GHS-R1a deficiency mitigates lipopolysaccharide-induced lung injury in mice via the downregulation of macrophage activity.

Acute respiratory distress syndrome (ARDS) is a critical illness syndrome characterized by dysregulated pulmonary inflammation. Currently, effective pharmacological treatments for ARDS are unavailable. Ghrelin, an endogenous ligand for the growth hormone secretagogue receptor type 1a (GHS-R1a), has a pivotal role in regulating energy metabolism and immunomodulation. The role of endogenous ghrelin in ARDS remains unresolved. Herein, we investigated the role of endogenous ghrelin signaling by using GHS-R1a-null (ghsr-/-) mice and lipopolysaccharide (LPS)-induced ARDS model. Ghsr-/- mice survived longer than controls after LPS-induced lung injury. Ghsr-/- mice showed lower levels of pro-inflammatory cytokines and higher oxygenation levels after lung injury. The peritoneal macrophages isolated from ghsr-/- mice exhibited lower levels of cytokines production and oxygen consumption rate after LPS stimulation. Our results indicated that endogenous ghrelin plays a pivotal role in initiation and continuation in acute inflammatory response in LPS-induced ARDS model by modulating macrophage activity, and highlighted endogenous GHS-R1a signaling in macrophage as a potential therapeutic target in this relentless disease.

Functional interaction between Ghrelin and GLP-1 regulates feeding through the vagal afferent system.

The gastrointestinal tract transmits feeding-regulatory signals to the brain via neuronal and hormonal pathways. Here we studied the interaction between the orexigenic gastric peptide, ghrelin, and the anorectic intestinal peptide, glucagon-like peptide 1 (GLP-1), in terms of feeding regulation via the vagal afferents. GLP-1 preadministration 30 min before ghrelin administration to rats and mice abolished ghrelin-induced food intake, while ghrelin preadministration abolished the anorectic effect of GLP-1. Ghrelin preadministration suppressed GLP-1-induced Fos expression in the nodose ganglia (NG). Electrophysiological assessment confirmed that the initially administered peptide abolished the vagal afferent electrical alteration induced by the subsequently administered peptide. Both the growth hormone secretagogue receptor (GHSR) and the GLP-1 receptor (GLP-1R) are co-localised in a major proportion of NG neurons that innervate the stomach. In these Ghsr+Glp1r+ neurons, ghrelin preadministration abolished the GLP-1-induced calcium response. Ghrelin generated a hyperpolarising current and GLP-1 generated a depolarising current in isolated NG neurons in a patch-clamp experiment. Ghrelin and GLP-1 potently influenced each other in terms of vagally mediated feeding regulation. This peptidergic interaction allows for fine control of the electrophysiological properties of NG neurons.

Analysis of peripheral ghrelin signaling via the vagus nerve in ghrelin receptor-restored GHSR-null mice.

The vagus nerve connects peripheral organs to the central nervous system (CNS), and gastrointestinal hormones transmit their signals to the CNS via the vagal afferent nerve. Ghrelin, a gastric-derived orexigenic peptide, stimulates food intake by transmitting starvation signals via the vagus nerve. To understand peripheral ghrelin signaling via the vagus nerve, we investigated the ghrelin receptor (GHSR)-null mouse. For this purpose, we tried to produce mice in which GHSR was selectively expressed in the hindbrain and vagus nerve. GHSR was expressed in some nodose ganglion neurons in these mice, but GHSR-expressing neurons were less abundant than in wild-type mice. Intraperitoneal administration of ghrelin did not induce food intake or growth hormone release, but did increase blood glucose levels. Our findings suggest that the abundance of GHSR-expressing neurons in the nodose ganglion is critical for peripheral administration of ghrelin-induced food intake and growth hormone release via the vagus nerve.

Restoration of metabolic inflammation-related ghrelin resistance by weight loss.

