A-like cells in the rat stomach contain ghrelin and do not operate under gastrin control

Low gastric acid and high plasma gastrin in high-anxiety Wistar Kyoto rats

OBJECTIVE

Wistar Kyoto (WKY) rats are more susceptible to stress-evoked ulcerations than Sprague-Dawley (SPD) rats. We have already demonstrated that gastrin cells are more active and ghrelin cells less active in WKY rats than in SPD rats. The purpose of this study was to compare endocrine cell activity and gastric acid output in WKY and SPD rats.

MATERIAL AND METHODS

Gastric acid output was determined in conscious rats with gastric fistula. Plasma gastrin and ghrelin levels were measured after an overnight fast. Acid secretagogues (gastrin, histamine and carbachol) were given by continuous subcutaneous infusion.

RESULTS

The volume of gastric juice, and the acidity and acid output were all significantly lower (p <0.05) in fasted WKY rats than in fasted SPD rats. Gastrin evoked a 4-fold (p <0.01) and 3-fold (p <0.05) increase in gastric acid output in SPD rats and WKY rats, respectively. Histamine raised the acid output 1.6-fold in SPD rats (p=0.06) and 3-fold in WKY rats (p <0.05), while carbachol failed to affect the acid output (weak increase, p >0.05). Fasting plasma ghrelin levels were 2-fold higher in SPD rats than in WKY rats (p <0.01) while fasting gastrin levels were 10-fold higher in WKY rats than in SPD rats (p <0.05). Neither the parietal-cell density nor the oxyntic mucosal thickness differed between the two strains.

CONCLUSIONS

The results of the present study suggest that a high gastrin cell activity in WKY rats is secondary to a low gastric acidity. Whether the high gastrin cell activity is linked to susceptibility to stress ulcer in WKY rats warrants further investigation.

Obestatin/ghrelin cells in normal mucosa and endocrine tumours of the stomach

OBJECTIVE

Obestatin and ghrelin are derived from the same gene and co-expressed in the same endocrine cells. Vesicular monoamine transporter-2 (VMAT-2), a marker for enterochromaffin-like (ECL) cells, is considered to be expressed in ghrelin cells. The aim was to establish if the two peptides and the transporter are co-expressed, both in normal gastric mucosa and in gastric endocrine tumours.

DESIGN

An immunohistochemical study was performed on gastric biopsy material and on surgical specimens from 63 patients with gastric endocrine tumours and from individuals with normal gastric mucosa. Cells displaying obestatin immunoreactivity were examined regarding co-localization with ghrelin and VMAT-2. Both single- and double-immunostaining techniques were applied. Obestatin concentration in blood was measured in a subgroup of these patients. The results were correlated to various clinico-pathological parameters.

RESULTS

In the normal mucosa, obestatin/ghrelin-immunoreactive cells rarely co-expressed VMAT-2. In most tumour tissue specimens, only a fraction of neoplastic cells displayed immunoreactivity to obestatin, and these cells always co-expressed ghrelin. Neoplastic obestatin-/ghrelin-IR cells invariably expressed VMAT-2, except for two ghrelinomas. The obestatin concentrations in blood were consistently low and did not correlate to clinico-pathological data.

CONCLUSIONS

Obestatin and ghrelin immunoreactivity always occurred in the same endocrine cells in the gastric mucosa but these cells only occasionally co-expressed VMAT-2, opposite to the findings in tumours. These results indicate that endocrine cells expressing obestatin and ghrelin mainly differ from VMAT-2 expressing cells (ECL-cells) and can develop into pure ghrelinomas. Plasma concentrations of obestatin did not correlate to cellular expression.

Characterization of a novel ghrelin cell reporter mouse

Ghrelin is a hormone that influences many physiological processes and behaviors, such as food intake, insulin and growth hormone release, and a coordinated response to chronic stress. However, little is known about the molecular pathways governing ghrelin release and ghrelin cell function. To better study ghrelin cell physiology, we have generated several transgenic mouse lines expressing humanized Renilla reniformis green fluorescent protein (hrGFP) under the control of the mouse ghrelin promoter. hrGFP expression was especially abundant in the gastric oxyntic mucosa, in a pattern mirroring that of ghrelin immunoreactivity and ghrelin mRNA. hrGFP expression also was observed in the duodenum, but not in the brain, pancreatic islet, or testis. In addition, we used fluorescent activated cell sorting (FACS) to collect and partially characterize highly enriched populations of gastric ghrelin cells. We suggest that these novel ghrelin-hrGFP transgenic mice will serve as useful tools to better understand ghrelin cell physiology.

Ghrelin's role on gastrointestinal tract cancer

Ghrelin is a recently identified 28-amino-acid peptide, with pituitary growth hormone releasing activities in humans and other mammals. In mammals, ghrelin plays a variety of roles, including influence on food intake, gastric motility, and acid secretion of the gastrointestinal tract. It is mainly secreted from the stomach mucosa, but it is also expressed widely in other tissues - in normal and malignant conditions - and, therefore, ghrelin may exert such variable endocrine and paracrine effects, as autocrine and/or paracrine function in cancer. Ghrelin's actions are mediated via its receptor, known as growth hormone secretagogue receptor (GHS-R), type 1a and 1b. Several endocrine and non-endocrine cancers, such as gastro-entero-pancreatic carcinoids, colorectal neoplasms, pituitary adenomas, pulmonary and thyroid tumours, as well as lung, breast, and pancreatic carcinomas express ghrelin at both mRNA and protein levels. In the current review, we summarise the available so far data with regard to: (a) the structure of the ghrelin molecule and its receptor; (b) its tissue contribution in physiologic and neoplasmatic conditions; and (c) ghrelin's possible role in carcinogenesis; specifically, in the area of gastrointestinal tract cancer. The aim of the present study is to determine whether or not ghrelin promotes the proliferation rate of the gastrointestinal tract (GIT) tumours.

Effect of antrectomy in hypergastrinaemic female Japanese cotton rats

OBJECTIVE

Female Japanese cotton rats become hypoacidic and hypergastrinaemic from age 2 months and later develop gastric carcinomas in the oxyntic mucosa. Previous studies have demonstrated that carcinogenesis can be halted by a gastrin receptor antagonist and that carcinomas can be induced by a histamine-2 receptor antagonist or partial corpectomy, both of which induce hypergastrinaemia. The aim of the present study was to examine the effect of antrectomy in female cotton rats.

MATERIAL AND METHODS

The animals were either antrectomized (Group 1) or sham-operated (Group 2) 2 months after detection of hypergastrinaemia and terminated 4 months after operation. A third group was antrectomized at age 2 months while still normo-acidic (Group 3) and terminated 6 months after operation.

RESULTS

Antrectomy after 2 months of hypergastrinaemia prevented the development of carcinoma compared with in sham-operated animals, whereas some of the animals that were antrectomized at 2 months of age also developed carcinomas. In Groups 1 and 2 as well as in animals developing carcinomas in Group 3, there was marked hyperplasia of neuroendocrine cells in the oxyntic mucosa expressing chromogranin A, vesicular monoamine transporter (VMAT)-2, ghrelin and somatostatin. Gastrin-positive cells were found adjacent to neoplastic areas in the oxyntic mucosa.

CONCLUSIONS

The removal of antral gastrin by antrectomy halts carcinogenesis in cotton rats, but other mechanisms may also play a role.

Serum ghrelin in infants with protein-energy malnutrition

BACKGROUND

Ghrelin is an appetite and weight physiologic controller. The question is whether there is a relation between ghrelin and protein-energy malnutrition (PEM). Our aim was to assess serum ghrelin in these patients and its relation to different patient variables.

METHODS

A cross-sectional study was conducted on 30 PEM infants (12 marasmic=Ia, 10 kwashiorkor=Ib and 8 marasmic kwashiorkor=Ic) and 15 age and sex matched controls (II). Plasma ghrelin was measured in all subjects using radioimmunoassay with thorough medical history and clinical assessment.

