Ghrelin, an acylated brain and gut peptide, is primarily produced by endocrine cells of the gastric mucosa for secretion into the circulation. The major active form of ghrelin is a 28-amino-acid ...peptide containing an n-octanoyl modification at serine that is essential for activity. Studies have identified multiple physiological functions for ghrelin, including GH release, appetite stimulation, and metabolic fuel preference. Until now, there has not been any report detailing the mechanism of ghrelin acyl modification. Here we report that ingestion of either medium-chain fatty acids (MCFAs) or medium-chain triacylglycerols (MCTs) increased the stomach concentrations of acylated ghrelin without changing the total (acyl- and des-acyl-) ghrelin amounts. After ingestion of either MCFAs or MCTs, the carbon chain lengths of the acyl groups attached to nascent ghrelin molecules corresponded to that of the ingested MCFAs or MCTs. Ghrelin peptides modified with n-butyryl or n-palmitoyl groups, however, could not be detected after ingestion of the corresponding short-chain or long-chain fatty acids, respectively. Moreover, n-heptanoyl ghrelin, an unnatural form of ghrelin, could be detected in the stomach of mice after ingestion of either n-heptanoic acid or glyceryl triheptanoate. These findings indicate that ingested medium-chain fatty acids are directly used for the acylation of ghrelin.
Ghrelin, an endogenous ligand for the GH secretagogue receptor, was
isolated from rat stomach and is involved in a novel system for
regulating GH release. Although previous studies in rodents suggest
...that ghrelin is also involved in energy homeostasis and that ghrelin
secretion is influenced by feeding, little is known about plasma
ghrelin in humans. To address this issue, we studied plasma
ghrelin-like immunoreactivity levels and elucidated the source of
circulating ghrelin and the effects of feeding state on plasma
ghrelin-like immunoreactivity levels in humans. The plasma ghrelin-like
immunoreactivity concentration in normal humans measured by a specific
RIA was 166.0 ± 10.1 fmol/ml. Northern blot analysis of various
human tissues identified ghrelin mRNA found most abundantly in the
stomach and plasma ghrelin-like immunoreactivity levels in totally
gastrectomized patients were reduced to 35% of those in normal
controls. Plasma ghrelin-like immunoreactivity levels were increased by
31% after 12-h fasting and reduced by 22% immediately after
habitual feeding. In patients with anorexia nervosa, plasma
ghrelin-like immunoreactivity levels were markedly elevated compared
with those in normal controls (401.2 ± 58.4 vs.
192.8 ± 19.4 fmol/ml) and were negatively correlated with body
mass indexes. We conclude that the stomach is a major source of
circulating ghrelin and that plasma ghrelin-like immunoreactivity
levels reflect acute and chronic feeding states in humans.
Ghrelin, a novel growth-hormone-releasing peptide, was discovered in rat and human stomach tissues. However, its physiological and pharmacological actions in the gastric function remain to be ...determined. Therefore, we studied the effects of rat ghrelin on gastric functions in urethane-anesthetized rats. Intravenous administrations of rat ghrelin at 0.8 to 20 μg/kg dose-dependently increased not only gastric acid secretion measured by a lumen-perfused method, but also gastric motility measured by a miniature balloon method. The maximum response in gastric acid secretion was almost equipotent to that of histamine (3 mg/kg, i.v.). Moreover, these actions were abolished by pretreatment with either atropine (1 mg/kg, s.c.) or bilateral cervical vagotomy, but not by a histamine H2-receptor antagonist (famotidine, 1 mg/kg, s.c.). These results taken together suggest that ghrelin may play a physiological role in the vagal control of gastric function in rats.
Ghrelin, an endogenous ligand for the GH secretagogue receptor, is a hormone expressed in stomach and other tissues, such as hypothalamus, testis, and placenta. This hormone acts at a central level ...to stimulate GH secretion and food intake. Little is known, however, about the molecular forms and physiological roles of ghrelin within the hypothalamus. In this report, we detail the molecular forms, mRNA expression patterns, and peptide contents of ghrelin within the rat hypothalamus. Using the combination of reverse-phase HPLC and ghrelin-specific RIA, we determined that the rat hypothalamus contains both n-octanoyl-modified and des-acyl ghrelins. Fasting for 24 and 48 h significantly decreased ghrelin mRNA expression in the hypothalamus to 24% and 28% of control values, respectively. Both n-octanoyl-modified and des-acyl ghrelin content in the hypothalamus decreased after 24 and 48 h of fasting. These results contrast the changes in gastric ghrelin after fasting, which decreased in content despite increased mRNA expression. Two hours after injection of 2-deoxy-d-glucose (2-DG), a selective blocker of carbohydrate metabolism, ghrelin peptide levels also decreased. Thus, induction of glucoprivic states, such as fasting and 2-DG treatment, decreased ghrelin gene expression and peptide content within the hypothalamus.
