Injection Of Ghrelin Research Articles

Obestatin partially suppresses ghrelin stimulation of appetite in “high-responders” grass carp, Ctenopharyngodon idellus

Ghrelin and obestatin are two gastrointestinal peptides obtained by post-translational processing of a common precursor, preproghrelin. The effect of obestatin on food intake is still controversial. The aim of the present study was to investigate the effects of ghrelin and obestatin on food intake in grass carp, Ctenopharyngodon idellus. Fish received intraperitoneal (IP) injection of saline, ghrelin (100ngg−1BW), obestatin-like (25ngg−1BW) and ghrelin in combination with obestatin-like. Ghrelin stimulation of food intake varied considerably among individual fish with 70.8% eliciting a robust response. In these high-responders, food intake was significantly increased by IP ghrelin within 2h. Co-administration of ghrelin and obestatin-like resulted in a decrease in food intake, indicating that obestatin was able to antagonize the effect of ghrelin. However, IP obestatin-like alone could not regulate food intake in grass carp. RT-PCR analysis demonstrated that IP ghrelin peptide led to a significant increase in mRNA abundance of NPY, Y8a and Y8b genes compared to saline injected fish, while in combination with obestatin-like peptide decreased ghrelin-induced gene expressions of these three genes. IP sole obestatin-like peptide did not modify the expression levels of NPY, Y8a, Y8b, CART and POMC compared to the control group. Therefore, IP administration of obestatin-like peptide, partially blocking the ghrelin-induced appetite, investigated the possible involvement of obestatin as a mediator of the ghrelin stimulatory action on food intake, at least in “high-responders” grass carp.

Ghrelin ameliorates intestinal barrier dysfunction in experimental colitis by inhibiting the activation of nuclear factor-kappa B

AimThis study aimed to investigate the effect and underlying mechanism of ghrelin on intestinal barrier dysfunction in dextran sulfate sodium (DSS)-induced colitis. Methods and resultsAcute colitis was induced in C57BL/6J mice by administering 2.5% DSS. Saline or 25, 125, 250 μg/kg ghrelin was administrated intraperitoneally (IP) to mice 1 day before colitis induction and on days 4, 5, and 6 after DSS administration. IP injection of a ghrelin receptor antagonist, [D-lys3]-GHRP-6, was performed immediately prior to ghrelin injection. Ghrelin (125 or 250 μg/kg) could reduce the disease activity index, histological score, and myeloperoxidase activities in experimental colitis, and also prevented shortening of the colon. Ghrelin could prevent the reduction of transepithelial electrical resistance and tight junction expression, and bolstered tight junction structural integrity and regulated cytokine secretion. Ultimately, ghrelin inhibited nuclear factor kappa B (NF-κB), inhibitory κB-α, myosin light chain kinase, and phosphorylated myosin light chain 2 activation. ConclusionsGhrelin prevented the breakdown of intestinal barrier function in DSS-induced colitis. The protective effects of ghrelin on intestinal barrier function were mediated by its receptor GHSR-1a. The inhibition of NF-κB activation might be part of the mechanism underlying the effects of ghrelin that protect against barrier dysfunction.

The effect of ghrelin and estradiol on mean concentration of thyroid hormones.

Background:Ghrelin is a novel peptide hormone that has GH releasing activity and also other endocrine and metabolic functions. It can also increase food intake and decrease T3 and T4 concentrations. Several parameters of hypothalamic-pituitary-thyroid (HPT) axis function are modulated by 17β-estradiol (E2).Objectives:The purpose of this study was to investigate the effect of interactions between ghrelin and estradiol (injected via ICV route) on plasma T3 and T4 concentrations in female rats.Materials and Methods:Eighteen Wistar female rats (bodyweight, 200-250 g) were randomly divided into three groups. Group 1 received estradiol, Group 2 received ghrelin and Group 3 received ghrelin and estradiol. Plasma samples were used to assess T3 and T4 concentration by RIA.Results:The results indicated that ghrelin significantly decreased thyroid hormone concentrations, whereas estradiol increased these concentrations. The simultaneous injection of ghrelin and estradiol significantly decreased the inhibitory effect of ghrelin on thyroid hormone concentrations (P < 0.05).Conclusions:According to the results of this study, both ghrelin and estradiol affect the concentration of thyroid hormone but in opposite directions. This difference might be due to different underlying hormonal mechanisms such as HPA and/or HPT axis melanocyte stimulating hormone (MSH) systems could be suggested.