RESULTS

The mean serum ghrelin levels were significantly higher among the 3 patient subgroups than controls with no significant inter-subgroup differences. The presence of intestinal parasitic infestations or edema, type of milk feeding and gender had no significant effects on serum ghrelin levels.

CONCLUSION

Serum ghrelin is elevated in PEM as an adapting consequence of the malnutrition rather than a primary event. Although this elevation may not be helpful to correct the growth failure because of deficient nutrients, it may prove to have a role in the catch up phenomenon after the recovery. Further research should be directed toward therapeutic trials of ghrelin in the recovery phase.

Ghrelin restores 'lean-type' hunger and energy expenditure profiles in morbidly obese subjects but has no effect on postgastrectomy subjects

OBJECTIVE

To examine the effects of ghrelin on appetite and energy expenditure in lean, obese and postgastrectomy subjects.

DESIGN

A randomized, double-blind, placebo-controlled study.

PATIENTS

Nine lean subjects (mean body mass index (BMI) 23.5+/-3 kg/m(2)) and nine morbidly obese subjects (mean BMI 51.4+/-10 kg/m(2)) and eight postgastrectomy subjects (mean BMI 22.4+/-1.0 kg/m(2)).

INTERVENTIONS

Subjects were infused with either intravenous ghrelin (5 pmol kg(-1) min(-1)) or saline over 270 min. They were given a fixed energy breakfast followed by a free buffet lunch towards the end of the infusion.

MAIN OUTCOME MEASURES

Visual analogue scales were used to record hunger and energy expenditure was measured by indirect calorimetry.

RESULTS

Ghrelin increased energy intake at the buffet lunch in lean subjects (a 41% increase, P<0.01) and obese subjects (35% increase, P=0.04) but not in postgastrectomy subjects. Lean subjects showed a characteristic preprandial rise and postprandial fall in hunger scores, which was exaggerated by ghrelin infusion. Obese subjects showed little variation in hunger scores, but a 'lean-type' pattern was restored when given exogenous ghrelin. Ghrelin had no effect on resting metabolic rate but did increase respiratory quotient (RQ) in obese subjects. Ghrelin also increased RQ variability over time in all three groups (ANOVA, P<0.001).

CONCLUSIONS

Hunger scores are abnormal in the obese, perhaps because of impaired ghrelin secretion. The effect of ghrelin in restoring normal hunger profiles in the obese suggests causality, confirming an important role in eating behaviour. Ghrelin also increases RQ in obese humans and increased RQ variability in all groups. This suggests that ghrelin regulates substrate utilization and may promote metabolic flexibility.

Obestatin, obesity and diabetes

The high prevalence of obesity and diabetes will lead to higher rates of morbidity and mortality. It is well known that ghrelin plays a potential role in obesity and diabetes. Obestatin, a novel 23 amino acid amidated peptide encoded by the same gene that encodes ghrelin, was initially reported to have opposite actions to ghrelin in the regulation of food intake, emptying of the stomach and body weight. Recent work suggests that obestatin also regulate beta-cell survival and insulin secretion. The ghrelin-obestatin system is, therefore, a promising target for the developing of new drugs for the treatment of obesity and diabetes. This review summarizes the interrelationship between obestatin, obesity and diabetes.

Gastric secretion

PURPOSE OF REVIEW

This review summarizes the past year's literature regarding the regulation and assessment of gastric acid secretion.

RECENT FINDINGS

Gastric acid secretion is regulated by biologic agents produced and released by enteroendocrine cells and neurons as well as by exogenously administered substances and infection. Too much acid can lead to gastroesophageal reflux disease, peptic ulcer disease, and stress-related erosion/ulcer disease. Too little acid can interfere with the absorption of certain nutrients, predispose to enteric infection, and interfere with the absorption of some medications. Gastrin, histamine, gastrin-releasing peptide, ghrelin, orexin, and glucocorticoids stimulate whereas leptin, glucagon-like peptide 1, and Helicobacter pylori inhibit acid secretion. Helicobacter pylori inhibits the transcriptional activity of HK-ATPase, the proton pump of the parietal cell.

SUMMARY

A better understanding of the pathways and mechanisms regulating gastric acid secretion should lead to improved management of patients with acid-induced disorders as well as those who secrete too little acid.

Vagotomy and accompanying pyloroplasty down-regulates ghrelin mRNA but does not affect ghrelin secretion

In this study, we have examined how the lack of vagus activity affects the long-term secretion of total and active ghrelin. We subjected mice to sham-operation, pyloroplasty or vagotomy and pyloroplasty. The study lasted for 2 weeks, during which body weight development and daily food intake was monitored. At the end of the study, the mice were sacrificed, and serum and fundus were collected. Measurements of total and active serum ghrelin revealed no difference between the surgical groups and sham-operated mice, despite the fact that fundic ghrelin mRNA was down-regulated. The results presented here suggest that the vagus activity is not required for the long-term secretion of neither total nor active ghrelin in mice. They also suggest that fundic ghrelin mRNA expression is affected by pyloroplasty and vagotomy but that this effect does not translate into changes in ghrelin levels in the circulation.

Structure and function of ghrelin

The endogenous ligand for growth-hormone secretagogue receptor (GHS-R) was purified from the stomach and we named it "ghrelin", after a word root ("ghre") in Proto-Indo-European languages meaning "grow", since ghrelin has potent growth hormone (GH) releasing activity. In addition, ghrelin stimulates appetite by acting on the hypothalamic arcuate nucleus, a region known to control food intake. Ghrelin is orexigenic; it is secreted from the stomach and circulates in the blood stream under fasting conditions, indicating that it transmits a hunger signal from the periphery to the central nervous system. Taking into account all these activities, ghrelin plays important roles for maintaining growth hormone release and energy homeostasis in vertebrates. The diverse functions of ghrelin raise the possibility of its clinical application for GH deficiency, eating disorder, gastrointestinal disease, cardiovascular disease, osteoporosis and aging, etc.

Effects of intraamygdaloid microinjections of acylated-ghrelin on liquid food intake of rats

Ghrelin (Ghr) has two main forms in the blood: the acylated (A-Ghr) and non-acylated (NA-Ghr) Ghr. A-Ghr was discovered as a potent growth hormone (GH) secretion increasing substance acting on GH secretagouge receptor (GHS-R) type 1a. A-Ghr facilitates food intake after its i.p., i.c.v. or direct hypothalamic application. Immunohistological assays identified projections of ghrelinergic neurons to the basolateral nucleus (ABL) of the amygdala (AMY). A-Ghr injected into the hypothalamus caused c-Fos overexpression in the AMY area that has an important role in food intake and body weight regulation. In separate experiments, liquid food intake of male wistar rats was measured after bilateral intraamygdalar or bilateral i.c.v. administration of A-Ghr (25, 50, 100, 250, and 500 ng/side or 500 and 1000 ng/side, A-Ghr dissolved in 0.15 M sterile NaCl/0.4 microl or 1 microl, respectively). In the ABL, A-Ghr microinjections in the 50-250 ng dose range resulted in significant decrease of food intake. The 25 and 500 ng had no effect. Action of 50 ng (14.83 pmol) or 100 ng (30.16 pmol) A-Ghr was eliminated by 15 ng (16.13 pmol) or 30 ng (32.25 pmol) GHS-R antagonist (D-Lys3-GHRP-6) pretreatment. The administration of 30 ng D-Lys3-GHRP-6 in itself had no influence on feeding. I.c.v. applied 1000 ng A-Ghr increased liquid food intake. Our results are the first ones reporting that A-Ghr injected into the ABL resulted in a decrease of liquid food consumption, within a limited dose range. This is a receptor-linked effect because it was eliminated by a GHS-R specific antagonist.

