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Insulin and Brain Reward Systems
Published in André Kleinridders, Physiological Consequences of Brain Insulin Action, 2023
Brian C. Liu, Qingchen Zhang, Emmanuel N. Pothos
Ghrelin is often known as the “hunger hormone” and is secreted from the stomach (59). The growth hormone secretagogue receptor (GHSR), the receptor for ghrelin, is found in the hypothalamus as well (60, 61). Mice with a GHSR knockout fed with a high-fat diet store fewer calories and have lower body weight and adipose tissue compared to control mice. These mice also demonstrate improved glucose homeostasis. The site of action by which ghrelin increases food intake and adipose tissue appears to be the hypothalamus (62). Indeed, it has been hypothesized that the effects of ghrelin may oppose and regulate the effects of leptin and insulin in the hypothalamus (61). There is additional evidence that ghrelin, like leptin, not only impacts on homeostatic processing of energy balance but also on hedonic properties of food intake and underlying neurotransmission (62–65) so much so that it plays a significant role in the neurochemical ‘signatures” of obesity and eating disorders. Although the synergistic or additive role of central insulin to ghrelin effects on food reward has not been adequately investigated, one can only assume that such interaction is at play and likely constitutes a significant part of the neurochemical phenotype of disorders that impact both metabolism and hedonic/compulsive food intake.
Prader–Willi Syndrome: An Example of Genomic Imprinting
Published in Merlin G. Butler, F. John Meaney, Genetics of Developmental Disabilities, 2019
Recently, ghrelin, an endogenous ligand of the growth hormone secretagogue receptor which is G-protein coupled and located in the hypothalamus, is produced by the stomach (35). It is involved with energy balance and appetite stimulation. Adults and children (including infants during stage one or failure to thrive period) have been reported with fasting ghrelin levels three to five times higher than obese or nonobese control subjects (36–38). Additional testing of this peptide and others (e.g., peptide YY) involved in eating behavior in PWS subjects will be needed to understand their role in the hyperphagia and insatiable appetite seen as cardinal features of PWS.
Central and Peripheral Modulators of Appetite and Satiety
Published in Emmanuel C. Opara, Sam Dagogo-Jack, Nutrition and Diabetes, 2019
Gabrielle Page-Wilson, Sam Dagogo-Jack
The polypeptide ghrelin was initially described and characterized as the endogenous ligand for the growth hormone secretagogue receptor in 1999 (Kojima et al. 1999). The ghrelin molecule contains 28 amino acids and an acyl radical, the latter being essential for biologic effect. The post-translational acylation of ghrelin is mediated by the enzyme gastric O-acyl transferase (GOAT) (Yang et al. 2008). Ghrelin is synthesized and secreted by the stomach, reaches the anterior pituitary via the circulation, and stimulates growth hormone secretion by the somatotrophs. The nutritional effects of ghrelin became evident when it was shown that central (ICV) administration potently increased food intake in rodents (Wren et al. 2000). A similar effect on food intake was observed following peripheral (IV) injection of ghrelin in rats (Wren et al. 2000). In humans, intravenous administration of ghrelin stimulates food intake by approximately 30% (Wren et al. 2001). Interestingly, ghrelin is the only metabotropic peptide thus far identified that stimulates food intake directly when administered peripherally.
An overview of ghrelin O-acyltransferase inhibitors: a literature and patent review for 2010-2019
Published in Expert Opinion on Therapeutic Patents, 2020
Jacob E. Moose, Katelyn A. Leets, Nilamber A. Mate, John D. Chisholm, James L. Hougland
Ghrelin is a 28-amino acid peptide hormone that is notable as the only known hunger-stimulating hormone in humans. Originally discovered in 1999 during the search for the endogenous ligand of the growth hormone secretagogue receptor (GHS-R1a), ghrelin stimulates the release of growth hormone (GH) upon receptor activation [1]. When compared to ghrelin isolated from rat stomach extracts by reverse-phase HPLC, a synthetic ghrelin peptide exhibited a shift in retention time indicating the presence of a hydrophobic modification on the naturally occurring hormone [1]. This modification was identified as octanoylation of the hydroxyl sidechain of serine-3, with this acylation found to be essential for ghrelin to activate GH secretion [1]. While originally identified in the stomach, ghrelin expression has also been reported in a wide range of other tissues, consistent with the variety of physiological effects attributed to ghrelin signaling [1–4].
Hemostatic effect of acylated ghrelin in control and sleeve gastrectomy-induced rats: mechanisms of action
Published in Archives of Physiology and Biochemistry, 2020
Ghrelin is a 28-amino acid gut hormone that is mainly secreted by the stomach cell (and other cells) to increase appetite and energy balance (Ghelardoni et al.2006). Initially, ghrelin has been identified as an endogenous ligand of the orphan receptor growth hormone secretagogue receptor 1a (GHS-R1a) to increase the release of the growth hormone (GH) (Ghelardoni et al.2006). Ghrelin circulates in the blood in two forms, namely, an acylated ghrelin (AG, n-octanoylated at Ser3) and an unacylated ghrelin (UAG) (Zhang and Xiao-Ming 2015). Acylation is achieved by the activation of an enzyme called GOAT (Zhang and Xiao-Ming 2015). Of interest, only AG is able to activate GHS-R1a whereas the UAG has been found to have multiple metabolic functions with unknown receptors (Zhang and Xiao-Ming 2015).
Ghrelin prevents cardiac cell apoptosis during cardiac remodelling post experimentally induced myocardial infarction in rats via activation of Raf-MEK1/2-ERK1/2 signalling
Published in Archives of Physiology and Biochemistry, 2019
Refaat A. Eid, Mahmoud A. Alkhateeb, Mubarak Al-Shraim, Samy M. Eleawa, Abdullah S. Shatoor, Attalla Farag El-Kott, Mohamed Samir Ahmed Zaki, Khalid A. Shatoor, Ismaeel Bin-Jaliah, Fahaid H. Al-Hashem
Ghrelin, a 28-amino-acid hormone peptide is an endogenous ligand of the orphan receptor growth hormone secretagogue receptor 1a (GHS-R1a). Ghrelin is mainly secreted from the mucosa of the stomach, as well as other tissues (Ghelardoni et al. 2006). An indication of the role of ghrelin in the regulation of cardiovascular (CV) function came from a study which reported that human endothelial cells can synthesize ghrelin and that ghrelin receptors can be found in human endothelial cells, vascular smooth muscle cells, and the left ventricle (Kleinz et al. 2006). The beneficial CV effects of ghrelin administration have been shown in animal models of I/R injury, MI, as well as in normal subjects, or those who survived from MI with or without HF, where ghrelin reduced the infarct size and left ventricle (LV) enlargements, enhanced LV contractility, improved cardiac output and index, and attenuated left-ventricular remodelling (Nagaya et al. 2001a, 2001b, 2001c, 2004, Frascarelli et al. 2003). In addition, within the CV system, the anti-apoptotic effect of ghrelin had been noted since ghrelin prevented apoptosis in H9c2 cardiomyocytes and endothelial cells via the activation of ERK1/2 and PI3K/Akt signalling (Baldanzi et al. 2002). However, the effect of ghrelin on ERK1/2 signalling in late stage post-MI remodelling in vivo is not known.