for glucose, insulin, lipid profiles, the adipocytokines (adiponectin, leptin, and resistin), and a gastric peptide (ghrelin). In addition, a 75-g 2-hour oral glucose-tolerance and intravenous insulin-tolerance tests were performed before and after E(2). Changes in parameters of insulin resistance (IR), lipid profiles, and adipocytokine levels. Mean serum concentrations of E(2) in women using oE(2) and tE(2) were 39.1 +/- 5.6 and 49.2 +/- 28.6 pg/mL, respectively. After oE(2), there was a statistically significant worsening of IR markers, including an increase in baseline insulin (15.28 +/- 1.27 to 22.02 +/- 2.40 microU/mL), a reduction in quantitative insulin-sensitivity check index (0.3177 +/- 0.0043 to 0.2977 +/- 0.0057), and an increase in homeostasis model assessment (3.96 +/- 0.38 to 8.59 +/- 2.08). The only significant change in the lipid profile was an increase in high-density-lipoprotein cholesterol (50.46 +/- 2.34 vs. 55.08 +/- 2.51 mg/dL). Leptin levels increased (81.43 +/- 7.87 ng/mL to 94.10 +/- 6.56 ng/mL), and adiponectin decreased nonsignificantly, resulting in an increased leptin-adiponectin ratio (12.56 +/- 1.70 to 15.86 +/- 2.24); resistin levels increased (9.37 +/- 1.09 ng/mL to 11.72 +/- 1.10 ng/mL); and baseline ghrelin levels decreased (701.64 +/- 59.79 pg/mL to 581.72 +/- 36.07 pg/mL). After tE(2), no significant changes in IR parameters occurred, except for a decrease in glucose-insulin ratio. There were no changes in lipid parameters. Leptin did not change (72.7 +/- 9.3 ng/mL to 78.8 +/- 7.9 ng/mL), whereas adiponectin levels showed statistically significant increase (7.97 +/- 0.7 microg/mL vs. 9.96 +/- 1.1 microg/mL), with no change in the leptin-adiponectin ratio. Resistin levels did not change significantly, and ghrelin levels decreased (888.52 +/- 109.98 pg/mL vs. 579.04 +/- 39.30 pg/mL). This short-term study suggests that oral E(2) may worsen IR and adipocytokine parameters, worsening cardiovascular risk. Transdermal E(2) had minimal effects on IR and resulted in higher adiponectin. Although these data may not reflect alterations that occur with estrogen therapy in more metabolically normal postmenopausal women or with longer term therapy, the findings suggest that tE(2) may be a preferable treatment for obese women with MBS. Long-term studies are needed to make any recommendations.

Increase in adiponectin levels during pioglitazone therapy in relation to glucose control, insulin resistance as well as ghrelin and resistin levels

Glitazones increase the secretion of the adipocyte-derived hormone adiponectin. Furthermore, the gastric signal peptide ghrelin is known to suppress adiponectin expression in adipocyte cell culture models. It is not known whether the increase in adiponectin during glitazone therapy is due to a suppression of ghrelin levels, a decrease of resistin concentrations or an amelioration of glucose control. In 10 patients (age 71+/-9 yr, body mass index 29.9+/-3.6 kg/m(2), HbA1c 6.9+/-0.5%) with Type 2 diabetes, who had already been treated with sulfonylureas, we additionally initiated a pioglitazone therapy (30 mg/day) for 12 weeks. To investigate the pioglitazone effect independently of blood glucose, glycosylated hemoglobin (HbA1c) was kept unchanged by reducing the daily dose of sulfonylurea if necessary. Ghrelin concentration [radioimmunoassay (RIA), Phoenix Pharmaceuticals, Mountain View, CA, USA], adiponectin levels [enzyme-linked immunosorbent assay (ELISA), Biovendor, Heidelberg, Germany] as well as resistin concentrations (ELISA, Linco Research, St. Charles, MO, USA) were measured before and after pioglitazone. Glucose control remained unchanged within the 12-week pioglitazone therapy (HbA1c 6.9+/-0.5% before vs 6.8+/-0.6% after pioglitazone) while body weight increased from 86.6+/-9.2 to 88.0+/-9.4 kg (p<0.05), and insulin concentration decreased from 19.6+/-5.7 to 10.1+/-1.6 microU/ml (p<0.05). Adiponectin concentration increased in all patients from 7.70+/-2.47 to 23.33+/-8.28 microg/ml (p<0.01), while resistin concentrations tended to decrease (by 15%; p=0.059). However, ghrelin remained unchanged during therapy. No correlations were observed either between ghrelin, resistin, insulin and adiponectin, or between body weight and hormone plasma levels. The increase in adiponectin levels during pioglitazone therapy seems to be at least partly independent of blood glucose and insulin concentration as well as of ghrelin levels, and it was not associated with a decrease in resistin concentrations.

The gastric peptide ghrelin increases gastric emptying in patients with diabetic gastroparesis,

The gastric peptide ghrelin increases gastric emptying in patients with diabetic gastroparesis,

Ghrelin receptors in rat and human nodose ganglia: putative role in regulating CB-1 and MCH receptor abundance

Intact vagal afferent neurons are required for the satiety effects of the intestinal hormone cholecystokinin (CCK) and the orexigenic effects of the gastric regulatory peptide ghrelin. In this study, we examined the localization of ghrelin receptors in nodose ganglia and their function in regulating the expression of other orexigenic receptors, notably cannabinoid (CB)-1 and melanin-concentrating hormone (MCH)-1 receptors. With the use of RT-PCR, transcripts corresponding to both functional [growth hormone secretagogue receptor (GHS-R)1a] and truncated forms (GHS-R1b) of the ghrelin receptor were detected in rat nodose ganglia. There was no difference in expression between rats fed ad libitum or fasted for up to 48 h. Immunohistochemical studies using antibodies directed at GHS-R1a revealed expression in over 75% of neurons also expressing CCK-1 receptors in the mid- and caudal regions of the ganglion. There was also expression in human nodose ganglia. In fasted rats in which CB-1 and MCH-1 receptor expression was increased, administration of ghrelin prevented the downregulation by refeeding. We conclude that the actions of CCK and ghrelin are mediated by a common population of vagal afferent neurons. Ghrelin may act to limit the action of CCK in depressing expression of CB-1 and MCH-1 receptors and other receptors.