High-fat diet (HFD)-induced metabolic inflammation in the central and peripheral organs contributes to the pathogenesis of obesity. Long-term HFD blunts signaling by ghrelin, a gastric-derived orexigenic peptide, in the vagal afferent nerve via a mechanism involving in situ activation of inflammation. This study was undertaken to investigate whether ghrelin resistance is associated with progressive development of metabolic inflammation. In mice, ghrelin's orexigenic activity was abolished 2-4 weeks after the commencement of HFD (60% of energy from fat), consistent with the timing of accumulation and activation of macrophages and microglia in the nodose ganglion and hypothalamus. Calorie-restricted weight loss after 12-week HFD feeding restored ghrelin responsiveness and alleviated the upregulation of macrophage/microglia activation markers and inflammatory cytokines. HSP72, a chaperone protein, was upregulated in the hypothalamus of HFD-fed mice, potentially contributing to prevention of irreversible neuron damage. These results demonstrate that ghrelin resistance is reversible following reversal of the HFD-induced inflammation and obesity phenotypes.

NERP-2 regulates gastric acid secretion and gastric emptying via the orexin pathway.

Neuroendocrine regulatory peptide (NERP)-2 is derived from a distinct region of VGF, a neurosecretory protein originally identified as a product of a nerve growth factor-responsive gene in rat PC12 cells. Colocalization of NERP-2 with orexin-A in the lateral hypothalamus increases orexin-A-induced feeding and energy expenditure in both rats and mice. Orexigenic and anorectic peptides in the hypothalamus modulate gastric function. In this study, we investigated the effect of NERP-2 on gastric function in rats. Intracerebroventricular administration of NERP-2 to rats increased gastric acid secretion and gastric emptying, whereas peripheral administration did not affect gastric function. NERP-2-induced gastric acid secretion and gastric emptying were blocked by an orexin 1 receptor antagonist, SB334867. NERP-2 also induced Fos expression in the lateral hypothalamus and the dorsomotor nucleus of the vagus X, which are key sites in the central nervous system for regulation of gastric function. Atropine, a blocker of vagal efferent signal transduction, completely blocked NERP-2-induced gastric acid secretion. These results demonstrate that central administration of NERP-2 activates the orexin pathway, resulting in elevated gastric acid secretion and gastric emptying.

Central Insulin Action Activates Kupffer Cells by Suppressing Hepatic Vagal Activation via the Nicotinic Alpha 7 Acetylcholine Receptor.

Central insulin action activates hepatic IL-6/STAT3 signaling, which suppresses the gene expression of hepatic gluconeogenic enzymes. The vagus nerve plays an important role in this centrally mediated hepatic response; however, the precise mechanism underlying this brain-liver interaction is unclear. Here, we present our findings that the vagus nerve suppresses hepatic IL-6/STAT3 signaling via α7-nicotinic acetylcholine receptors (α7-nAchR) on Kupffer cells, and that central insulin action activates hepatic IL-6/STAT3 signaling by suppressing vagal activity. Indeed, central insulin-mediated hepatic IL-6/STAT3 activation and gluconeogenic gene suppression were impeded in mice with hepatic vagotomy, pharmacological cholinergic blockade, or α7-nAchR deficiency. In high-fat diet-induced obese and insulin-resistant mice, control of the vagus nerve by central insulin action was disturbed, inducing a persistent increase of inflammatory cytokines. These findings suggest that dysregulation of the α7-nAchR-mediated control of Kupffer cells by central insulin action may affect the pathogenesis of chronic hepatic inflammation in obesity.

One-day high-fat diet induces inflammation in the nodose ganglion and hypothalamus of mice.