Ghrelin effects on midgut tissue antioxidative defense and glutathioneS-transferase activity in Lymantria dispar (Lepidoptera)

The aim of the study was to examine changes in Cu?Zn superoxide dismutase (SOD), catalase (CAT), their gel electrophoresis profiles, glutathione reductase (GR) activity, amount of glutathione (GSH), and the activity of glutathione S-transferase (GST) - phase II biotransformation enzyme in the midgut tissue of gypsy moth (Lymantria dispar L. (Lepidoptera: Lymantriidae)) larvae after ghrelin treatment. Four subpicomolar injections of ghrelin (0.3 pmol) or physiological saline (control) were applied every 24 h. The SOD, CAT, GR, GST activity, and amount of GSH were higher in the ghrelin-treated group than in the control. Electrophoresis gel bands of SOD and CAT had higher area and density in the treated group. The effects of ghrelin on the antioxidative defense and GST activity in insects were detected for the first time. The results provided evidence for possible application of insects as simple model systems in future studies of the role of ghrelin in the antioxidative protection of complex organisms.

Characterization of ghrelin-sensitive neurons in the lumbosacral defecation center in rats.

Ghrelin is involved in the regulation of somatic growth, feeding behavior and energy homeostasis. Ghrelin stimulates neuropeptide Y (NPY) neurons and activates intracellular AMP-activated protein kinase (AMPK) in the hypothalamus. These NPY neurons also express the leptin receptor and leptin inhibits ghrelin-induced activation of NPY neurons. In the spinal cord, we have demonstrated colokinetic action of ghrelin. However, the precise characteristics of the ghrelin-sensitive neurons remain to be clarified. The aim of this study was firstly to confirm that the action of ghrelin is mediated via a neurogenic pathway in the spinal cord, and secondly to characterize the ghrelin-sensitive neurons by comparing with hypothalamic ghrelin-sensitive neurons. Rats were anesthetised with alpha-chloralose and ketamine, and colorectal intraluminal pressure and expelled volume were recorded in vivo. Drugs were applied intrathecally. Ghrelin caused enhancement of propulsive contractions. Tetrodotoxin completely blocked the colokinetic effect of ghrelin. An AMPK activator, aminoimidazole carboxamide ribonucleotide, failed to mimic the ghrelin effect. Leptin had no effect on the spontaneous contractions and did not exert a suppressive effect on the ghrelin-enhanced colorectal motility. An NPY Y1 receptor antagonist did not affect the action of ghrelin. NPY had no effect on the colorectal motility. This study showed that intrathecal injection of ghrelin stimulates colorectal motility by acting on ghrelin-sensitive neurons in the lumbosacral defecation center. The characteristics of ghrelin-sensitive neurons in the spinal cord are quite different from those of ghrelin-sensitive neurons in the hypothalamus.

Ghrelin Is a Novel Regulator of GLP-1 Secretion.

