Role of central and peripheral ghrelin in the mechanism of gastric mucosal defence

An insight into the multifunctional role of ghrelin and structure activity relationship studies of ghrelin receptor ligands with clinical trials

Ghrelin is a multifunctional gastrointestinal acylated peptide, primarily synthesized in the stomach and regulates the secretion of growth hormone and energy homeostasis. It plays a central role in modulating the diverse biological, physiological and pathological functions in vertebrates. The synthesis of ghrelin receptor ligands after the finding of growth hormone secretagogue developed from Met-enkephalin led to reveal the endogenous ligand ghrelin and the receptors. Subsequently, many peptides, small molecules and peptidomimetics focusing on the ghrelin receptor, GHS-R1a, were derived. In this review, the key features of ghrelin's structure, forms, its bio-physiological functions, pathological roles and therapeutic potential have been highlighted. A few peptidomimetics and pseudo peptide synthetic perspectives have also been discussed to make ghrelin receptor ligands, clinical trials and their success.

Protective and Healing Effects of Ghrelin and Risk of Cancer in the Digestive System

Ghrelin is an endogenous ligand for the ghrelin receptor, previously known as the growth hormone secretagogue receptor. This hormone is mainly produced by endocrine cells present in the gastric mucosa. The ghrelin-producing cells are also present in other organs of the body, mainly in the digestive system, but in much smaller amount. Ghrelin exhibits a broad spectrum of physiological effects, such as stimulation of growth hormone secretion, gastric secretion, gastrointestinal motility, and food intake, as well as regulation of glucose homeostasis and bone formation, and inhibition of inflammatory processes. This review summarizes the recent findings concerning animal and human data showing protective and therapeutic effects of ghrelin in the gut, and also presents the role of growth hormone and insulin-like growth factor-1 in these effects. In addition, the current data on the possible influence of ghrelin on the carcinogenesis, its importance in predicting the risk of developing gastrointestinal malignances, as well as the potential usefulness of ghrelin in the treatment of cancer, have been presented.

Protective Factors of the Gastric and Duodenal Mucosa: An Overview

The structural and functional integrity of the gastric and duodenal mucosa represents equilibrium between aggressive factors and protective mechanisms. Mucus-buffers-phospholipid layer as pre-epithelial barrier, enhanced by prostaglandins and epidermal growth factor, remains a vanguard of mucosal protection. It maintains a neutral pH at the surface epithelial luminal interface, facing luminal pH dropping to 1.0, i.e., hydrogen ion concentration gradient equal 1,000,000. The surface epithelial cells, elaborating mucins, buffers, phospholipids, prostaglandins, trefoil peptides, peptide growth factor and their receptors, heat shock proteins, cathelicidins, and β-defensins form the second line of defense. Endothelium exerts mucosal protection through production of potent vasodilators like nitric oxide and prostacyclins and through release of angiogenic growth factors, securing adequate blood flow and representing the third and an ultimate line of mucosal protection. This microcirculation is instrumental for supply of oxygen, nitric oxide, hydrogen sulfide and removal of ad hoc generated toxic substances as well as for continuous mucosal cell renewal from progenitor cells, secured by growth factors accompanied by survivin preventing early apoptosis.

Relationship between ghrelin and gastrointestinal diseases

Ghrelin is a newly found 28-amino acid brain-gut peptide, which is mainly secreted by the gastric mucosa. It has two forms, acyl-ghrelin and des-acyl ghrelin, and the former is the major active form. Ghrelin is an endogenous ligand for the growth hormone secretagogue receptor and plays an important role in regulating food intake, gastric acid secretion, gastrointestinal motility, gastric mucosa protection, and inhibition of inflammatory reaction in paracrine, autocrine and endocrine manners. Recent studies have found that ghrelin levels are abnormal in a variety of gastrointestinal diseases, such as Helicobacter pylori infection, peptic ulcer, functional dyspepsia, inflammatory bowel disease, pancreatitis, tumors and so on, suggesting that ghrelin may be involved in the pathogenesis of these diseases. Ghrelin may become an index for disease diagnosis and prognosis evaluation and a new target for treatment of gastrointestinal diseases.