A high-fat diet (HFD) induces inflammation in systemic organs including the hypothalamus, resulting in obesity and diabetes. The vagus nerve connects the visceral organs and central nervous system, and the gastric-derived orexigenic peptide ghrelin transmits its starvation signals to the hypothalamus via the vagal afferent nerve. Here we investigated the inflammatory response in vagal afferent neurons and the hypothalamus in mice following one day of HFD feeding. This treatment increased the number of macrophages/microglia in the nodose ganglion and hypothalamus. Furthermore, one-day HFD induced expression of Toll-like receptor 4 in the goblet cells of the colon and upregulated mRNA expressions of the proinflammatory biomarkers Emr1, Iba1, Il6, and Tnfα in the nodose ganglion and hypothalamus. Both subcutaneous administration of ghrelin and celiac vagotomy reduced HFD-induced inflammation in these tissues. HFD intake triggered inflammatory responses in the gut, nodose ganglion, and subsequently in the hypothalamus within 24 h. These findings suggest that the vagal afferent nerve may transfer gut-derived inflammatory signals to the hypothalamus via the nodose ganglion, and that ghrelin may protect against HFD-induced inflammation.

Diet-induced obesity causes peripheral and central ghrelin resistance by promoting inflammation.

Ghrelin, a stomach-derived orexigenic peptide, transmits starvation signals to the hypothalamus via the vagus afferent nerve. Peripheral administration of ghrelin does not induce food intake in high fat diet (HFD)-induced obese mice. We investigated whether this ghrelin resistance was caused by dysfunction of the vagus afferent pathway. Administration (s.c.) of ghrelin did not induce food intake, suppression of oxygen consumption, electrical activity of the vagal afferent nerve, phosphorylation of ERK2 and AMP-activated protein kinase alpha in the nodose ganglion, or Fos expression in hypothalamic arcuate nucleus of mice fed a HFD for 12 weeks. Administration of anti-ghrelin IgG did not induce suppression of food intake in HFD-fed mice. Expression levels of ghrelin receptor mRNA in the nodose ganglion and hypothalamus of HFD-fed mice were reduced. Inflammatory responses, including upregulation of macrophage/microglia markers and inflammatory cytokines, occurred in the nodose ganglion and hypothalamus of HFD-fed mice. A HFD blunted ghrelin signaling in the nodose ganglion via a mechanism involving in situ activation of inflammation. These results indicate that ghrelin resistance in the obese state may be caused by dysregulation of ghrelin signaling via the vagal afferent.

Neuroendocrine regulatory peptide-1 and -2 (NERPs) inhibit the excitability of magnocellular neurosecretory cells in the hypothalamus.

Neuroendocrine regulatory peptide (NERP)-1 and NERP-2 (NERPs) are novel carboxy-terminally amidated peptides derived from the neurosecretory protein VGF. NERPs are colocalized with vasopressin in the paraventricular nucleus (PVN) and the supraoptic nucleus (SON) of the hypothalamus, and suppress vasopressin secretion evoked by intracerebroventricular administration of angiotensin II (AngII) and hypertonic saline or bath administration of AngII. Magnocellular neurosecretory cells (MCNs) of the hypothalamus release vasopressin and oxytocin from their dendrites and soma. The two cell types have common electrophysiological properties in response to glutamate and AngII. We investigated the mechanisms underlying the suppressive effects of NERPs on MCNs. Microdialysis of the PVN demonstrated that NERPs suppressed glutamate release induced by AngII. A whole-cell patch-clamp study of the SON showed that NERPs suppressed the potentiation of excitatory postsynaptic currents (EPSCs) evoked by AngII without affecting the amplitude, indicating that NERPs suppressed EPSCs by a presynaptic mechanism. The suppressive effect of NERP-2, but not NERP-1, was blunted in the presence of tetrodotoxin and bicuculline, a γ-aminobutyric acid (GABA) A receptor antagonist. These results indicate that NERP-1 suppresses presynaptic glutamatergic neurons connected to MNCs, whereas NERP-2 activates GABAergic interneurons, which suppress presynaptic glutamatergic neurons; thus, both peptides suppress vasopressin release. This study demonstrates that NERPs function as inhibitory modulators of vasopressin release.