GLP-1 is a gastrointestinal L-cell hormone that enhances glucose-stimulated insulin secretion. Hence, strategies that prevent GLP-1 degradation or activate the GLP-1 receptor are used to treat patients with type 2 diabetes. GLP-1 secretion occurs after a meal and is partly regulated by other circulating hormones. Ghrelin is a stomach-derived hormone that plays a key role in whole-body energy metabolism. Because ghrelin levels peak immediately before mealtimes, we hypothesized that ghrelin plays a role in priming the intestinal L-cell for nutrient-induced GLP-1 release. The intraperitoneal injection of ghrelin into mice 15 min before the administration of oral glucose enhanced glucose-stimulated GLP-1 release and improved glucose tolerance, whereas the ghrelin receptor antagonist D-Lys GHRP-6 reduced plasma levels of GLP-1 and insulin and diminished oral glucose tolerance. The ghrelin-mediated improvement in glucose tolerance was lost in mice coinjected with a GLP-1 receptor antagonist as well as in Glp1r(-/-) mice lacking the GLP-1 receptor. The impaired oral glucose tolerance in diet-induced obese mice was also improved by ghrelin preadministration. Importantly, ghrelin directly stimulated GLP-1 release from L-cell lines (murine GLUTag, human NCI-H716) through an extracellular signal-related kinase 1/2-dependent pathway. These studies demonstrate a novel role for ghrelin in enhancing the GLP-1 secretory response to ingested nutrients.

Ghrelin’s effects in diabetic retinopathy: Inhibition of choroid retinal cells migration cultured under a hyperglycemic environment.

AbstractPurpose The purpose of this work is to investigate the effect of ghrelin in a primate choroid retinal cell line cultured under hyperglycemic conditions and its effect on the early changes of diabetic retinopathy in an animal model of type1 diabetes mellitus (DM1).Methods A RF/6a cell line was used in the in vitro assay. Cell migration was assessed using the wound healing assay under increasing (0‐300mM) glucose concentrations. To test its effect, ghrelin was added (10‐5‐10‐10nM) to the cell cultures for 24h. Positive controls had VEGF added to the medium. For the in vivo studies, diabetic Wistar rats received intravitreal injections of either ghrelin (81nM) or saline every 4 weeks for 3 months. Vascular permeability was assessed using the Evans blue assay.Results Increasing concentrations of glucose show a reduction in cell migration distance. We defined 10 mM of glucose as the basal and 250 mM as the hyperglycemic condition. At a concentration of 10‐8 nM ghrelin potentiates the reduction of migration induced by the hyperglycemic medium, and reduces the migration induced by VEGF. Regarding the in vivo model, diabetic animals treated with intravitreal ghrelin injections showed no alteration in vascular permeability, when compared with diabetic controls.Conclusion Ghrelin reduces cell migration in choroid‐retinal cells under hyperglycemic media, but appears to have no effect on the vascular permeability in a DM1 animal model.

Ghrelin increases lymphocytes in chronic normobaric hypoxia.

Hypoxia is a condition of decreased availability of oxygen. To adapt hypoxia, some changes in blood cells occur in the body. The aim of this study was to evaluate the effect of ghrelin on different types of blood cell in normobaric hypoxia situation. Thirty-two animals were divided in 4 groups (n=8): control (C), ghrelin (G), hypoxia (H), and hypoxic animals that received ghrelin (H+G). Hypoxia (11%) was induced by an Environmental Chamber System GO2 Altitude. Animals in ghrelin groups received a subcutaneous injection of ghrelin (150 &mu;g/kg/day) for 14 days. Our results show that ghrelin significantly (p<0.05) increased RBC and Hct levels, whereas it significantly (p<0.05) decreased lymphocytes in the blood. RBC, Hct, Hb concentration, platelet and MCV increased significantly (p<0.05) in hypoxic conditions but lymphocytes, monocytes and Polymorphonuclears did not show any significant changes. Platelets had a significant (p<0.05) decrease in hypoxic conditions and ghrelin administration in hypoxic conditions could increase lymphocyte levels significantly (p<0.05). Effect of ghrelin on blood cells could be related to blood oxygen level. Ghrelin in normal oxygen conditions increases RBC and Hct levels but decreases lymphocytes, whereas in hypoxic conditions, ghrelin increases blood lymphocytes.

Ghrelin-induced hypophagia is mediated by the β2 adrenergic receptor in chicken.