Insulin resistance in postmenopausal women with metabolic syndrome and the measurements of adiponectin, leptin, resistin, and ghrelin

Metabolic syndrome (MBS) is a significant health care problem in postmenopausal women and is driven largely by obesity. We wished to assess the prevalence of insulin resistance (IR), diagnosed using practical methods, and whether several adipocyte factors (adiponectin, leptin, resistin) or the gastric peptide ghrelin, associated with cardiovascular risk, might be abnormal and may relate to IR. We evaluated 37 obese postmenopausal women with MBS and 34 matched obese premenopausal controls, as well as 14 non-obese premenopausal controls. We measured fasting glucose and insulin, performed 75 g 2 hr oral glucose tolerance and intravenous insulin tolerance tests to assess IR, and measured fasting lipids, adiponectin, leptin, resistin and ghrelin. The kinetic decline in glucose after insulin (kITT) as a marker of IR was the most frequently abnormal test (abnormal in 81%), with QUICKI, HOMA, and a modification of the Matsuda-DeFronzo index (ISIM) abnormal in 76, 73, and 68%, respectively. The GIR was abnormal in only 35% of subjects. Leptin and resistin were elevated and adiponectin and ghrelin were decreased in the postmenopausal women, compared to both groups of premenopausal controls. BMI correlated strongly with markers of insulin resistance as well as adipocytokine values. After controlling for BMI, only leptin was predictive of ISIM. Being overweight after menopause results in worsening IR and elevations in adipocytokine levels. While BMI is the most important factor, abnormal adipocytokine secretion may enhance IR and increase cardiovascular risk in postmenopausal women.

Insulin, unlike food intake, does not suppress ghrelin in human subjects.

Food intake suppresses plasma levels of the gastric peptide ghrelin in humans. We hypothesize that the food intake- suppression of ghrelin could be secondary to the plasma glucose and insulin changes after a meal. The aim of this study was to compare the effect of the administration of a combined pulse of glucose and insulin to the effect of one meal on plasma ghrelin in human subjects. A secondary aim was to study the effect of an oral glucose load on ghrelin levels. Experiment 1 (n = 10) studied plasma glucose, insulin, leptin and ghrelin for 6 hours after a 790 kcal liquid meal. In Experiment 2 (n = 7), a subcutaneous pulse of insulin (Humalog 0.03U/kg) and an I.V. infusion of glucose were administered in order to mimic the plasma changes of glucose and insulin after a meal, and plasma ghrelin levels were monitored for 9 h. The OGTT data was used to study the effect of oral glucose on ghrelin. A mixed liquid meal decreased basal serum ghrelin by 26% at 40 minutes (p = 0.009). A 75 gr oral glucose load suppresses ghrelin by 28% at 30 minutes. Contrary to the meal effect, the parenteral administration of insulin and glucose did not suppress serum ghrelin. Unlike food intake, the administration of insulin and glucose does not suppress ghrelin levels. These data suggest that the suppressive effect of food intake or oral glucose on serum ghrelin is unlikely mediated by the changes of plasma insulin and glucose observed after the ingestion.

Ghrelin is an appetite-stimulatory signal from stomach with structural resemblance to motilin

Background & Aims: Ghrelin, an endogenous ligand for growth hormone secretagogue receptor, was recently identified in the rat stomach. We examined the effects of the gastric peptide ghrelin on energy balance in association with leptin and vagal nerve activity. Methods: Food intake, oxygen consumption, gastric emptying, and hypothalamic neuropeptide Y (NPY) messenger RNA expression were measured after intra-third cerebroventricular or intraperitoneal injections of ghrelin in mice. The gastric vagal nerve activity was recorded after intravenous administration in rats. Gastric ghrelin gene expression was assessed by Northern blot analysis. Repeated coadministration of ghrelin and interleukin (IL)-1β was continued for 5 days. Results: Ghrelin exhibited gastroprokinetic activity with structural resemblance to motilin and potent orexigenic activity through action on the hypothalamic neuropeptide Y (NPY) and Y1 receptor, which was lost after vagotomy. Ghrelin decreased gastric vagal afferent discharge in contrast to other anorexigenic peptides that increased the activity. Ghrelin gene expression in the stomach was increased by fasting and in ob/ob mice, and was decreased by administration of leptin and IL-1β. Peripherally administered ghrelin blocked IL-1β–induced anorexia and produced positive energy balance by promoting food intake and decreasing energy expenditure. Conclusions: Ghrelin, which is negatively regulated by leptin and IL-1β, is secreted by the stomach and increases arcuate NPY expression, which in turn acts through Y1 receptors to increase food intake and decrease energy expenditure. Gastric peptide ghrelin may thus function as part of the orexigenic pathway downstream from leptin and is a potential therapeutic target not only for obesity but also for anorexia and cachexia.GASTROENTEROLOGY 2001;120:337-345