Circulating des-acyl ghrelin improves cardiovascular risk prediction in older hypertensive patients.

BACKGROUND: We aimed to assess the predictive value of circulating levels of des-acyl ghrelin, an abundant form of ghrelin in humans, for the risk of cardiovascular disease (CVD) in older hypertensive patients. We simultaneously evaluated other biomarkers, such as high-molecular-weight (HMW) adiponectin, high-sensitivity C-reactive protein (hs-CRP), and plasminogen activator inhibitor 1 (PAI-1), for their usefulness in risk prediction. METHODS: We enrolled 590 older hypertensive patients (mean age = 72.9 years; 41.0% men). The incidences of CVD, including coronary artery disease, stroke, congestive heart failure, and sudden death, were prospectively ascertained. RESULTS: During an average duration of 2.8 (SD = 0.7) years (1,653 person-years), there were 42 CVD events. Patients with CVD events had lower levels of des-acyl ghrelin at baseline than those without CVD events (median = 78.2 vs. 114.7 fmol/ml; P < 0.001). No difference was found among other biomarkers between the patients with CVD events and those without such events. The Cox proportional hazards model adjusted by covariables revealed that the hazard ratio for CVD events in patients with a 1-SD decrease of log des-acyl ghrelin was 1.8 (95% confidence interval = 1.3-2.4). Incorporation of des-acyl ghrelin in the risk model (including age, current smoking, 24-hour systolic blood pressure, preexisting CVD, and carotid intima-media thickness) improved the C statistics (from 0.683 to 0.721; P = 0.22) and resulted in a net reclassification improvement of 20.5% (P = 0.02). In contrast, HMW adiponectin, hs-CRP, and PAI-1 provided no improvement in risk prediction. CONCLUSIONS: Des-acyl ghrelin improved the prediction of CVD events in older hypertensive patients.

Elevation of muscle temperature stimulates muscle glucose uptake in vivo and in vitro.

The purpose of this study was to examine whether elevation of muscle temperature per se might be a stimulatory factor to increase muscle glucose uptake. Heat stimulation to rat hindlimbs increased glucose uptake measured in vivo in the extensor digitorum longus (EDL) and soleus muscles with a significant increase in muscle temperature. This thermal effect was observed again when glucose uptake was measured in vitro in both isolated muscles immediately after the heat stimulation in vivo. When heat stimulation was imposed on isolated EDL muscles, glucose uptake was facilitated in proportion to the increase in muscle temperature. The heat stimulation led to a significant amplification in the phosphorylation of AMP-activated protein kinase (AMPK) and Akt, and treatment with compound C, wortmannin, or LY294002 partially blocked the thermal effect on muscle glucose uptake. We provide evidence that elevation of muscle temperature per se can directly stimulate muscle glucose uptake and that this thermal effect is compound C-, wortmannin-, and LY294002-inhibitable.

Ghrelin prevents the development of experimental diabetic neuropathy in rodents.

Ghrelin is an acylated peptide discovered in gastric extracts as an endogenous ligand for the growth hormone secretagogue (GHS) receptor. This peptide increases food intake and growth hormone secretion, suppresses inflammation and oxidative stress, and promotes cell survival and proliferation. Our study investigated the pharmacological effect of ghrelin in the prevention of polyneuropathy in streptozotocin-induced diabetes mellitus in C57BL/6N mice, GHS receptor-deficient mice, and growth hormone-deficient rats. Ghrelin or desacyl-ghrelin was administered daily for four weeks immediately after disease onset. The effects of ghrelin on food intake, body weight, blood glucose and plasma insulin levels, nerve conduction velocities, temperature sensation, and 8-isoprostaglandin F2α (8-iso-PGF2α) levels were examined. We found that ghrelin administration did not change food intake, body weight gain, blood glucose levels, or plasma insulin levels in C57BL/6N mice in comparison with mice treated with saline or desacyl-ghrelin administration. Ghrelin administration, but not desacyl-ghrelin, prevented motor and sensory polyneuropathy and reduced the plasma concentrations of 8-iso-PGF2α in C57BL/6N mice. Ghrelin also prevented the reduction in nerve conduction velocities in growth hormone-deficient rats, but not in GHS receptor-knockout mice. In conclusion, ghrelin administration in a rodent model of diabetes prevented polyneuropathy, and this effect was mediated through the GHS receptor and was independent of growth hormone. The protection against the development of experimental diabetic polyneuropathy by ghrelin could be key in preventing this otherwise intractable disorder.