Pharmacological and alimentary alteration of the gastric barrier

The gastric barrier contains several lines of defence which protect the epithelium from harmful microbes and toxins. Pre-mucosal defence mechanisms include secreted acid (HCl 0.1 mmol/L) and pepsin, which are capable of denaturing tissue. A tightly adherent mucous layer provides the next line of defence, and physically separates any potentially hazardous substance in the lumen from the mucosal surface. Apical secretion of HCO3(-) maintains a non-acidic microenvironment at the mucosal surface. Membrane-bound phospholipids repel soluble toxins, and sulphydryls scavenge reactive oxygen species. However, when noxious agents overwhelm these mechanisms, the epithelium is damaged. Herein, we discuss the pathological and physiological basis for several disease states which are associated with a breakdown in one or more components of the gastric barrier, including: Helicobacter pylori-associated gastritis, atrophic gastritis, stress-related mucosal disease, age-related gastropathy and portal hypertensive gastropathy. The effect of non-steroidal anti-inflammatory drugs and proton pump inhibitors on the gastric mucosa, is explored. Finally, we outline the alterations in mucosal defence caused by alcohol, caffeine, minerals and vitamins.

Ghrelin in gastrointestinal diseases

Ghrelin is an endogenous ligand of the growth hormone secretagogue receptor (GHSR). Upon binding to its receptor, Ghrelin can produce a variety of biological effects, such as promoting the release of growth hormone and maintaining energy balance. Besides, it also promotes gastrointestinal motility, increases gastric acid secretion, and is involved in the genesis of tumors. This article reviews the role of Ghrelin in gastrointestinal system disease.

The effects of ghrelin on colonic anastomosis healing in rats

OBJECTIVES

In addition to its roles in the stimulation of growth hormone secretion and the regulation of appetite and metabolism, ghrelin exerts immunomodulatory, anti-inflammatory and antioxidant actions in several organ systems. In this study, we investigated the effects of ghrelin on the healing of experimental colonic anastomoses.

METHODS

Wistar rats were randomly divided into two groups (n = 10 in each). A segment of colon was excised, and an end-to-end anastomosis was performed in the distal colon. The Ghrelin Group received 10 ng/kg/day IP ghrelin for seven days postoperatively, whereas the Control Group received an identical volume of saline. On the seventh postoperative day, the anastomotic bursting pressures and hydroxyproline levels were measured, and adhesion formation around the anastomoses was examined. Histopathological analyses were performed to evaluate inflammatory cell infiltration, fibroblast infiltration, collagen density and neovascularization.

RESULTS

In the Ghrelin Group, the bursting pressure and hydroxyproline levels were significantly higher than in the Control Group. The adhesion formation scores were lower in the Ghrelin Group than in the Control Group. Although the inflammatory cell infiltration was diminished in the Ghrelin Group, the degrees of fibroblast infiltration, collagen density and neovascularization were not significantly different between the groups.

CONCLUSION

Our results indicate that ghrelin improves the healing of colonic anastomoses in rats.

Brainstem neuropeptides and vagal protection of the gastric mucosal against injury: role of prostaglandins, nitric oxide and calcitonin-gene related peptide in capsaicin afferents

Earlier experimental studies indicated that the integrity of vagal pathway was required to confer gastric protection against damaging agents. Several peptides located in the brainstem initially identified to influence vagal outflow to the stomach, as assessed by electrophysiological approach or by vagal dependent alterations of gastric secretory and motor function, were investigated for their influence in the vagal regulation of the resistance of the gastric mucosa to injury. Thyrotropin releasing hormone (TRH), or its stable TRH analog, RX-77368, injected at low doses into the cisterna magna or the dorsal motor nucleus (DMN) was the first peptide reported to protect the gastric mucosa against ethanol injury through stimulation of vagal cholinergic pathways, inducing the release of gastric prostaglandins/nitric oxide (NO) and the recruitment of efferent function of capsaicin sensitive afferent fibers containing calcitonin-gene related peptide (CGRP). Activation of endogenous TRH-TRH1 receptor signaling located in the brainstem plays a role in adaptive gastric protection against damaging agents. Since then, an expanding number of peptides, namely peptide YY, CGRP, adrenomedullin, amylin, glugacon-like peptide, opioid peptides acting on µ, δ1 or δ2 receptors, nocicpetin, nocistatin, ghrelin, leptin and TLQP-21, a peptide derived from VGF prohormone, have been reported to act in the brainstem to afford gastric protection against ethanol injury largely through similar peripheral effectors mechanisms than TRH. Therefore gastric prostaglandins and CGRP/NO pathways represent a common final mechanism through which brain peptides confer vagally mediated gastroprotection against injury. A better understanding of brain circuitries through which these peptides are released will provide new strategies to recruit integrated and multifaceted gastroprotective mechanisms.

