Ontogeny of ghrelin mRNA expression and identification of ghrelin-immunopositive cells in the gastrointestinal tract of the Peking duck, Anas platyrhynchos

Ghrelin regulates sepsis‑induced rat acute gastric injury

Ghrelin, a peptide expressed in the gastric mucosa, has an essential role in sustaining the normal function of the digestive system. Sepsis is one of the primary causes of mortality in intensive care units and can lead to multiple organ dysfunction, especially in the gastrointestinal system. The aim of the present study was to explore the effect of ghrelin on gastric blood flow in a rat model of sepsis, as well as the effect of ghrelin on the expression of the apoptotic markers, B-cell lymphoma 2 (Bcl-2) and Bcl-2-associated X (Bax), in gastric tissues. The sepsis model was established using cecal ligation and puncture (CLP). The expression levels of apoptosis-related factors in gastric epithelial cell were determined by immunohistochemistry, reverse transcription quantitative-PCR and western blotting. Collectively, the present results suggested that ghrelin administration attenuated sepsis symptoms induced by CLP. Blood flow in the stomach greater curvature was significantly higher in the CLP-induced sepsis group rats (284.3±95.7 perfusion units) compared with the sham operation group (317.8±5.2 perfusion units; P<0.05), whereas there was no difference between the CLP group treated with ghrelin (377.8±99.0 perfusion units) and the sham rats. Ghrelin administration also reduced the secretion of pro-inflammatory cytokines compared with the CLP-induced sepsis group rats. In addition, CLP significantly reduced the expression of Bcl-2 and enhanced the expression of the pro-apoptotic proteins, Bax and cleaved caspase-3; whereas, ghrelin application reversed the effects of CLP on these apoptosis-associated proteins. In conclusion, the present study revealed that ghrelin has the ability to increase blood flow in the gastrointestinal tract in a sepsis model and can also regulate the expressions of apoptosis-associated factors in gastric tissues. These results suggest that ghrelin could be a novel treatment for sepsis-induced gastric injury.

Immunohistochemical Characterization of PepT1 and Ghrelin in Gastrointestinal Tract of Zebrafish: Effects of Spirulina Vegetarian Diet on the Neuroendocrine System Cells After Alimentary Stress

Gastrointestinal function in vertebrates is influenced by stressors, such as fasting and refeeding, different types of diet and hormonal factors. The aim of this paper was to analyze the effect of a Spirulina (Arthrospira platensis) diet, a microalga known for its nutraceutical properties, on the gastrointestinal tract of zebrafish (Danio rerio) regarding expression of oligopeptide transporter 1 (PepT1) and ghrelin (GHR). Food deprivation and refeeding was investigated to elucidate expression of PepT1 and GHR at a gastrointestinal level and the zebrafish compensatory mechanism. PepT1 is responsible for absorbing di- and tripeptides through a brush border membrane of intestinal mucosa. GHR is a brain-gut peptide in fish and mammals, stimulating growth hormone secretion and regulating appetite. Samples were taken after 2 and 5 days of specimen fasting, and 2 and 5 days of refeeding with Sera Spirulina tabs, in which the major constituent is Spirulina sp. (50.2% protein). Morphological and immunohistochemical analysis of PepT1 and GHR were carried out. Control specimen intestinal tract showed normal morphology of the digestive tract. Fasting caused fold structural changes and intestinal lumen constriction. Immunohistochemical analysis showed a PepT1 level reduction after fasting and an increase after refeeding, reaching very high levels after 5 days, compared to controls. GHR levels increased after food deprivation and gradually decreased after refeeding. Increased expression of PepT1 in refeeding fish suggests a compensatory physiological mechanism, as does the increase in GHR levels in fasting fish followed by a reduction after refeeding. A compensatory mechanism may be induced by fasting and refeeding and by a higher protein Spirulina diet. The microalga, for its nutraceutical properties, is an excellent candidate for animal breeding and human diet.

Distribution and morphology of ghrelin immunostained cells in the adrenal gland of the African ostrich

Ghrelin is the endogenous ligand for the growth hormone secretagogue receptor. We investigated the distribution and morphological characteristics of ghrelin-immunopositive (ghrelin-ip) cells in the African ostrich adrenal gland. We found that the adrenal gland of the African ostrich consisted of three parts: capsule, inter-renal tissue and chromaffin cells. The inter-renal tissue and chromaffin cells interdigitated irregularly. The inter-renal tissue consisted of a peripheral zone and a central inner zone. The peripheral zone could be divided into an outer subcapsular zone and an inner zone. The subcapsular zone cells were arranged as a bow, while the inner area cells formed cords that were perpendicular to the capsule. The central inner zone exhibited irregular clumps and the cells were morphologically similar to chromaffin cells. Ghrelin-ip cells were located throughout the adrenal gland except the capsule. The majority of ghrelin-ip cells were found among the chromaffin cells. The number of ghrelin-ip cells in the inter-renal tissue decreased gradually from the central inner zone, to the inner zone to the subcapsular zone. The ghrelin-ip cells were oval or irregular in shape and exhibited cytoplasmic staining. Our findings suggest that ghrelin may play a role in regulating adrenal hormone secretion in the African ostrich.