The purpose of this study was to examine the effects of intracerebroventricular injection of metoprolol (a β1 adrenergic receptor antagonist), ICI 118,551 (a β2 adrenergic receptor antagonist), and SR 59230R (a β3 adrenergic receptor antagonist) on ghrelin-induced food and water intake by 3-h food-deprived (FD3) cockerels. The chickens were randomly allocated to 4 treatment groups with 8 replicates in each group. A cannula was surgically implanted into the lateral ventricle of the brain. In experiment 1, chickens received the β1 adrenergic receptor antagonist (24 nmol) before injection of the ghrelin (0.6 nmol). In experiment 2, chickens received the β2 adrenergic receptor antagonist (5 nmol) before injection of the ghrelin (0.6 nmol). In experiment 3, birds were injected with ghrelin (0.6 nmol) after the β3 adrenergic receptor antagonist (20 nmol). Cumulative food and water intake were recorded 3-h post injection and analyzed by two-way analysis of variance. According to the results, ghrelin injection reduced food and water intake by broiler cockerels (p≤0.05). The effect of ghrelin on food intake was significantly attenuated by pretreatment with the β2 receptor antagonist (p≤0.05). Furthermore, the β2 receptor antagonist had no effect on water intake induced by ghrelin. Also, pretreatment with the β1 and β3 receptors antagonists had no effect on ghrelin-induced food and water intake. These results suggest that the effect of ghrelin on cumulative food intake by cockerels is mediated via β2 adrenergic receptors.

The Antiepileptic Effect of Ghrelin During Different Phases of the Estrous Cycle in PTZ-Induced Seizures in Rat

Catamenial epilepsy is a special form of epilepsy in women whom seizure aggravation is arranged with menstrual cycle that may affect up to 70 % of epileptic women. Antiepileptic effect of Ghrelin hormone has been proved recently. Due to effects of Ghrelin on GABA and LH concentration and periodic variation in the level of estrogen (E2) and progesterone (P4) during menstrual cycle, it seems that antiepileptic effect of Ghrelin can be different during various phases of estrous cycle. So this study was conducted to survey antiepileptic effect of Ghrelin during various phases of estrous cycle in rats. 72 adult female Wistar rats in three groups (control, 40 and 80 μg/kg of Ghrelin), each with four subgroups (proestrus, estrus, metestrus and diestrus) were used (n = 6). Then, intracerebroventricular (ICV) injection of Ghrelin (40 and 80 μg/kg) followed by intraperitoneal injection of 80 μg/kg pentylenetetrazole in control and treatment groups were done. Initiation time of myoclonic seizures (ITMS), initiation time of tonic–clonic seizures (ITTS), seizures duration and mortality rate were monitored and recorded for 30 min. Results showed that, ICV injection of Ghrelin significantly increased ITMS and ITTS during luteal phase than follicular phase compared to control group (P < 0.05). Also, seizure duration significantly decreased after ICV injection of Ghrelin during luteal phase and follicular phase compared to control group (P < 0.05). Furthermore, there was no mortality after ICV injection of Ghrelin (40 and 80 μg/kg) during luteal and follicular phases compared to control group (P < 0.05). These results suggest that Ghrelin has antiepileptic effects which are more prominent during luteal phase than follicular phase.

Cyclic estradiol treatment modulates the orexigenic effects of ghrelin in ovariectomized rats