Gastric mucosal damage in water immersion stress: Mechanism and prevention with GHRP-6

AIM: To investigate the mechanism of gastric mucosal demage induced by water immersion restraint stress (WRS) and its prevention by growth hormone releasing peptide-6 (GHRP-6).

METHODS: Male Wistar rats were subjected to conscious or unconscious (anesthetized) WRS, simple restraint (SR), free swimming (FS), non-water fluid immersion, immersion without water contact, or rats were placed in a cage surrounded by sand. To explore the sensitivity structures that influence the stress reaction besides skin stimuli, a group the rats had their eyes occluded. Cervical bilateral trunk vagotomy or atropine injection was performed in some rats to assess the parasympathetic role in mucosal damage. Gastric mucosal lesions, acid output and heart rate variability were measured. Plasma renin, endothelin-1 and thromboxane B2 and gastric heat shock protein 70 were also assayed. GHRP-6 was injected [intraperitoneal (IP) or intracerebroventricular (ICV)] 2 h before the onset of stress to observe its potential prevention of the mucosal lesion.

RESULTS: WRS for 6 h induced serious gastric mucosal lesion [lesion area, WRS 81.8 ± 6.4 mm²vs normal control 0.0 ± 0.0 mm², P < 0.01], decreased the heart rate, and increased the heart rate variability and gastric acid secretion, suggesting an increase in vagal nerve-carrying stimuli. The mucosal injury was inversely correlated with water temperature (lesion area, WRS at 35 °C 56.4 ± 5.2 mm²vs WRS at 23 °C 81.8 ± 6.4 mm², P < 0.01) and was consciousness-dependent. The injury could not be prevented by eye occlusion, but could be prevented by avoiding contact of the rat body with the water by dressing it in an impermeable plastic suit. When water was replaced by vegetable oil or liquid paraffin, there were gastric lesions in the same grade of water immersion. When rat were placed in a cage surrounded by sand, there were no gastric lesions. All these data point to a remarkable importance of cutenuous information transmitted to the high neural center that by vagal nerves reaching the gastric mucosa. FS alone also induced serious gastric injury, but SR could not induce gastric injury. Bilateral vagotomy or atropine prevented the WRS-induced mucosal lesion, indicating that increased outflow from the vagal center is a decisive factor in WRS-induced gastric injury. The mucosal lesions were prevented by prior injection of GHRP-6 via IP did, but not via ICV, suggesting that the protection is peripheral, although a sudden injection is not equivalent to a physiological release and uptake, which eventually may affect the vagal center.

CONCLUSION: From the central nervous system, vagal nerves carry the cutaneous stimuli brought about by the immersion restraint, an experimental model for inducing acute gastric erosions. GHRP-6 prevents the occurrence of these lesions.

Sleeve gastrectomy provides a better control of diabetes by decreasing ghrelin in the diabetic Goto-Kakizaki rats

AIM

Sleeve gastrectomy (SG) and modified duodenal jejunal bypass (MDJB) were compared as procedures for glucose control. We aim to form the initial conclusions with respect to the possibility of (1) whether gastric fundus exclusion is essential for the control of diabetes and (2) application as a low morbidity procedure.

MATERIALS AND METHODS

SG and MDJB were performed on 10- to 12-week-old Goto-Kakizaki rats that spontaneously develop type 2 diabetes. Rats were observed for 36 weeks after surgery, and glucose, insulin, glucagons-like peptide-1 (GLP-1), glucose tolerate, insulin sensitivity, cholesterol, triglycerides, and free fatty acid levels were measured.

RESULTS

Apart from distinct weight loss of SG and MDJB after 1 month compared with sham-operated rats (P < 0.001), SG showed strikingly improved blood glucose levels and significantly decreased Ghrelin secretion (P < 0.001). Furthermore, SG resulted in a shorter operative time (P < 0.01) and postoperative recovery time (P < 0.01) than MDJB group.

CONCLUSIONS

SG shows better control in terms of glucose tolerance and other measurements. This study provides direct evidence that SG possesses better improvement of diabetes by reduction of Ghrelin.