Ghrelin: a new peptide regulating the neurohormonal system, energy homeostasis and glucose metabolism

Identification of ghrelin started with the discovery of growth hormone secretagogues, continued with the description of ghrelin receptors and ended with the elucidation of the chemical structure of ghrelin. However, several issues concerning the role of ghrelin in physiological and pathophysiological processes are still under investigation. Most of the ghrelin produced in the body is secreted in the stomach, but it is also expressed in the hypothalamus, pituitary, pancreas, intestine, kidney, heart and gonads. Ghrelin stimulates growth hormone secretion via growth hormone secretagogue receptors. Ghrelin secretion in the stomach depends on both acute and chronic changes in nutritional status and energy balance. Current data support the hypothesis that the stomach, in addition to its important role in digestion, not only influences pituitary hormone secretion but, via ghrelin production, it also sends orexigenic (appetite increasing) signals to hypothalamic nuclei involved in the regulation of energy homeostasis. In addition to these main effects, ghrelin influences insulin secretion and glucose metabolism and it may exert potentially important effects on cardiovascular and gastrointestinal functions. Because of its effects on a large number of physiological functions, ghrelin may be involved in the pathomechanism of several human disorders, including disturbances of appetite, energy homeostasis and glucose metabolism. Further research might lead to a better understanding of the pathophysiology of ghrelin and might provide more effective therapy for the above disorders.

Ghrelin in pathological conditions

The recently identified gastric hormone ghrelin was initially described as a natural Growth Hormone Secretagogue Receptor ligand. Apart from ghrelin's first discovered action, which was the stimulation of Growth Hormone release, implications for many other functions have been reported. It seems that ghrelin exhibits an important role in conditions related to processes regulating nutrition, body composition and growth, as well as heart, liver, thyroid or kidney dysfunction. In this review, current available knowledge about ghrelin's role in various pathological conditions is presented.

Bariatric surgery for extreme adolescent obesity: indications, outcomes, and physiologic effects on the gut-brain axis

OBJECTIVE

This review will summarize current indications, limitations and outcomes of bariatric surgery in adolescents, as well as provide an overview of the physiologic effects of bariatric surgery on enteric hormones involved in regulating appetite, satiation and maintenance of weight.

RESULTS

Extreme obesity (BMI≥99 percentile) now affects 4% of children and adolescents in the United States. Traditional dietary and behavioral weight management methods have no demonstrated efficacy for extremely obese children and adolescents, in contrast with bariatric surgery which has produced significant and sustainable weight loss and associated improvements in comorbid diseases for the extremely obese. Roux-en-Y gastric bypass (RYGB) and laparoscopic adjustable gastric banding (LAGB) are the most commonly performed bariatric surgical procedures in adolescents, but vertical sleeve gastrectomy may be a promising new option for selected extremely obese adolescents. A mean weight loss of 37-40% is achieved in adolescents after RYGB, with LAGB showing similar results, albeit attained at a slower rate.

CONCLUSION

Alterations in the enteric hormones involved in the gut-brain axis that regulates appetite and energy expenditure may play a role in both the anorexigenic and weight-reducing effects of certain bariatric surgical procedures. In particular, RYGB induces a rise in both fasting and post-prandial peptide tyrosine-tyrosine which could contribute to the more rapid and greater degree of weight loss than is seen with LAGB. Limitations of bariatric surgery however include the potential for post-operative morbidity and mortality, as well as possible weight regain in a small proportion of patients.

Effects of sucrose, glucose and fructose on peripheral and central appetite signals

In the Western world, consumption of soft drinks has increased the last three decades and is partly responsible for the epidemic-like increase in obesity. Soft drinks, originally sweetened by sucrose, are now sweetened by other caloric sweeteners, such as fructose. In this study, we investigated the short-term effect of sucrose, glucose or fructose solutions on food intake and body weight in rats, and on peripheral and central appetite signals. Rats received water containing either of the sugars and standard rat chow for two weeks. Rats receiving water alone and standard chow were controls. All rats offered the sugar solutions increased their total caloric intake. The increased caloric intake occurred despite the fact that the rats offered either of the sugar solutions consumed less chow. As a consequence of the increased caloric intake, the sugar-drinking rats had elevated serum levels of free fatty acids, triglycerides and cholesterol. In addition, consuming sugar solutions resulted in increased serum leptin, decreased serum PYY and down-regulated hypothalamic NPY mRNA. Serum ghrelin was increased in rats receiving fructose solution. Moreover, consumption of sucrose or fructose solution resulted in up-regulated hypothalamic CB1 mRNA. Hypothalamic POMC mRNA was down-regulated in rats receiving glucose or fructose. In conclusion, consumption of glucose, sucrose or fructose solution results in caloric overconsumption and body weight gain through activation of hunger signals and depression of satiety signals as well as activation of reward components. The weight-promoting effect of these sugar solutions may possibly be ameliorated by the down-regulation of NPY mRNA and increased serum leptin.

Control of gastric acid secretion in health and disease

Recent milestones in the understanding of gastric acid secretion and treatment of acid-peptic disorders include the (1) discovery of histamine H(2)-receptors and development of histamine H(2)-receptor antagonists, (2) identification of H(+)K(+)-ATPase as the parietal cell proton pump and development of proton pump inhibitors, and (3) identification of Helicobacter pylori as the major cause of duodenal ulcer and development of effective eradication regimens. This review emphasizes the importance and relevance of gastric acid secretion and its regulation in health and disease. We review the physiology and pathophysiology of acid secretion as well as evidence regarding its inhibition in the management of acid-related clinical conditions.

Distribution of obestatin and ghrelin in human tissues: immunoreactive cells in the gastrointestinal tract, pancreas, and mammary glands

Obestatin and ghrelin are two peptides derived from the same prohormone. It is well established that ghrelin is produced by endocrine cells in the gastric mucosa. However, the distribution of human obestatin immunoreactive cells is not thoroughly characterized. A polyclonal antibody that specifically recognizes human obestatin was produced. Using this antibody and a commercial antibody vs ghrelin, the distribution of obestatin and ghrelin immunoreactive cells was determined in a panel of human tissues using immunohistochemistry. The two peptides were detected in the mucosa of the gastrointestinal tract, from cardia to ileum, and in the pancreatic islets. Interestingly, epithelial cells in the ducts of mammary glands showed distinct immunoreactivity for both ghrelin and obestatin. By double immunofluorescence microscopy, it was shown that all detected cells were immunoreactive for both peptides. Furthermore, the subcellular localization of obestatin and ghrelin was essentially identical, indicating that obestatin and ghrelin are stored in the same secretory vesicles.

The gastrointestinal hormone ghrelin modulates inhibitory neurotransmission in deep laminae of mouse spinal cord dorsal horn

Ghrelin is mainly described for its effects on feeding behavior and metabolism. However, central nervous system distribution of its receptor [type 1a GH secretagogue receptor (GHSR)] and modulation of neurotransmission in the hypothalamus suggest broader effects than originally predicted. Systemically administrated ghrelin inhibits inflammatory pain after behavioral observations. Therefore, we investigated the expression and function of type 1a GHSR in mouse spinal cord by molecular biology, biochemistry, histology, and electrophysiology. The mRNA and protein were detected in tissue extracts by RT-PCR and Western blotting. In situ, receptor mRNA and immunoreactivity were localized to cell bodies within the medial aspect of the deep dorsal horn. Patch clamp recordings on laminae IV-VI demonstrated that bath-applied ghrelin (100 nm) induced a strong increase of spontaneous gamma-aminobutyric acid/glycine-mediated current frequency (463 +/- 93% of the control) and amplitude (150 +/- 16% of the control) in about 60% of recorded neurons. Specificity of type 1a GHSR activation was confirmed by the lack of effect of the deacylated form of ghrelin (des-acyl-ghrelin) and after preincubation with the specific receptor antagonist [d-Lys(3)]GHRP-6. In the presence of tetrodotoxin, the effect of the peptide was strongly reduced, mainly indicating an action potential-dependent mechanism. The functional link between ghrelin and pain was confirmed by inhibition in vitro of the c-fos response to capsaicin activation of nociceptive fibers, after quantification of Fos-immunoreactive nuclei in laminae IV-VI. Our results are the first demonstration of the presence of functional type 1a GHSRs in the spinal cord and indicate that ghrelin may exert antinociceptive effects by directly increasing inhibitory neurotransmission in a subset of deep dorsal horn neurons.