Data from a wide variety of mammalian species indicate that feeding behavior can be influenced by changes in endogenous estrogens and exogenous estrogenic treatments. Ghrelin is an important physiological signal for the regulation of energy balance, and ghrelin treatment increases eating and body weight in male rodents. The following studies evaluated the hypothesis that the inhibitory effects of estradiol on feeding involve interactions with orexigenic peptides by examining the ability of estradiol to modulate the behavioral effects of ghrelin in female rats. In these experiments, adult rats were ovariectomized and assigned to an estradiol benzoate (EB) or an oil (control) group. Three weeks after ovariectomy, animals received two daily subcutaneous injections of EB or the oil vehicle. Animals then received intraperitoneal (ip) injections of ghrelin (6.0 or 12.0nmol) or saline during the nocturnal and diurnal periods three days after the first injection of estradiol or oil. Food intake, meal size, and meal number were determined during the 2-hour period following ghrelin or saline treatments. Ghrelin significantly increased food intake during nocturnal tests in oil-treated but not estradiol-treated rats. The hyperphagic effects of ghrelin on nocturnal food intake were also accompanied by an increase in meal size, and this effect of ghrelin on meal size was attenuated in estradiol-treated females. These findings support the hypothesis that the effects of estradiol on feeding behavior involve an attenuation of orexigenic signals, possibly by modulating the effects of the peripheral ghrelin signal on hypothalamic neuropeptides involved in the control of food intake.

Ghrelin Protects Rats Against Traumatic Brain Injury and Hemorrhagic Shock Through Upregulation of UCP2

To determine the mechanism responsible for ghrelin's neuroprotective effects after traumatic brain injury (TBI) and hemorrhagic shock. Ghrelin, a gastrointestinal hormone, has been demonstrated to possess multiple functions, including upregulation of uncoupling protein 2 (UCP2) and stimulation of the vagus nerve. Recent evidence has indicated that ghrelin is neuroprotective. We, therefore, hypothesized that ghrelin protects rats against TBI and hemorrhagic shock through upregulation of UCP2, involving stimulation of the vagus nerve. Brain injury was induced by dropping a 450 g of weight from 1.5 m onto a steel helmet attached to the skull of male adult rats. Immediately after TBI, a midline laparotomy was performed, and both lumbar veins were isolated and severed at the junction with the vena cava. The abdomen was kept open for 20 minutes. At 45 minutes after TBI and uncontrolled hemorrhage (UH), ghrelin (4, 8, or 16 nmol/rat) or 1 mL of normal saline (vehicle) was intravenously administered. The Neurological Severity Scale (NSS), morphological alterations and β-amyloid precursor protein expression in the brain, systemic organ injury markers (ie, alanine aminotransferase, aspartate aminotransferase, and lactate), and UCP2 expression in the cortex were measured. To determine whether the protective effect of ghrelin is mediated through upregulation of UCP2, genipin, a specific UCP2 antagonist, was administered intravenously before the injection of ghrelin in animals with TBI and UH. The role of the vagus nerve was assessed by performing vagotomy immediately before ghrelin administration. Ghrelin attenuated brain injury and facilitated functional recovery after TBI and UH. Ghrelin increased UCP2 expression in the cortex, and administration of genipin abolished ghrelin's protection after TBI and UH. Furthermore, vagotomy prevented the beneficial effects of ghrelin and eliminated ghrelin-induced UCP2 upregulation after TBI and UH. The protective effects of ghrelin after TBI and UH seem to be related to upregulation of UCP2 expression in the brain and requiring the intact vagus nerve.

Ghrelin alters the stimulatory effect of cocaine on ethanol intake following mesolimbic or systemic administration

Emerging evidence suggests that ghrelinergic and dopaminergic signaling interact in the neural control of motivation and ethanol reward. To further investigate a possible interaction between these two neurochemical systems, we examined the impact of ghrelin, cocaine and combined injections of ghrelin with cocaine, on voluntary ethanol intake. Male Sprague–Dawley rats were habituated to an 8% ethanol solution until intakes stabilized. Rats were then injected with ghrelin (2.5–10 nmol IP), cocaine (0.625–10 mg/kg IP) or ghrelin paired with cocaine. We also examined the impact of direct ghrelin (30–300 pmol) injections into the ventral tegmental area (VTA) co-administered with systemic cocaine. Ethanol consumption was measured at 2 and 6 h postinjection. While ghrelin and cocaine reliably increased ethanol intake, peripheral administration of the peptide elicited a dose-dependent differential effect on cocaine-induced intake. Pretreatment with ghrelin potentiated the effect of cocaine on ethanol intake at a low dose of 2.5 nmol, whereas 10 nmol suppressed cocaine-induced ethanol intake. This same 10 nmol dose was found to induce anxiogenic behavior as measured using an elevated plus maze paradigm. Finally, when injected directly into the VTA, ghrelin (300 pmol) potentiated the effect of systemic cocaine on ethanol intake. Combined subthreshold dosing of VTA ghrelin with a subthreshold dose of cocaine also evoked reliable increases in intake compared to vehicle. Overall, our data suggest that low doses of ghrelin elicit a stimulatory effect on cocaine-induced ethanol consummatory behavior and provide further support for an interactive role of dopaminergic and ghrelinergic transmission in ethanol reward.