Gastroprotective action of Cochinchina momordica seed extract is mediated by activation of CGRP and inhibition of cPLA(2)/5-LOX pathway

Cochinchina momordica seed extract (SKMS10), which is composed of the major compounds momordica saponins, has been evaluated for its gastroprotective effects in rat models of acute gastric mucosal damage. Ethanol and water immersion restraint stress (WRS) induced gastric damage, including hemorrhages and edema, was significantly attenuated by pretreatment with SK-MS10. In addition, SK-MS10 reduced increases of mucosal myeloperoxidase (MPO), IL-1β, and TNFα levels and the expression of cPLA(2), and 5-LOX induced by ethanol or WRS. SK-MS10 also increased hexosamine, adherent mucus, and the expression of MUC5AC. Furthermore, SK-MS10 enhanced the mucosal expression of the CGRP gene and its serum levels.N(G)-methyl L-arginine (L-NMMA) or capsaicin desensitization reversed the SK-MS10-induced gastroprotection effect. These results suggest that SK-MS10 is a gastroprotective agent against acute gastric mucosal damage by suppressing proinflammatory cytokines, downregulating cPLA(2), 5-LOX, and increasing the synthesis of mucus. Furthermore, CGRP-NO pathway was found to play an important role in these gastroprotective effects of SK-MS10.

Gastric mucosal defense and cytoprotection: bench to bedside

The gastric mucosa maintains structural integrity and function despite continuous exposure to noxious factors, including 0.1 mol/L HCl and pepsin, that are capable of digesting tissue. Under normal conditions, mucosal integrity is maintained by defense mechanisms, which include preepithelial factors (mucus-bicarbonate-phospholipid "barrier"), an epithelial "barrier" (surface epithelial cells connected by tight junctions and generating bicarbonate, mucus, phospholipids, trefoil peptides, prostaglandins (PGs), and heat shock proteins), continuous cell renewal accomplished by proliferation of progenitor cells (regulated by growth factors, PGE(2) and survivin), continuous blood flow through mucosal microvessels, an endothelial "barrier," sensory innervation, and generation of PGs and nitric oxide. Mucosal injury may occur when noxious factors "overwhelm" an intact mucosal defense or when the mucosal defense is impaired. We review basic components of gastric mucosal defense and discuss conditions in which mucosal injury is directly related to impairment in mucosal defense, focusing on disorders with important clinical sequelae: nonsteroidal anti-inflammatory drug (NSAID)-associated injury, which is primarily related to inhibition of cyclooxygenase (COX)-mediated PG synthesis, and stress-related mucosal disease (SRMD), which occurs with local ischemia. The annual incidence of NSAID-associated upper gastrointestinal (GI) complications such as bleeding is approximately 1%-1.5%; and reductions in these complications have been demonstrated with misoprostol, proton pump inhibitors (PPIs) (only documented in high-risk patients), and COX-2 selective inhibitors. Clinically significant bleeding from SRMD is relatively uncommon with modern intensive care. Pharmacologic therapy with antisecretory drugs may be used in high-risk patients (eg, mechanical ventilation >or=48 hours), although the absolute risk reduction is small, and a decrease in mortality is not documented.

Ghrelin improves burn-induced multiple organ injury by depressing neutrophil infiltration and the release of pro-inflammatory cytokines

Mechanisms of burn-induced skin and remote organ injury involve oxidant generation and the release of pro-inflammatory cytokines. In this study the possible antioxidant and anti-inflammatory effects of ghrelin were evaluated in a rat model of thermal trauma. Wistar albino rats were exposed to 90 degrees C bath for 10 s to induce thermal trauma. Ghrelin, was administered subcutaneously (10 ng/kg/day) after the burn injury and repeated twice daily. Rats were decapitated at 6 h and 48 h after burn injury and blood was collected for the analysis of pro-inflammatory cytokines (TNF-alpha and IL-1beta), lactate dehydrogenase (LDH) activity and antioxidant capacity (AOC). In skin, lung and stomach tissue samples malondialdehyde (MDA) and glutathione (GSH) levels, myeloperoxidase (MPO) and Na(+)-K(+)-ATPase activity were measured in addition to the histological analysis. DNA fragmentation ratio in the gastric mucosa was also evaluated. Burn injury caused significant increase in both cytokine levels, and LDH activity, while plasma AOC was found to be depleted after thermal trauma. On the other hand, in tissue samples the raised MDA levels, MPO activity and reduced GSH levels, Na(+)-K(+)-ATPase activity due to burn injury were found at control levels in ghrelin-treated groups, while DNA fragmentation in the gastric tissue was also reduced. According to the findings of the present study, ghrelin possesses a neutrophil-dependent anti-inflammatory effect that prevents burn-induced damage in skin and remote organs and protects against oxidative organ damage.