Does ghrelin explain accelerated gastric emptying in the early stages of diabetes mellitus?

During the early stages of diabetes, gastric emptying is often accelerated, rather than delayed. The mechanism of accelerated gastric emptying in diabetes has not been fully studied. A recent study showed that plasma ghrelin levels were elevated in diabetes. As postprandial antropyloric coordination plays an important role in mediating solid gastric emptying, we hypothesize that the elevated plasma ghrelin levels increase postprandial antropyloric coordination to accelerate emptying in the early stages of diabetes. To test this hypothesis, rats were made diabetic by streptozotocin (STZ; 50 mg/kg) injection, and, 2 wk later, pre- and postprandial plasma ghrelin levels, antropyloric coordination, and solid gastric emptying were determined. In control rats, plasma ghrelin levels were immediately reduced after feeding. In contrast, plasma ghrelin levels remained within the fasted levels in STZ rats after feeding. In STZ rats, gastric emptying was significantly accelerated (77.4 +/- 3.2%, n = 6), compared with that of control rats (58.8 +/- 2.5%, n = 6, P < 0.05). Treatments with anti-ghrelin antibodies attenuated accelerated gastric emptying in STZ rats (50.1 +/- 3.5%, n = 6, P < 0.05), while having little effect in vehicle control rats. The incidence of postprandial antropyloric coordination was significantly increased in STZ rats, compared with that of control rats (P < 0.05). Treatments with anti-ghrelin antibodies suppressed this enhanced antropyloric coordination in STZ rats. Our study suggests that elevated endogenous ghrelin enhances antropyloric coordination, which accelerates gastric emptying in the early stages of diabetes.

Ghrelin immunoreactive cells in gastric endocrine tumors and their relation to plasma ghrelin concentration

GOALS

Our aim was to elucidate the incidence and distribution pattern of ghrelin-immunoreactive (IR) cells in various types of human gastric endocrine tumors, and their surrounding mucosa, and relate the findings to total ghrelin concentrations in plasma.

BACKGROUND

It has been demonstrated previously, that ghrelin-IR cells are present not only in normal human gastric oxyntic mucosa, but also in all types of enterochromaffinlike (ECL) cell carcinoids (ECL-CCs), and in mucosal regions affected by ECL cell hyperplasia.

STUDY

Forty-eight gastric endocrine tumors were included in the study: 32 type I ECL-CCs, 3 type II, 9 type III, 1 non-ECL-CC, and 3 poorly differentiated endocrine carcinomas. The tumors were analyzed immunohistochemically with antibodies raised versus chromogranin A, synaptophysin, serotonin, somatostatin, vesicular monoamine transporter 2 and ghrelin. Total ghrelin in plasma was measured in 20 patients, using a commercial radioimmunoassay kit.

RESULTS

Ghrelin-IR cells were found in all types I and II ECL-CCs but in only a few cases of the other tumors. Ghrelin-IR cells were also found among the hyperplastic endocrine cells in the mucosa surrounding types I and II, where they showed diffuse, linear, nodular and adenomatoid hyperplasia patterns. In type III ECL-CCs and poorly differentiated endocrine carcinomas, only diffuse and linear ghrelin-IR cell hyperplasia was present in the oxyntic mucosa in about half of the cases, whereas the mucosa of the non-ECL-CC did not show this feature.

CONCLUSIONS

Despite the frequent occurrence of ghrelin-IR cells in both the neoplastic parenchyma and the oxyntic mucosa, plasma total ghrelin concentrations remained within the reference range and can therefore not be used as a clinical marker to identify ghrelin expressing ECL-CCs or ghrelin cell hyperplasia.

Peripheral injection of ghrelin induces Fos expression in the dorsomedial hypothalamic nucleus in rats

Peripheral ghrelin has been shown to act as a gut-brain peptide exerting a potent orexigenic effect on food intake. The dorsomedial nucleus of the hypothalamus (DMH) is innervated by projections from other brain areas being part of the network of nuclei controlling energy homeostasis, among others NPY/AgRP-positive fibers arising from the arcuate nucleus (ARC). The aim of the study was to determine if peripherally administered ghrelin affects neuronal activity in the DMH, as assessed by Fos expression. The number of Fos positive neurons was determined in the DMH, paraventricular nucleus of the hypothalamus (PVN), ARC, ventromedial hypothalamic nucleus (VMH), nucleus of the solitary tract (NTS) and in the area postrema (AP) in non-fasted Sprague-Dawley rats in response to intraperitoneally (ip) injected ghrelin (3 nmol/rat) or vehicle (0.15 M NaCl). Peripheral ghrelin induced a significant increase in the number of Fos-ir positive neurons/section compared with vehicle in the ARC (mean+/-SEM: 49+/-2 vs. 23+/-2 neurons/section, p=0.001), PVN (69+/-5 vs. 34+/-3, p=0.001), and DMH (142+/-5 vs. 83+/-5, p<0.001). Fos-ir positive neurons were mainly localized within the ventral part of the DMH. No change in Fos expression was observed in the VMH (53+/-8 vs. 48+/-6, p=0.581), NTS (42+/-2 vs. 40+/-3, p=0.603), and in the AP (7+/-1 vs. 5+/-1, p=0.096). Additional double-labelling with anti-Fos and anti-AgRP revealed that Fos positive neurons in the DMH were encircled by a network of AgRP-ir positive fibers. These data indicate that peripheral ghrelin activates DMH neurons and that NPY-/AgRP-positive fibers may be involved in the response.

Characterization of obestatin- and ghrelin-producing cells in the gastrointestinal tract and pancreas of rats: an immunohistochemical and electron-microscopic study

Both ghrelin and obestatin are derived from preproghrelin by post-translational processing. We have morphologically characterized the cells that produce obestatin and ghrelin in new-born and adult Sprague-Dawley rats that were freely fed, fasted, or subjected to gastric bypass surgery or reserpine treatment. Tissue samples collected from the gastrointestinal tract and pancreas were examined by double-immunofluorescence staining, immunoelectron microscopy, and conventional electron microscopy. Obestatin was present in the stomach, duodenum, jejunum, colon, and pancreas. In the stomach, differences were noted in the development of obestatin- and preproghrelin-immunreactive (IR) cells on the one hand and ghrelin-IR cells on the other, particularly 2 weeks after birth. Preproghrelin- and obestatin-IR cells were more numerous than ghrelin-IR cells in the stomach, suggesting the lack of ghrelin in some A-like cells. Most obestatin-producing cells in the stomach were distributed in the basal part of the oxyntic mucosa; these cells co-localized with chromogranin A (pancreastatin) and vesicle monoamine transporters type 1 and 2, but not with serotonin or histidine decarboxylase. Immunoelectron microscopy revealed the obestatin- and ghrelin-producing cells to be A-like cells, characterized by numerous highly electron-dense granules containing ghrelin and obestatin. Some granules exhibited an even electron density with thin electron-lucent halos, suggestive of monoamines. Feeding status, gastric bypass surgery, and reserpine treatment had no obvious effect on the A-like cells. In the pancreas, obestatin was present in the peripheral part of the islets, with a distribution distinct from that of glucagon-producing A cells, insulin-producing beta cells, and cells producing pancreatic polypeptide Y. Thus, obestatin and ghrelin co-localize with an anticipated monoamine in A-like cells in the stomach, and obestatin is found in pancreatic islets.