Induced Ablation of Ghrelin Cells in Adult Mice Does Not Decrease Food Intake, Body Weight, or Response to High-Fat Diet

Injection of the peptide hormone ghrelin stimulates food intake in mice and humans. However, mice born without ghrelin demonstrate no significant loss of appetite. This paradox suggests either that compensation develops in mice born without ghrelin or that ghrelin is not essential for appetite control. To distinguish these possibilities, we generated transgenic mice (Ghrl-DTR) that express the diphtheria toxin receptor in ghrelin-secreting cells. Injection of diphtheria toxin in adulthood ablated ghrelin cells and reduced plasma ghrelin by 80%-95%. Ghrelin cell-ablated mice exhibited no loss of appetite or body weight and no resistance to a high-fat diet. To stimulate food intake in mice by ghrelin injection, we had to raise plasma levels many-fold above normal. Like germline ghrelin-deficient mice, the ghrelin cell-ablated mice developed profound hypoglycemia when subjected to prolonged calorie restriction, confirming that ghrelin acts to maintain blood glucose under famine conditions.

Ghrelin suppresses cardiac sympathetic tone following acute myocardial infarct ő mechanistic insight (1169.5)

Acute myocardial infarction (MI) initiates an increase in cardiac sympathetic nerve activity (SNA), which exacerbates ventricular remodelling and cardiac dysfunction. Ghrelin, a growth hormone‐releasing peptide, is effective at preventing this adverse increase in SNA, although the underlying mechanisms remain unknown. In this study we aimed to determine whether ghrelin could directly inhibited sympathetic tone within the brain, following acute MI. Cardiac SNA was continuously recorded in urethane‐anaesthetized rats for three hours following ligation of the left anterior descending coronary artery. Rats received an intracerebroventricular injection of either ghrelin (5 µg/kg) or placebo immediately after the MI. SNA remained stable in sham rats. Acute MI induced a maximal 420% increase in SNA, which was significantly attenuated, but not completely prevented, in those rats that received a central injection of ghrelin. These results suggest that ghrelin acts centrally within the brain to suppress SNA following acute MI. However, the fact that central ghrelin did not completely prevent the adverse increase in SNA, as previously reported for subcutaneous‐injected ghrelin, suggests that ghrelin may also act peripherally, e.g. cardiac vagal afferent fibers, to further prevent an increase in cardiac SNA following MI ‐ a hypothesis that warrants further investigation.

Crosstalking between the “gut-brain” hormone ghrelin and the circadian system in the goldfish. Effects on clock gene expression and food anticipatory activity