Neuroendocrine regulatory peptide-2 stimulates glucose-induced insulin secretion in vivo and in vitro.

Neuroendocrine regulatory peptide (NERP)-2, recently identified as a bioactive peptide involved in vasopressin secretion and feeding regulation in the central nervous system, is abundantly expressed in endocrine cells in peripheral tissues. To explore the physiological roles of NERP-2 in the pancreas, we examined its effects on insulin secretion. NERP-2 increased glucose-stimulated insulin secretion (GSIS) in a dose-dependent manner, with a lowest effective dose of 10(-7) M, from the pancreatic ß-cell line MIN6 and isolated mouse pancreatic islets. NERP-2 did not affect insulin secretion under the low-glucose conditions. Neither NERP-1 nor NERP-2-Gly (nonamidated NERP-2) stimulated insulin secretion. NERP-2 significantly augmented GSIS after intravenous administration to anesthetized rats or intraperitoneal injection to conscious mice. We detected NERP-2 in pancreatic islets, where it co-localized extensively with insulin. Calcium-imaging analysis demonstrated that NERP-2 increased the calcium influx in MIN6 cells. These findings reveal that NERP-2 regulates GSIS by elevating intracellular calcium concentrations.

Therapeutic potential of ghrelin treatment for unloading-induced muscle atrophy in mice.

Ghrelin is a growth hormone (GH) secretagogue secreted mainly from the stomach that functions in controlling muscle volume and energy homeostasis. We here studied the effects of ghrelin on unloading-induced muscle atrophy using a mouse model of hindlimb suspension (HS). Ghrelin administration during 2-week HS alleviated reductions of muscle mass in the fast-twitch fiber-rich plantaris muscle and the slow-twitch fiber-rich soleus muscle of the hindlimb. Ghrelin administration during a 5-day recovery period following 2-week HS enhanced food intake and facilitated recovery from atrophy in both muscles. Ghrelin administration normalized hypercorticosteronemia in these studies. Ghrelin's anti-muscle atrophy effect was found even under pair-feeding condition, but not in mice given des-acyl ghrelin. Insulin-like growth factor (IGF)-1 mRNA expression was significantly reduced in the atrophied plantaris muscle compared with control muscles. A single ghrelin administration to HS mice acutely increased plasma GH and also amplified phosphorylation of signal transducer and activator of transcription (STAT) 5 and increased IGF-1 mRNA expression in the plantaris muscle, but not in the soleus muscle. This study demonstrated that ghrelin stimulated the GH-STAT5-IGF-1 axis in the locally atrophied plantaris muscle, and its administration alleviated muscle atrophy and facilitated recovery from muscle atrophy. Ghrelin's effects represent a novel therapeutic paradigm for the treatment of unloading-induced muscle atrophy induced by factors such as bed rest, injury, and joint immobilization.

Significant lowering of plasma ghrelin but not des-acyl ghrelin in response to acute exercise in men.