Peripheral ghrelin interacts with orexin neurons in glucostatic signalling

Ghrelin interactions with glycemia in appetite control as well as the potential mechanisms involving the orexin and melanin-concentrating hormone (MCH) neurons in the orexigenic ghrelin signals were investigated by using a specific anti-ghrelin antibody (AGA). Our results confirm that peripheral ghrelin is an important signal in meal initiation and appetite. Employing immunohistochemistry techniques, we found that c-fos positive neurons in the lateral hypothalamus (LH) and perifornical area (PFA) increased after insulin or 2-deoxyglucose administration. Moreover, we have also demonstrated that peripheral ghrelin blockade by the AGA, reduces the orexigenic signal induced by insulin and 2-DG administration probably partly producing a decrease of c-fos immunoreactivity in the LH and PFA as well as a lower activation of orexin neurons. In contrast, the c-fos positive MCH neurons were not apparently affected. In summary, our findings suggest that peripheral ghrelin plays an important role in regulatory "glucostatic" feeding mechanisms by means of its role as a "hunger" signal affecting the LH and PFA areas, which may contribute to energy homeostasis through orexin neurons.

Genetically engineered mice: a new paradigm to study gastric physiology

PURPOSE OF REVIEW

To summarize key aspects from recent research as well as review articles on the topic of genetic mouse models, particularly in knockout mice, that have considerably contributed to understanding the pathways and mechanisms underlying gastric physiology.

RECENT FINDINGS

A series of knockout mouse models has proven to be invaluable in elucidating the mechanism and validating the current model of acid secretion. The interaction between the gastrin-histamine and cholecystokinin-somatostatin pathways was identified using the genetic approach as being critical in regulating acid secretion. Curiously, neither ghrelin nor ghrelin receptor knockout mice displayed the expected lean phenotype. Importantly, the study of obestatin in GPR39 knockout mice could be misleading, as zinc rather than obestatin is the endogenous ligand for GPR39. The physiological roles of ghrelin and obestatin have yet to be confirmed using knockout mouse models.

SUMMARY

The knockout mouse continues to serve as an excellent model to dissect the complexity of the mechanism of gastric acid secretion and to study the physiological importance of gastric ghrelin.

In vivo and in vitro antioxidant activity of ghrelin: Attenuation of gastric ischemic injury in the rat

BACKGROUND AND AIM

Gherlin, an endogenous ligand for the growth hormone secretagogue receptor (GHS-R), is produced by stomach cells. It regulates food intake, gastric secretion and motility. However, its role as a protective agent in gastric ischemia/reperfusion (I/R) injury has not yet been investigated. Therefore, the objectives of the present study were to: (i) test the in vivo effect of peripherally administered ghrelin on gastric I/R-induced lesions in rats; and (ii) investigate in vitro the effect of ghrelin on reactive oxygen species (ROS) production by human polymorphoneuclear (PMN) cells.

METHODS

The present study was carried out on three groups of rats (six per group): control (sham-operated), I/R (clamping of celiac artery for 30 min and reperfusion for 1 h), and I/R + ghrelin (200 ng/kg i.v., 15 min before ischemia and before reperfusion, respectively). Histological assessment of hematoxylin and eosin stained sections was performed and immunostaining with inducible nitric oxide (iNOS) antibody were performed on a gastric paraffin embedded section. Oxidative stress markers thiobarbituric acid reactive substance (TBARS) and glutathione (GSH) were measured in gastric tissue homogenates. Serum lactic acid dehydrogenase (LDH) was determined. Tumor necrosis factor-alpha (TNF-alpha) was assayed in gastric tissue homogenate. Gastric permeability was assessed calorimetrically using Evans blue dye. In vitro studies were carried out on isolated human PMN cells incubated with ghrelin and tested for ROS generation as measured by chemiluminecence (CL).

RESULTS

Peripheral administration of ghrelin attenuated gastric injury by reducing ulceration, tissue congestion, cellular infiltration and vascular permeability. Serum level of LDH and tissue content of TNF-alpha were markedly reduced. A decrement in TBARS and an increment in GSH were observed. Ghrelin treatment attenuated iNOS protein expression which was upregulated by gastric ischemic injury. In vitro studies showed for the first time that ghrelin inhibited ROS generation by human PMN in a dose-dependent manner.

CONCLUSIONS

These results provide evidence that peripherally administered ghrelin protects against gastric I/R injury. We also demonstrated that this protection is possibly accomplished through the antioxidant activity of ghrelin observed in vivo and in vitro.

Serum ghrelin as a marker of atrophic body gastritis in patients with parietal cell antibodies

AIM

Autoimmune gastritis is frequently associated with autoimmune thyroiditis and other organ-specific autoimmune diseases, and may lead to atrophic body gastritis (ABG). We studied the diagnostic use of the measurement of serum ghrelin compared with other markers of gastric damage in predicting the presence of ABG in patients with autoimmune gastritis.

METHODS

We studied 233 patients with autoimmune gastritis and 211 control subjects. All patients and control subjects were screened for circulating parietal cell antibodies (PCAs) and were tested for serum ghrelin, gastrin, pepsinogen I and II, and anti-Helicobacter pylori antibody levels. A total of 52 patients and 28 control subjects underwent a gastric endoscopy.

RESULTS

In PCA/positive patients, mean (+/-sd) serum ghrelin levels were significantly lower (238 +/- 107 pmol/liter), and mean (+/-sd) serum gastrin levels were significantly higher (81.2 +/- 128.3 ng/ml), with respect to PCA/negative patients (282 +/- 104 pmol/liter and 20.7 +/- 13.3 ng/ml, respectively; P < 0.0001). Serum ghrelin and gastrin levels were inversely correlated (P = 0.004). A total of 40 patients had ABG documented by the gastric biopsy (90% in PCA/positive patients and 10% in PCA/negative patients). The receiver operating characteristic curve analysis revealed that a cutoff value for serum ghrelin of 188 pmol/liter was associated with the highest sensitivity and specificity (97.3 and 100%, respectively) in detecting gastric atrophy and was superior to gastrin (P = 0.012), PCA (P = 0.002), and the pepsinogen I/II ratio (P = 0.016) measurements.

CONCLUSIONS

Our study demonstrates that ghrelin secretion is negatively affected by autoimmune gastritis, and its serum level represents the most sensitive and specific noninvasive marker for selecting patients at high risk for ABG.

Plasma acylated ghrelin levels are higher in patients with chronic atrophic gastritis

OBJECTIVES

Ghrelin is mainly produced by the endocrine cells of the gastric oxyntic mucosa. For this reason we decided to investigate the modification of the circulating levels not only of total but also of acylated ghrelin in a series of patients with chronic atrophic gastritis.

DESIGN

Twenty-five patients with chronic atrophic gastritis and 25 healthy subjects were studied. In all 50 subjects gastrin and total and acylated ghrelin levels were evaluated. All patients underwent endoscopy with multiple biopsies, and the possibility of Helicobacter pylori infection was investigated.

RESULTS

Significantly higher acylated ghrelin levels (82.8 +/- 61.3 vs. 35.1 +/- 17.1 pmol/l), acylated/total ghrelin ratio (0.422 +/- 0.202 vs. 0.152 +/- 0.085) and gastrin levels (1071 +/- 816 vs. 66 +/- 22 ng/l) were observed in the 25 patients with chronic atrophy than in the healthy subjects. Otherwise, no significant relationships were found when total ghrelin was correlated with the presence of atrophy, or with gastrin levels. In the healthy subjects, but not in the patients, acylated and total ghrelin levels were significantly higher in female than in male patients.

CONCLUSIONS

The increase in acylated ghrelin levels and in the acylated/total ghrelin ratio in patients with atrophy of the body and fundus can be explained by hypothesizing an increase in the acylating process in the presence of gastric atrophy. It suggests that there may be a compensatory increase in plasma active ghrelin concentration in response to gastric atrophy, a condition which causes a loss of ghrelin-producing cells and an increase in gastric pH.