Ghrelin, des-acyl ghrelin and obestatin: three pieces of the same puzzle

The major active product of ghrelin gene is a 28-amino acid peptide acylated at the serine 3 position with an octanoyl group, called simply ghrelin. Ghrelin has a multiplicity of physiological functions, affecting GH release, food intake, energy and glucose homeostasis, gastrointestinal, cardiovascular, pulmonary and immune function, cell proliferation and differentiation and bone physiology. Nevertheless, recent developments have shown that ghrelin gene can generate various bioactive molecules besides ghrelin, mainly des-acyl ghrelin and obestatin, obtained from alternative splicing or from extensive post-translational modification. Although their receptors have not yet been identified, they have already proven to be active, having intriguingly subtle but opposite physiological actions to ghrelin. This suggests the existence of a novel endocrine system with multiple effector elements which not only may have opposite actions but may regulate the action of each other. In this review, we summarize the steps which lead to the production of the different ghrelin gene products and examine the most significant differences between them in terms of structure and actions.

Effects of vitamin E, vitamin C, and selenium on gastric fundus in cadmium toxicity in male rats

Cadmium (Cd) is a highly toxic metal. It has an indirect role in the generation of various free radicals. Antioxidants such as vitamin E, vitamin C, and selenium are important for preventing the damage caused by reactive oxygen species. This study was undertaken to examine the effect of acute cadmium and/or antioxidants on serum lipid metabolism, tissue glutathione, and lipid peroxidation (LPO) levels, and ghrelin and metallothionein production in the gastric fundus mucosa of rats. Cd (2 mg/kg/day CdCl(2)) was administered to rats for 8 days, intraperitoneally. Vitamin E (250 mg /kg/day) + vitamin C (250 mg/kg/day) + sodium selenate (0.25 mg /kg/day) were administered to rats orally at the same time. The animals were treated by antioxidants 1 h prior to treatment with Cd every day. Gastric tissue homogenates were used for protein and glutathione and LPO levels. Phospholipid and total lipid levels were determined in serum. Gastric fundus sections examined for histopathological changes and by immunohistochemistry for expression of ghrelin and metallothionein. In the group treated with Cd, degenerative changes such as discontinuity in the surface epithelium were observed. The degenerative changes induced by Cd were decreased in the group given vitamin E + vitamin C + selenium. There was no significant change in ghrelin- and metallothionein-immunoreactive cells in fundus mucosa. Stomach glutathione levels insignificantly decreased in the Cd groups, but in the Cd group given antioxidant, stomach glutathione levels were significantly increased. Serum phospholipid and total lipid levels were significantly increased in the Cd groups. On the other hand, treatment with antioxidants reversed these effects. These results indicate that antioxidants partly prevent the toxicity of Cd in rat gastric fundus.

Ghrelin alleviates biliary obstruction-induced chronic hepatic injury in rats

BACKGROUND

Reactive oxygen species and oxidative stress are implicated in hepatic stellate cell activation and liver fibrosis, which are initiated by recruitment of inflammatory cells and by activation of cytokines.

OBJECTIVE

The possible anti-oxidant and anti-inflammatory effects of ghrelin were evaluated in a hepatic fibrosis model in rats with bile duct ligation (BDL).

METHODS

Under anesthesia, bile ducts of Sprague Dawley rats were ligated, and half of the rats were subcutaneously administered with ghrelin (10 ng/kg/day) and the rest with saline for 28 days. Sham-operated control groups were administered saline or ghrelin. On the 28th day of the study, rats were decapitated and malondialdehyde (MDA) content--an index of lipid peroxidation, and myeloperoxidase (MPO) activity--an index of neutrophil infiltration--were determined in the liver tissues. Oxidant-induced tissue fibrosis was determined by collagen contents, while the hepatic injury was analyzed microscopically. Serum aspartate aminotransferase (AST), alanine aminotransferase (ALT) levels and lactate dehydrogenase (LDH) levels were determined to assess liver function and tissue damage, respectively. Pro-inflammatory cytokines; TNF-alpha, IL-1beta and IL-6 were also assayed in plasma samples.