Ghrelin is a potent orexigenic signal mainly synthesized in the stomach and foregut of vertebrates. Recent studies in rodents point out that ghrelin could also act as an input for the circadian system and/or as an output of peripheral food-entrainable oscillators, being involved in the food anticipatory activity (FAA). In this study we pursue the possible interaction of ghrelin with the circadian system in a teleost, the goldfish (Carassius auratus). First, we analyzed if ghrelin is able to modulate the core clock functioning by regulating clock gene expression in fish under a light/dark cycle 12L:12D and fed at 10 am. As expected the acute intraperitoneal (IP) injection of goldfish ghrelin (gGRL[1–19], 44pmol/g bw) induced the expression of hypothalamic orexin. Moreover, ghrelin also induced (∼2-fold) some Per clock genes in hypothalamus and liver. This effect was partially counteracted in liver by the ghrelin antagonist ([D-Lys3]-GHRP-6, 100pmol/g bw). Second, we investigated if ghrelin is involved in daily FAA rhythms. With this aim locomotor activity was studied in response to IP injections (5–10days) of gGRL[1–19] and [D-Lys3]-GHRP-6 at the doses above indicated. Ghrelin and saline injected fish showed similar 24h activity patterns. However, ghrelin antagonist treatment abolished the FAA in schedule fed fish under 24h light, suggesting the involvement of the endogenous ghrelin system in this pre-feeding activity. Altogether these results suggest that ghrelin could be acting as an input for the entrainment of the food-entrainable oscillators in the circadian organization of goldfish.

Central injection of urocortin-3 but not corticotrophin-releasing hormone influences the ghrelin/GHS-R1a system of the proventriculus and brain in chicks

Ghrelin, the endogenous ligand for growth hormone secretagogue receptor 1a (GHS-R1a), stimulates food intake in mammals centrally and peripherally. In contrast, central injection of ghrelin inhibits feeding in neonatal chicks (Gallus gallus), which is thought to be mediated by the corticotrophin-releasing hormone (CRH) system, indicating that the mechanisms underlying ghrelin's action are different in chicks and mammals. However, the interaction between the ghrelin system and the CRH system has not been fully clarified in chicks. In the present study, we examined the effect of intracerebroventricular (ICV) injection of CRH and urocortin-3 (UCN-3), a CRH family peptide and an endogenous ligand for the CRH type-2 receptor (CRH-R2), on synthesis and secretion of ghrelin in chicks. Intracerebroventricular injection of UCN-3 but not CRH increased plasma ghrelin concentration (P < 0.05), diencephalic mRNA expression of ghrelin, and GHS-R1a (P < 0.05) and tended to decrease ghrelin (P = 0.08) and GHS-R1a (P = 0.10) mRNA expression in the proventriculus. Moreover, ICV injection of UCN-3 tended to increase diencephalic mRNA expression of CRH-R2 (P = 0.08) and CRH had no effect on it. In addition, ICV injection of CRH but not UCN-3 increased plasma corticosterone concentration (P < 0.05) and decreased the diencephalic mRNA expression of CRH-R1 (P < 0.05). These results clearly indicate that the roles of the CRH system for the ghrelin system are divided. The present study suggests that UCN-3 is mainly involved in the ghrelin system in chicks perhaps through the CRH-R2.

Effect of glucagon-like peptide-1 and ghrelin on liver metabolites in steers

Glucagon-like peptide 1 (GLP-1) and ghrelin have opposite regulatory effects on glucose metabolism in non-ruminants. However, mechanisms by which GLP-1 and ghrelin regulate nutrient partitioning, particularly in the liver, have been much less demonstrated in ruminants. A novel metabolomic method based on capillary electrophoresis time-of-flight mass spectrometry (CE-TOFMS) combined with multivariate statistical analysis was applied to address the GLP-1 and ghrelin-induced metabolic changes in the liver of steers. Three Holstein steers (400 ± 5.0 kg LW) fed a maintenance diet according to Japanese feeding standards were randomly assigned to three treatments (GLP-1, ghrelin and saline) in a 3 × 3 Latin square design with one week apart. Liver biopsies were taken 30 min after a single injection (1.0 μg/kg LW) of GLP-1 or ghrelin, and analysed for metabolites by Agilent CE-TOFMS system. Also, blood samples were collected for plasma hormones analysis. Results indicated that 20 and 10 liver metabolites were altered (P &lt; 0.05) by GLP-1 and ghrelin, respectively. Pathway analysis showed that GLP-1 is involved in biochemical pathways related to glycolysis/gluconeogenesis, lipogenesis and lipid export from the liver, oxidative stress defence and protein turnover. Ghrelin was shown to be involved in pathways related to glycolysis, protein anabolism and phospholipid biosynthesis. However, plasma concentrations of insulin, growth hormone and glucagon did not differ between treatments. These results imply that GLP-1 and ghrelin are involved in multibiochemical pathways that go beyond simply regulating glucose metabolism. In addition, the effects of GLP-1 and ghrelin may potentially be independent of insulin and growth hormone, respectively.