Ghrelin, an acylated peptide produced predominantly in the stomach, stimulates feeding and growth hormone (GH) secretion via interaction with the GH secretagogue receptor. Ghrelin molecules are present in two major endogenous forms, an acylated form (ghrelin) and a des-acylated form (des-acyl ghrelin). Recent studies indicated that aerobic exercise did not change plasma total ghrelin levels, however, dynamics of circulating ghrelin and des-acyl ghrelin during aerobic exercise remains unclear. The purpose of this study is to examine the effects of moderate intensity exercise on plasma ghrelin and des-acyl ghrelin concentrations, and to investigate the relationship between ghrelin molecules and other hormonal and metabolic parameters during exercise. Nine healthy males (25.2 ± 0.5 years) exercised for 60 min at 50% of their maximal oxygen consumptions. We measured the plasma concentrations of ghrelin, des-acyl ghrelin, GH, norepinephrine (NE), epinephrine (E), dopamine (DA), insulin, and glucose. Plasma ghrelin level significantly decreased during exercise, whereas plasma des-acyl ghrelin and total ghrelin levels did not change. Plasma NE, E, DA and GH levels were significantly increased during exercise. Plasma insulin level significantly decreased during exercise, and plasma glucose levels remained steady during exercise. NE, E, DA, and GH were correlated negatively with plasma ghrelin levels. These findings suggest that acute moderate exercise may suppress ghrelin release from the stomach, decrease ghrelin O-acyltransferase activity, and/or activate ghrelin utilization in peripheral tissues and that exercise-induced ghrelin suppression may be mediated by activated adrenergic system.

Telmisartan suppresses food intake in mice via the melanocortin pathway.

SUMMARY: Telmisartan, an angiotensin type 1 receptor blocker, is widely used for the treatment of hypertension and related cardiovascular and organ damage. We here describe the effects of telmisartan on food intake and body weight using C57BL/6N mice, KKAy mice that overexpress agouti protein (a mouse model of type 2 diabetes with obesity), and mice deficient for angiotensin II-1a receptor. Telmisartan combined with a high-fat diet significantly reduced food intake and body weight gain in the three groups of mice compared with respective control animals that were fed the high-fat diet without telmisartan. Telmisartan did not induce taste aversion or affect energy expenditure. Intracerebroventricular administration of agouti-related protein, a potent antagonist of the melanocortin 3 receptor (MC3-R) and melanocortin 4 receptor (MC4-R), did not stimulate feeding in telmisartan-treated mice. Telmisartan administration enhanced the alpha-melanocyte stimulating hormone-induced suppression of food intake. This study highlights a potential role for telmisartan in hypothalamic feeding regulation, including melanocortin receptors-mediated suppression of food intake and body weight gain.:

Neuroendocrine regulatory peptide-2 regulates feeding behavior via the orexin system in the hypothalamus.

Neuroendocrine regulatory peptide (NERP)-1 and NERP-2 are derived from distinct regions of VGF, a neurosecretory protein. Vgf(-/-) mice exhibit dwarfism and hypermetabolic rates, suggesting that VGF or VGF-derived peptides play important roles in energy metabolism. Here, we examined the role of NERPs in the central regulation of feeding and energy homeostasis. We attempted to identify NERPs expressing neurons in rats by immunohistochemistry. We studied the effects of intracerebroventricular (icv) administration of NERP-2 on feeding, body temperature, oxygen consumption, and locomotor activity in rats and mice. Intracerebroventricular administration of NERP-2, but not NERP-1 or a form of NERP-2 bearing a COOH-terminal glycine extension, increased food intake in rats. We investigated the downstream signal of NERP-2 on the basis of studies of NERP-2-induced feeding with neutralization of orexins, neuropeptide Y, or agouti-related protein. NERP-2 expression localized to the lateral hypothalamus (LH) and the dorsomedial perifornical hypothalamus in rats, colocalizing with orexins that activate feeding behavior and arousal. NERP-2 administration induced Fos protein, a marker of neuronal activation, in the orexin-immunoreactive neurons. Vgf mRNA levels were upregulated in the rat LH upon food deprivation. Intracerebroventricular administration of NERP-2 also increased body temperature, oxygen consumption, and locomotor activity in rats. Treatment with anti-NERP-2 IgG decreased food intake. NERP-2-induced bioactivities could be abrogated by administration of anti-orexins IgG or orexin receptor antagonists. NERP-2 did not induce food intake or locomotor activity in orexin-deficient mice. Our findings indicate that hypothalamic NERP-2 plays a role in the control of food intake and energy homeostasis via the orexin pathway. Thus, VGF serves as a precursor of multiple bioactive peptides exerting a diverse set of neuroendocrine functions.