The effect of luminal ghrelin on pancreatic enzyme secretion in the rat

Ghrelin, a 28-amino-acid peptide produced predominantly by oxyntic mucosa has been reported to affect the pancreatic exocrine function but the mechanism of its secretory action is not clear. The effects of intraduodenal (i.d.) infusion of ghrelin on pancreatic amylase outputs under basal conditions and following the stimulation of pancreatic secretion with diversion of pancreato-biliary juice (DPBJ) as well as the role of vagal nerve, sensory fibers and CCK in this process were determined. Ghrelin given into the duodenum of healthy rats at doses of 1.0 or 10.0 microg/kg increased pancreatic amylase outputs under basal conditions or following the stimulation of pancreatic secretion with DPBJ. Bilateral vagotomy as well as capsaicin deactivation of sensory fibers completely abolished all stimulatory effects of luminal ghrelin on pancreatic exocrine function. Pretreatment with lorglumide, a CCK(1) receptor blocker, reversed the stimulation of amylase release produced by intraduodenal application of ghrelin. Intraduodenal ghrelin at doses of 1.0 or 10.0 microg/kg increased plasma concentrations of CCK and ghrelin. In conclusion, ghrelin given into the duodenum stimulates pancreatic enzyme secretion. Activation of vagal reflexes and CCK release as well as central mechanisms could be implicated in the stimulatory effect of luminal ghrelin on the pancreatic exocrine functions.

The ghrelin system in acinar cells: localization, expression, and regulation in the exocrine pancreas

OBJECTIVES

Ghrelin and its receptor are expressed abundantly in the stomach and pituitary. Recently, a ghrelin system, consisting of both ligand and receptor, has also been found to exist in the endocrine cells of pancreatic islets. This ghrelin system may play a role in regulating insulin secretion and glucose homeostasis. The aim of the present study was to investigate whether a functional ghrelin system also exists in the exocrine pancreas.

METHODS

Precise localization and expression of ghrelin and its receptor in rat pancreatic acinar cells were examined by immunocytochemistry and Western blot, whereas messenger RNA levels were examined by semiquantitative reverse transcription-polymerase chain reaction. The roles of physiological and pathophysiological conditions, such as gastric acid inhibition, starvation, and acute pancreatitis, in regulation of ghrelin and its receptor were also examined.

RESULTS

Both ghrelin and its receptor were detected, at both protein and messenger RNA levels, in the acinar cells of the exocrine pancreas. Ghrelin receptor expression was up-regulated by gastric acid inhibition and down-regulated by acute pancreatitis, whereas levels remained unchanged after food deprivation. In contrast, ghrelin expression did not exhibit significant changes in any condition.

CONCLUSIONS

Our data indicate that a ghrelin system exists in the acinar cells of the exocrine pancreas. This system is subject to regulation by physiological and pathophysiological stimuli and may thus regulate exocrine functions by paracrine and/or autocrine mechanisms.

Proghrelin-derived peptides influence the secretion of insulin, glucagon, pancreatic polypeptide and somatostatin: a study on isolated islets from mouse and rat pancreas

Proghrelin, the precursor of the orexigenic and adipogenic peptide hormone ghrelin, is synthetized in endocrine (A-like) cells in the gastric mucosa. During its cellular processing, proghrelin gives rise to the 28-amino acid peptide desacyl ghrelin, which after octanoylation becomes active acyl ghrelin, and to the 23-amino acid peptide obestatin, claimed to be a physiological opponent of acyl ghrelin. This study examines the effects of the proghrelin products, alone and in combinations, on the secretion of insulin, glucagon, pancreatic polypeptide (PP) and somatostatin from isolated islets of mice and rats. Surprisingly, acyl ghrelin and obestatin had almost identical effects in that they stimulated the secretion of glucagon and inhibited that of PP and somatostatin from both mouse and rat islets. Obestatin inhibited insulin secretion more effectively than acyl ghrelin. In mouse islets, acyl ghrelin inhibited insulin secretion at low doses and stimulated at high. In rat islets, acyl ghrelin inhibited insulin secretion in a dose-dependent manner but the IC(50) for the acyl ghrelin-induced inhibition of insulin release was 7.5 x 10(-8) M, while the EC(50) and IC(50) values, with respect to stimulation of glucagon release and to inhibition of PP and somatostatin release, were in the 3 x 10(-12)-15 x 10(-12) M range. The corresponding EC(50) and IC(50) values for obestatin ranged from 5 x 10(-12) to 20 x 10(-12) M. Desacyl ghrelin per se did not affect islet hormone secretion. However, at a ten times higher concentration than acyl ghrelin (corresponding to the ratio of the two peptides in circulation), desacyl ghrelin abolished the effects of acyl ghrelin but not those of obestatin. Acyl ghrelin and obestatin affected the secretion of glucagon, PP and somatostatin at physiologically relevant concentrations; with obestatin this was the case also for insulin secretion. The combination of obestatin, acyl ghrelin and desacyl ghrelin in concentrations and proportions similar to those found in plasma resulted in effects that were indistinguishable from those induced by obestatin alone. From the data it seems that the effects of endogenous, circulating acyl ghrelin may be overshadowed by obestatin or blunted by desacyl ghrelin.

Hypothalamic gene expression following ghrelin therapy to gastrectomized rodents

We investigated whether ghrelin depletion (by gastrectomy surgery) and/or treatment/replacement with the gastric hormone ghrelin alters the expression of key hypothalamic genes involved in energy balance, in a manner consistent with ghrelin's pro-obesity effects. At 2 weeks after surgery mice were treated with ghrelin (12 nmol/mouse/day, sc) or vehicle for 8 weeks. Gastrectomy had little effect on the expression of these genes, with the exception of NPY mRNA in the arcuate nucleus that was increased. Ghrelin treatment (to gastrectomized and sham mice) increased the mRNA expression of orexigenic peptides NPY and AgRP while decreasing mRNA expression of the anorexigenic peptide POMC. Two weeks gavage treatment with the ghrelin mimetic, MK-0677, to rats increased NPY and POMC mRNA in the arcuate nucleus and MCH mRNA in the lateral hypothalamus. Thus, while predicted pro-obesity ghrelin signalling pathways were activated by ghrelin and ghrelin mimetics, these were largely unaffected by gastrectomy.

Ghrelin and motilin are cosecreted from a prominent endocrine cell population in the small intestine

CONTEXT

Ghrelin is a novel hormone produced mainly in the gastric body. Hitherto, mapping studies of ghrelin cells covering the entire gastrointestinal (GI) tract in humans have been lacking. Furthermore, the phenotype of extragastric ghrelin cells is not known.

OBJECTIVE

The objective of the study was to perform a detailed mapping with specimens from all parts of the GI tract, and colocalization studies to phenotype ghrelin cells along the tract. In addition, mapping of ghrelin cells was performed in porcine GI tract, and the plasma profiles of ghrelin and motilin in blood from the porcine intestine were measured.

DESIGN

Biopsies from patients were obtained during gastroscopy or surgery. Ghrelin cell density and phenotyping was assessed with immunocytochemistry, in situ hybridization, and immunogold electron microscopy. Plasma ghrelin and motilin levels were measured in pigs, fitted with cannulas in the mesenteric vein.

RESULTS

The upper small intestine is unexpectedly rich in ghrelin cells, and these cells contribute to circulating ghrelin. Ghrelin and motilin are coproduced in the same cells in the duodenum and jejunum of both species, and ghrelin and motilin are stored in all secretory granules of such cells in humans, indicating cosecretion. The plasma profiles of ghrelin and motilin in pig were parallel, and a correlation between ghrelin and motilin (r(2) = 0.22; P < 0.001) was evident in intestinal blood.

CONCLUSIONS

The upper small intestine is an important source of ghrelin. The likely cosecretion of intestinal ghrelin and motilin suggests concerted actions of the two hormones. These data may have implications for understanding gut motility and clinical implications for dysmotility and bariatric surgery.