Organ-Specific Activation of the Gastric Branch of the Efferent Vagus Nerve by Ghrelin in Urethane-Anesthetized Rats

Ghrelin plays multiple physiological roles such as growth hormone secretion and exerting orexigenic actions; however, its physiological roles in the electrical activity of autonomic nerves remain unclear. Here, we investigated the effects of human ghrelin on several autonomic nerve activities in urethane-anesthetized rats using an electrophysiological method. Intravenous injection of ghrelin at 3 μg/kg significantly and transiently potentiated the efferent activity of the gastric vagus nerve; however, it did not affect the efferent activity of the hepatic vagus nerve. The activated response to ghrelin in the gastric efferent vagus nerve was not affected by the gastric afferent vagotomy, suggesting that this effect was not induced via the gastric afferent vagus nerve. Ghrelin did not affect the efferent activity of the brown adipose tissue, adrenal gland sympathetic nerve, and the renal sympathetic nerve. In addition, rectal temperature and the plasma concentrations of norepinephrine, corticosterone, and renin were also not changed by ghrelin. These findings demonstrate that ghrelin stimulates the gastric efferent vagus nerve in an organ-specific manner without affecting the gastric afferent vagus nerve and that ghrelin does not acutely affect the efferent basal activity of the sympathetic nerve in rats.

Ghrelin Alleviates Neuropathic Pain Through GHSR-1a–Mediated Suppression of the p38 MAPK/NF-κB Pathway in a Rat Chronic Constriction Injury Model

Neuropathic pain is related to the sustained activation of neuroglial cells and the production of proinflammatory cytokines in the spinal dorsal horn. Ghrelin, the endogenous ligand for growth hormone secretagogue receptor 1a (GHSR-1a), has been shown to inhibit the activation of microglia and the release of proinflammatory cytokines. The purpose of this study was to investigate the role of ghrelin/GHSR-1a signaling in neuropathic pain and to understand the associated mechanisms. A rat model of neuropathic pain was established by chronic constriction injury (CCI) of the sciatic nerve. Hyperalgesia and allodynia were evaluated by observing the mechanical withdrawal threshold and the thermal withdrawal latency. The expression levels of ghrelin and GHSR-1a were detected by semiquantitative reverse transcriptase-polymerase chain reaction and Western blot analysis. The levels of interleukin-1β (IL-1β), IL-6, and tumor necrosis factor-α were detected using an enzyme-linked immunosorbent assay. The expression levels of p-p38 mitogen-activated protein kinases (p38 MAPK) and nuclear factor-κB (NF-κB) p65 were determined by Western blot and immunohistochemistry analysis. Both ghrelin and GHSR-1a were expressed in the spinal dorsal horns of normal rats and were not significantly different from that of sham rats. However, rats in the CCI model group developed severe hyperalgesia and allodynia, as well as significantly downregulated expression of ghrelin and GHSR-1a. Compared with CCI model rats, intrathecal injection of ghrelin clearly delayed thermal hyperalgesia and mechanical allodynia at 3, 5, and 7 days after CCI; reduced the levels of IL-1β, IL-6, and tumor necrosis factor-α; and inhibited the phosphorylation of p38 MAPK and the activation of NF-κBp65 in the spinal dorsal horn. In addition, the effect of ghrelin could be blocked by [D-Lys]-GHRP-6, a GHSR-1a antagonist. Our present study demonstrated that ghrelin alleviated neuropathic pain through a GHSR-1a-mediated suppression of the p38 MAPK/NF-κB pathway.