Plasma des-acyl ghrelin, but not plasma HMW adiponectin, is a useful cardiometabolic marker for predicting atherosclerosis in elderly hypertensive patients.

OBJECTIVE: The coming obesity epidemic in elderly persons necessitates the establishment of new and easy-to-use cardiometabolic markers to identify individuals most likely to develop atherosclerosis among hypertensives. METHODS: We measured plasma HMW adiponectin and des-acyl ghrelin levels, and carotid-artery intima-media thickness (cIMT) in 263 elderly hypertensives (mean 72.6 years; 37%men). Other cardiometabolic markers, including metabolites, inflammation, and hemostasis, were also measured. RESULTS AND CONCLUSION: Both HMW adiponectin and des-acyl ghrelin levels were inversely correlated with obesity. The HMW adiponectin level was favorably associated with glucose and lipid metabolites, PAI-1 (all P<0.05), and hs-CRP (P=0.07) after adjustment for age, sex, and BMI; however, it had no correlations with cIMT. In contrast, although there were no correlations between des-acyl ghrelin and cardiometabolic markers, except for a positive association with the nitrite/nitrate (NO(x)) level (P=0.002), des-acyl ghrelin had a significant inverse correlation with cIMT (P=0.003). A multivariable regression analysis showed that des-acyl ghrelin, but not HMW adiponectin, was significantly associated with cIMT after adjusting for age, obesity, sex, smoking, 24-h BP, and other cardiometabolic factors (beta=-0.178, P=0.001). Moreover, the increased risk of cIMT among those with abdominal obesity compared with non-obesity (0.833+/-0.185 mm vs. 0.782+/-0.163 mm, P=0.019) was explained by the elevated 24-h BP and reduced des-acyl ghrelin level, but not by other cardiometabolic parameters. These associations were unchanged after adding NO(x) to the model. In conclusion, the des-acyl ghrelin level is a useful cardiometabolic marker for predicting atherosclerosis in elderly hypertensives, and the pathologic pathway linking these factors is independent of its NO bioactivity.

Characterization of obestatin in rat and human stomach and plasma, and its lack of acute effect on feeding behavior in rodents.

Obestatin is a 23-amino acid peptide, initially isolated from rat stomach as an endogenous ligand for the orphan G-protein-coupled receptor. Obestatin is derived from proteolytic cleavage of a 117-amino acid precursor, preproghrelin. Ghrelin increases food intake, body weight, and gastric emptying, whereas obestatin has the opposite effects. In this study, we characterized obestatin in both rat and human stomach, and investigated the peptide's effect on feeding behavior. Using reversed-phase high-performance liquid chromatography coupled with RIAs specific for rat and human obestatin, we detected a very small amount of obestatin, compared with ghrelin, in the gastric fundi. The ratios of obestatin to ghrelin are 0.0039 and 1.94% respectively in the rat and human gastric fundi. In humans, plasma obestatin accounted for 5.21% of the ghrelin concentration, whereas it was undetectable in rat plasma. Plasma ghrelin concentration decreased after a meal in normal subjects, whereas obestatin concentration did not change. When administered centrally or peripherally, obestatin did not suppress food intake in either free-feeding or fasted rodents. Administration of obestatin did not antagonize ghrelin-induced feeding. These findings indicate that obestatin is present at very low levels compared with ghrelin in both rat and human, and has no acute effect on feeding behavior.