Not insulin but insulin sensitivity, leptin, and cortisol are major factors regulating serum acylated ghrelin level in healthy women

It has been suggested that insulin and glucose are the most important factors for ghrelin secretion. Most of these studies were performed using total ghrelin assays, detecting two forms of ghrelin (acylated and desacyl), derived from the same peptide precursor but having different biological effects. This study was therefore designed to characterize associations between serum acylated ghrelin levels (Ghr), selected adipocytokines, hormones, and carbohydrate metabolism parameters in healthy women in stable energy metabolism. The study was performed on 32 healthy, normal-weight, non-pregnant women with normal [body mass index (BMI) 18.9-24.2 kg/m2] and stable (the difference between two measurements performed within 1 month being less than 0.5 kg) body weight, aged 22-47 yr. Leptin, Ghr, GH, IGF-I, cortisol, insulin, and glucose were measured in the early follicular phase of the menstruation cycle. Insulin sensitivity was measured using quantitative insulin sensitivity check index (QUICKI). Body composition was assessed by bioimpedance. We found a positive linear correlation between leptin and Ghr (r=0.375; p=0.034) and negative correlation between insulin and Ghr (r=-0.374; p=0.034). GH, IGF-I, adiponectin, and body composition parameters did not correlate with Ghr. In multiple regression analysis only QUICKI, leptin, glucose, and cortisol (positively) and age (negatively) accounted for 50% variation of Ghr. Insulin and BMI did not contribute significantly to the model. Our results suggest that in healthy women basal Ghr level is regulated by multiple factors, mainly by insulin sensitivity, leptin, and adrenal glands activity. However, further studies are needed to elucidate the physiological mechanisms involved in acylated Ghr secretion.

Active immunization against ghrelin decreases weight gain and alters plasma concentrations of growth hormone in growing pigs

Ghrelin has been implicated in the control of food intake and in the long-term regulation of body weight. We theorize that preventing the ability of ghrelin to interact with its receptors, would eventually lead to decreased appetite and thereby decrease body weight gain. To test our hypothesis, pigs were actively immunized against ghrelin. Ghrelin((1-10)) was conjugated to BSA and emulsified in Freund's incomplete adjuvant and diethylaminoethyl-dextran. Primary immunization was given at 19 weeks of age (WOA), with booster immunizations given 20 and 40 days after primary immunization. Body weight (BW) and plasma samples were collected weekly beginning at 19 WOA, and feed intake was measured daily. Fourteen days after primary immunization, the percentage of bound (125)I-ghrelin in plasma from immunized pigs was increased compared with control animals (P<0.001). Voluntary feed intake was decreased more than 15% in animals that were actively immunized against ghrelin compared with controls. By the end of the experiment, immunized pigs weighed 10% less than control animals (P<0.1). Concentrations of GH were increased (P<0.05) in immunized pigs. Apoptosis was not observed in post-mortem samples obtained from the fundic region of the stomach. Our observations suggest that immunization against ghrelin induces mild anorexia. This procedure could potentially be used as a treatment to control caloric intake and obesity.

Ghrelin ligand-receptor mRNA expression in hypothalamus, proventriculus and liver of chicken (Gallus gallus domesticus): Studies on ontogeny and feeding condition

We report here the ontogenic changes in mRNA expression of chicken ghrelin (cGhrelin) and its receptor (cGHS-R1a) and the effects of fasting and refeeding on cGhrelin and cGHS-R1a mRNAs expression in 30-day-old broiler chickens. The level of cGhrelin mRNA in the proventriculus was low from embryo--day 15 (E15) to E19, but dramatically increased at post-hatching-day 2 (P2), then remained constant until P30 and followed by a significant decrease at P44 when there was a diet transition at P31 and thereafter. The decreased level was reversed at P58. Hypothalamic cGhrelin mRNA and proventriculus and hepatic cGHS-R1a mRNA were significantly increased at P30. The cGhrelin mRNA level in the proventriculus significantly increased in response to either 12-h or 36-h fasting but did not decrease after subsequent 12-h refeeding. The level of cGHS-R1a mRNA in the proventriculus was significantly upregulated in response to a 12-h fast but not to a 36-h fast and returned to the control level upon 12-h refeeding. Interestingly, it was apparent that the mRNA levels of both cGhrelin and cGHS-R1a in the liver were upregulated in response to fasting in a time-dependent manner and returned to the control level with subsequent refeeding. These results suggest that the expression pattern of ghrelin and its receptor mRNAs distinctly change in tissues depending on ontogenic stages and feeding states in poultry.

Endogenous acyl ghrelin is involved in mediating spontaneous phase III-like contractions of the rat stomach

In humans and dogs, it is known that motilin regulates phase III contractions of migrating motor complex (MMC) in the fasted state. In rats, however, motilin and its receptor have not been found, and administration of motilin failed to induce any phase III-like contractions. Ghrelin was discovered as the endogenous ligand for the growth hormone secretagogue receptor (GHS-R) from the rat stomach. Ghrelin promotes gastric premature phase III (phase III-like contractions) in the fasted state in rats. We hypothesized that endogenous ghrelin regulates spontaneous phase III-like contractions in rats. Strain gauge transducer was sutured on the antrum and a catheter was inserted into the jugular vein. We studied the effects of i.v. administration of ghrelin and a GHS-R antagonist on gastric phase III-like contractions in conscious rats. Plasma level of ghrelin was measured by a radioimmunoassay. Ghrelin augmented spontaneous phase III-like contractions and a GHS-R antagonist significantly attenuated the occurrence of spontaneous phase III-like contractions. During the phase I period, plasma ghrelin level increased to its peak then returned to basal level, subsequently phase III-like contractions were observed. These results suggest that endogenous ghrelin regulates gastric phase III-like contractions in rats.

The autonomic nervous system regulates gastric ghrelin secretion in rats

Plasma ghrelin levels are responsive to short- and long-term nutrient fluctuation, but the mechanisms of its regulation are largely unknown. To explore the role of the autonomic nervous system in the regulation of ghrelin secretion, we measured plasma ghrelin levels after administration of cholinergic and adrenergic agents in rats under normally fed and 48-h fasting conditions. To assess the short- and long-term effects of vagotomy on ghrelin secretion, plasma ghrelin levels and stomach ghrelin levels and gene expressions were measured in rats subjected to fed or fasting. Additionally, we investigated whether plasma ghrelin levels were affected by the anorexigenic gastrointestinal peptides cholecystokinin and somatostatin. In the pharmacological study, plasma ghrelin levels were increased by a muscarinic agonist, an alpha-adrenergic antagonist, and a beta-adrenergic agonist, and decreased by a muscarinic antagonist and an alpha-adrenergic agonist. Vagotomy inhibited ghrelin secretion acutely, but promoted ghrelin release from the stomach at later time points. Stomach ghrelin mRNA levels were unchanged after fasting, but were significantly upregulated in vagotomized rats. The change of plasma ghrelin levels in nutrient fluctuation was independent of the endogenous effects of cholecystokinin and somatostatin. This study demonstrates that stomach ghrelin secretion is modulated by both the cholinergic and adrenergic arms of the autonomic nervous system. The dissociation between the short- and long-term effects of vagotomy on plasma ghrelin level indicates that an additional neural control mechanism might be involved in the regulation of ghrelin secretion.

Ghrelin affects gastrectomy-induced decrease in UCP1 and β3-AR mRNA expression in mice

In this study we investigated the effects of gastrectomy (Gx) and of the gastric hormone, ghrelin, on the expression of proteins in brown adipose tissue (BAT) that are thought to be involved in thermogenesis. Heat production in BAT is known to depend upon activation and increased expression of beta3-adrenergic receptors (beta3-AR) and the consequent up-regulation of uncoupling protein 1 (UCP1). Mice were subjected to Gx or sham operation. One week later they started to receive daily subcutaneous injections of either saline or ghrelin (12 nmol) for two or eight weeks. Neither Gx nor ghrelin affected daily food intake. Gx did not lower body weight gain (except during the first post-operative week) but Gx mice responded to eight weeks of ghrelin treatment with a greater body weight increase (37%, p<0.05) than saline-injected Gx mice; sham-operated mice did not respond to ghrelin. Gx resulted in a greatly reduced expression of both UCP1 and beta3-AR mRNA in BAT (50% reduction or more, p<0.01) compared to sham-operated mice. Eight weeks of ghrelin treatment raised the UCP1 as well as the beta3-AR mRNA expression in the Gx mice, whereas two weeks of ghrelin treatment decreased UCP1 and beta3-AR mRNA expression compared to Gx mice receiving saline. In fact, mRNA expression in Gx mice after treatment with ghrelin for eight weeks was similar to that in saline-treated sham-operated mice. Ghrelin did not affect UCP1 and beta3-AR mRNA in sham-operated mice neither two nor eight weeks after the operation. The results suggest 1) that signals from the stomach stimulate BAT UCP1 (and possibly thermogenesis) and 2) that ghrelin may contribute to the control of UCP1 expression.