RESULTS

In the saline-treated BDL group, hepatic MDA levels, MPO activity and collagen content were increased (p<0.001), suggesting oxidative organ damage, as confirmed histologically. In the ghrelin-treated BDL group, however, all of the oxidant responses were reversed significantly (p<0.05-p<0.001). Serum AST, ALT, LDH levels, and cytokines were elevated in the BDL group as compared to the control group, while this increase was significantly decreased by ghrelin treatment.

CONCLUSION

Owing to the anti-inflammatory and anti-oxidant effect as demonstrated in our study, it is possible to speculate that exogenously administered ghrelin may possess an antifibrotic effect against biliary obstruction-induced liver fibrosis. Thus, it seems likely that ghrelin may be of potential therapeutic value in protecting the liver fibrosis and oxidative injury due to biliary obstruction.

Alcohol-induced disruption of endocrine signaling

This article contains the proceedings of a symposium at the 2006 ISBRA meeting in Sydney Australia, organized and cochaired by Martin J. Ronis and Thomas M. Badger. The presentations were (1) Effect of long-term ethanol consumption on liver injury and repair, by Jack R. Wands; (2) Alcohol-induced insulin resistance in liver: potential roles in regulation of ADH expression, ethanol clearance, and alcoholic liver disease, by Thomas M. Badger; (3) Chronic gestational exposure to ethanol causes brain insulin and insulin-like growth factor resistance, by Suzanne M de la Monte; (4) Disruption of IGF-1 signaling in muscle: a mechanism underlying alcoholic myopathy, by Charles H. Lang; (5) The role of reduced plasma estradiol and impaired estrogen signaling in alcohol-induced bone loss, by Martin J. Ronis; and (6) Short-term influence of alcohol on appetite-regulating hormones in man, by Jan Calissendorff.

Physiological, pathological and potential therapeutic roles of ghrelin

Ghrelin, a hormone that is produced mainly by the stomach, was identified originally as the endogenous ligand of the growth hormone secretagogue (GHS) receptor. Ghrelin might also be synthesized in other organs, where it might have autocrine or paracrine effects. GHS receptors are present in tissues other than the hypothalamus and pituitary, which indicates that ghrelin has other effects in addition to stimulating the release of growth hormone. Recently, it has been suggested that ghrelin might be involved in the pathogenesis of many diseases and be a therapeutic target in these diseases. Here, we provide an overview of the physiological effects of ghrelin and of its pathological and potential therapeutic roles.

Ghrelin inhibits apoptosis in hypothalamic neuronal cells during oxygen-glucose deprivation

Ghrelin is an endogenous ligand for the GH secretagogue receptor, produced and secreted mainly from the stomach. Ghrelin stimulates GH release and induces positive energy balances. Previous studies have reported that ghrelin inhibits apoptosis in several cell types, but its antiapoptotic effect in neuronal cells is unknown. Therefore, we investigated the role of ghrelin in ischemic neuronal injury using primary hypothalamic neurons exposed to oxygen-glucose deprivation (OGD). Here we report that treatment of hypothalamic neurons with ghrelin inhibited OGD-induced cell death and apoptosis. Exposure of neurons to ghrelin caused rapid activation of ERK1/2. Ghrelin-induced activation of ERK1/2 and the antiapoptotic effect of ghrelin were blocked by chemical inhibition of MAPK, phosphatidylinositol 3 kinase, protein kinase C, and protein kinase A. Ghrelin attenuated OGD-induced activation of c-Jun NH2-terminal kinase and p-38 but not ERK1/2. We also investigated ghrelin regulation of apoptosis at the mitochondrial level. Ghrelin protected cells from OGD insult by inhibiting reactive oxygen species generation and stabilizing mitochondrial transmembrane potential. In addition, ghrelin-treated cells showed an increased Bcl-2/Bax ratio, prevention of cytochrome c release, and inhibition of caspase-3 activation. Finally, in vivo administration of ghrelin significantly reduced infarct volume in an animal model of ischemia. Our data indicate that ghrelin may act as a survival factor that preserves mitochondrial integrity and inhibits apoptotic pathways.