Gut Hormones and Regulation of Food Intake in Birds

Gut hormones act as appetite regulatory hormones in mammals. For example, the hunger hormone ghrelin, which is released from the stomach before food intake, stimulates appetite. In contrast, satiety hormones such as cholecystokinin, glucagon-like peptide-1, and peptide YY, which are released from the intestines after food intake, suppress appetite. The effects of these peptides on food intake have been shown to be similar in both mammals and fishes. However, evidence suggests that the physiological roles of these gut hormones may be different between birds and other vertebrates. This review summarizes the current information on the roles of gut hormones in the regulation of food intake in birds, especially in chickens.

Molecular cloning, characterization, and expression analysis of ghrelin and cholecystokinin in the pigeon (Columba livia)

Ghrelin and cholecystokinin (CCK) are multifunctional peptides. In the current study, complete sequences of ghrelin (800 bp) and CCK (739 bp) were firstly cloned in Columba livia by using rapid amplification of cDNA ends (RACE) method. The open reading frames of ghrelin (351bp) and CCK (393bp) encoded 116 amino acids and 130 amino acids, respectively. Sequence comparison indicated that pigeon ghrelin and CCK shared high identity with those reported in other avian species. Quantitative real-time PCR analysis found that ghrelin and CCK mRNAs expressed in three intestinal segments of pigeon during development. Both ghrelin and CCK showed generally higher expressions at days posthatch than embryonic periods regardless of intestinal segments. In duodenum and ileum, the expressions of ghrelin and CCK mRNA reached the peak values at 8 d posthatch. Jejunum CCK mRNA level increased linearly after hatching, and reached the highest point at posthatch 28 d. Based on documented effects of long chain fatty acids (LCFAs) on pigeon ghrelin and CCK expression were also investigated in vitro. Higher concentrations (50 μM or 250 μM) of linoleic acid, α-linolenic acid or arachidonic acid can significantly increase ghrelin mRNA level in pigeon jejunum. However, for oleic acid, the induction of ghrelin gene expressions needed a lower concentration (5 μM). 5 μM of linoleic acid, α-linolenic acid or arachidonic acid and 250 μM palmitic acid repressed CCK expression significantly. A higher concentration (250 μM) of oleic acid or α-linolenic acid can up-regulate CCK mRNA level significantly. Our results indicated that ghrelin and CCK may act key functions in pigeon intestine development and their expressions could be regulated by LCFAs.

Localization of ghrelin-like peptide in the gastrointestinal tract of the golden apple snail (Pomacea canaliculata) and changing of its concentration during fasting

Ghrelin is an endogenous hormone detected in the gastrointestinal tracts (GI) of various species. In the present study, ghrelin-like peptide (ghrelin-LP) was identified in the GI tract of the golden apple snail, Pomacea canaliculata. Using immunohistochemistry, the result revealed an immunoreactivity (-ir) of ghrelin-LP in regions of the GI tract. The ghrelin-LP-ir was observed in both opened-type and closed-type cells of the esophagus, stomach, and small and large intestines. The highest density of ghrelin-LP immunoreactive cells was found in the esophagus and the least density was detected in the stomach. The highest percentages of the opened-type and closed-type cells were present in the esophagus and small intestine, respectively. In immunoblotting, the molecular weight of ghrelin-LP was related to the human ghrelin peptide (∼13kDa). Moreover, the concentration of ghrelin-LP was significantly higher in snails that were fasted for 24h compared with fed snails. The concentration decreased after refeeding. The present study could be useful for understanding the physiological role of ghrelin-LP in mollusk species.

Correlation of ghrelin concentration and ghrelin, ghrelin-O-acetyltransferase (GOAT) and growth hormone secretagogue receptor 1a mRNAs expression in the proventriculus and brain of the growing chicken

To determine mechanisms for age-related decrease of GHS-R1a expression in the chicken proventriculus, changes in mRNA expression of ghrelin and ghrelin-O-acetyltransferase (GOAT) as well as ghrelin concentrations in the proventriculus and plasma were examined in growing chickens. Changes in expression levels of ghrelin, GOAT and GHS-R1a mRNAs were also examined in different brain regions (pituitary, hypothalamus, thalamus, cerebellum, cerebral cortex, olfactory bulb, midbrain and medulla oblongata). Ghrelin concentrations in the proventriculus and plasma increased with aging and reached plateaus at 30-50 days after hatching. High level of ghrelin mRNA decreased at 3 days after hatching, and it became stable at half of the initial level. Expression levels of GHS-R1a and GOAT decreased 3 or 5 days after hatching and became stable at low levels. Significant negative correlations were found between plasma ghrelin and mRNA levels of GOAT and GHS-R1a. Expression levels of ghrelin mRNA were different in the brain regions, but a significant change was not seen with aging. GHS-R1a expression was detected in all brain regions, and age-dependent changes were observed in the pituitary and cerebellum. Different from the proventriculus, the expression of GOAT in the brain increased or did not change with aging. These results suggest that decreased GHS-R1a and GOAT mRNA expression in the proventriculus is due to endogenous ghrelin-induced down-regulation. Expression levels of ghrelin, GOAT and GHS-R1a in the brain were independently regulated from that in the proventriculus, and age-related and region-dependent regulation pattern suggests a local effect of ghrelin system in chicken brain.

Recent advances in the phylogenetic study of ghrelin

To understand fully the biology of ghrelin, it is important to know the evolutionary history of ghrelin and its receptor. Phylogenetic and comparative genomic studies of mammalian and non-mammalian vertebrates are a useful approach to that end. Ghrelin is a hormone that has apparently evaded natural selection during a long evolutionary history. Surely ghrelin plays crucial physiological roles in living animals. Phylogenetic studies reveal the nature and evolutionary history of this important signaling system.