Intraventricular ghrelin activates oxytocin neurons: implications in feeding behavior

Ghrelin affects behavioral and physiological responses, such as feeding or the activity of the HPA axis. Distribution of its receptor in central sites involved in neuroendocrine control, including the hypothalamic paraventricular nucleus, indicates that interplay with multiple neuropeptidergic systems underlies ghrelin's actions. We report that intracerebroventricular ghrelin increases c-Fos immunoreactivity of oxytocin neurons in magno and parvocellular portions of the paraventricular nucleus. The orexigenic response to ghrelin administered at the dose that activates oxytocin neurons can be further elevated by pretreatment with a selective oxytocin receptor antagonist. Our data suggest that oxytocin may be responsible for the mediation of some effects induced by ghrelin. Modifications in the activity of the oxytocin system may alter some of these effects.

Secretion of ghrelin from rat stomach ghrelin cells in response to local microinfusion of candidate messenger compounds: a microdialysis study

Ghrelin is produced by A-like cells (ghrelin cells) in the mucosa of the acid-producing part of the stomach. The mobilization of ghrelin is stimulated by nutritional deficiency and suppressed by nutritional abundance. In an attempt to identify neurotransmitters and regulatory peptides that may contribute to the physiological, nutrient-related regulation of ghrelin secretion, we challenged the ghrelin cells in situ with a wide variety of candidate messengers, including known neurotransmitters (e.g. acetylcholine, catecholamines), candidate neurotransmitters (e.g. neuropeptides), local tissue hormones (e.g. serotonin, histamine, bradykinin, endothelin), circulating gut hormones (e.g. gastrin, CCK, GIP, neurotensin, PYY, secretin) and other circulating hormones/regulatory peptides (e.g. calcitonin, glucagon, insulin, PTH). Microdialysis probes were placed in the submucosa of the acid-producing part of the rat stomach. Three days later, the putative messenger compounds were administered via the microdialysis probe (reverse microdialysis) at a screening dose of 0.1 mmol l(-1) for regulatory peptides and 0.1 and 1 mmol l(-1) for amines and amino acids. The rats were awake during the experiments. The resulting microdialysate ghrelin concentration was monitored continuously for 3 h (radioimmunoassay), thereby revealing stimulators or inhibitors of ghrelin secretion. Dose-response curves were constructed for each candidate messenger that significantly (p<0.05) affected ghrelin mobilization at the screening dose. Peptides that showed a (non-significant) tendency to affect ghrelin release at the screening dose were also given at a dose of 0.3 or 1 mmol l(-1). Adrenaline, noradrenaline, endothelin and secretin stimulated ghrelin release, while somatostatin and GRP inhibited. Whether these agents act directly or indirectly on the ghrelin cells remains to be investigated. All other candidate messengers were without measurable effects, including acetylcholine, serotonin, histamine, GABA, aspartic acid, glutamic acid, glycine, VIP, PACAP, CGRP, substance P, NPY, PYY, PP, gastrin, CCK, GIP, insulin, glucagon, GLP and glucose.

Elevated serum ghrelin exerts an orexigenic effect that may maintain body mass index in patients with metastatic neuroendocrine tumors

Ghrelin is a potent orexigenic peptide principally produced in the stomach by a distinct population of neuroendocrine cells in the oxyntic mucosa of the fundus. Exogenous ghrelin given as an intravenous infusion has been shown to increase caloric intake in patients with cancer cachexia. In this study, we hypothesized that elevated endogenous ghrelin, produced by increased neuroendocrine cell tumor burden, also exerts an orexigenic effect helping to maintain body mass index. To evaluate the effect of elevated endogenous ghrelin, 35 patients with neuroendocrine tumors were enrolled, assigning them to one of two groups depending on the presence of hepatic metastases. Following an overnight fast, serum was collected and sent for ghrelin measurement by an outside laboratory. The two groups were well matched for all other relevant clinical variables including subtype of tumor, primary location of tumor and tumor treatment history. Nearly all patients with hepatic metastases had elevated levels of ghrelin compared to the standard reference range given for matched controls. The presence of hepatic metastases was associated with significantly elevated ghrelin levels (p<0.05) and a greater mean body mass index. In addition, we report a positive correlation between serum ghrelin and total tumor surface area and between serum ghrelin and body mass index, suggesting that elevated endogenous ghrelin may be sufficient to overcome any partial ghrelin resistance typically seen in cancer cachexia. These results support the possibility that ghrelin is co-released from neuroendocrine tumors and exerts an orexigenic effect in these patients, helping to maintain their body mass index despite widely disseminated disease.

Central ghrelin induces feeding driven by energy needs not by reward

Centrally administered ghrelin, the endogenous agonist of the growth hormone secretegogue receptor, powerfully stimulates food intake. Although the orexigenic action of this peptide has been well established, it remains unclear whether ghrelin-induced hyperphagia is driven by energy needs or by reward. In our study ghrelin was injected into the lateral cerebral ventricle or the hypothalamic paraventricular nucleus of rats given a choice between a palatable yet calorie-dilute sucrose solution and a calorically dense chow. As a result of intraventricular and hypothalamic paraventricular ghrelin injections, animals increased intake of chow but not sucrose. When the sucrose solution was offered as the only source of calories, rats treated with ghrelin infused in the ventricle and site-specifically increased sucrose consumption. These results suggest that the primary effect of ghrelin is to stimulate food intake to satisfy energy needs.

Role of ghrelin and leptin in predicting the severity of acute pancreatitis

Ghrelin and leptin are the hormones that influence endocrine and exocrine functions of the pancreas and regulate feeding behaviors and energy metabolism. The aim of this study was to investigate the levels of ghrelin and leptin in pancreatitis of different severities and the relation of these hormones with blood glucose level and proinflammatory cytokines. The study was performed on 90 Wistar Albino rats. Three experimental groups composed of 30 rats were established: control group, 0.9% NaCl solution was injected intraperitoneally (i.p); acute edematous pancreatitis (AEP) group, 1 microg/100 g cerulein was injected i.p. five times, at 1-hr intervals; and acute necrotizing pancreatitis (ANP) group, 500 mg/100 g L-arginine was injected i.p. Ten animals in each group were sacrificed under anesthesia 12, 24 and 48 hr after the last injection. After blood withdrawal, the pancreas was totally excised. The levels of blood sugar, lipase, serum tumor necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta), ghrelin, and leptin were investigated and histopathologic examination was performed. Following pancreatitis induction, serum ghrelin levels increased at 24 hr and reached the peak level at 48 hr. Its level in the AEP group was higher than in the ANP group. Serum leptin levels in the AEP and ANP groups increased after 12 hr and stayed at high levels until 48 hr compared with the control group. Similarly to ghrelin and leptin, blood glucose levels increased in both pancreatitis groups, but the increase was more prominent in the ANP group, with levels >200 mg/ml at 48 hr. The levels of TNF-alpha and IL-1beta in the AEP and ANP groups reached the peak level at 24 hr and then decreased to a level close to that of the control group at 48 hr. We conclude that serum leptin and ghrelin levels increase in the first 48 hr of AEP and ANP. As the serum ghrelin levels in ANP are higher than in AEP, it can be used as a marker to show the severity of pancreatitis. While TNF-alpha and IL-1beta can be used as a prognostic factor in the first 24 hr, ghrelin and leptin can be used subsequently.