Ghrelin Is Present in Pancreatic α-Cells of Humans and Rats and Stimulates Insulin Secretion
Yukari Date 1 2 ,
Masamitsu Nakazato 1 ,
Suzuko Hashiguchi 3 4 ,
Katsuya Dezaki 3 ,
Muhtashan S. Mondal 1 ...,
Hiroshi Hosoda 2 ,
Masayasu Kojima 2 ,
Kenji Kangawa 2 ,
Terukatsu Arima 4 ,
Hisayuki Matsuo 2 ,
Toshihiko Yada 3 and
Shigeru Matsukura 1
1 Department of Internal Medicine, Miyazaki Medical College, Miyazaki, Japan
2 National Cardiovascular Center Research Institute, Osaka, Japan
3 Department of Physiology, Jichi Medical School, Tochigi, Japan
4 Second Department of Internal Medicine, Faculty of Medicine, Kagoshima University, Kagoshima, Japan
Abstract
Ghrelin, a novel growth hormone–releasing peptide isolated from human and rat stomach, is a 28–amino acid peptide with a posttranslational
acylation modification that is indispensable for stimulating growth hormone secretion by increasing intracellular Ca 2+ concentration. It also functions in the regulation of feeding behavior, energy metabolism, and gastric acid secretion and
motility. Using two different antibodies against the NH 2 - and COOH-terminal regions of ghrelin, we studied its localization in human and rat pancreas by immunohistochemistry. Ghrelin-immunoreactive
cells were identified at the periphery of pancreatic islets in both species. Ghrelin co-localized exclusively with glucagon
in rat islets, indicating that it is produced in α-cells. We identified ghrelin and des-acyl ghrelin in the rat pancreas using
reverse-phase high-performance liquid chromatography combined with two radioimmunoassays. We also detected mRNA encoding ghrelin
and its receptor in the rat pancreatic islets. Ghrelin increased the cytosolic free Ca 2+ concentration in β-cells and stimulated insulin secretion when it was added to isolated rat pancreatic islets. These findings
indicate that ghrelin may regulate islet function in an endocrine and/or paracrine manner.
Footnotes
Address correspondence and reprint requests to Masamitsu Nakazato, PhD, Third Department of Internal Medicine, Miyazaki Medical
College, Kiyotake, Miyazaki 889-1692, Japan. E-mail: nakazato{at}post.miyazaki-med.ac.jp .
Received for publication 8 August 2001 and accepted in revised form 3 October 2001.
Ca 2+ i , cytosolic free Ca 2+ concentration; GH, growth hormone; GHS, growth-hormone secretagogue; GHS-R, GHS receptor; ICV, intracerebroventricularly;
IV, intravenously; KRB, Krebs-Ringer bicarbonate buffer; PBS, phosphate-buffered saline; RIA, radioimmunoassay; RP-HPLC, reverse-phase
high-performance liquid chromatography; RT-PCR, reverse transcription–polymerase chain reaction; TFA, trifluoroacetic acid.
Ghrelin is a recently identified endogenous ligand for the GH
secretagogue receptor and is involved in a novel system for regulating
GH release. However, little is known about its GH-releasing ...activity
and other endocrine effects in humans. To address this issue, we
studied the GH, ACTH, cortisol, PRL, LH, FSH, and TSH responses to
synthetic human ghrelin. In four normal male adults (28–37 yr), iv
ghrelin administration released GH in a dose-dependent manner and 0.2,
1.0, and 5.0 μg/kg ghrelin produced 43.3 ± 6.0, 81.5 ± 12.7, and
107.0 ± 10.7 ng/mL of the GH peak values at 30 min, respectively.
ACTH, cortisol, and PRL levels were also elevated after ghrelin
injection, while the lowest dose (0.2 μg/kg) resulted in only minimum
peak values of these hormones (22.8 ± 3.0 pg/mL, 9.4 ± 1.9 μg/dL,
and 4.6 ± 0.6 ng/mL, respectively). There were no significant changes
in LH, FSH, or TSH levels. This is the first study showing evidence
that ghrelin strongly stimulates GH release in humans.
1 Division of Endocrinology and Metabolism, Department of Medicine, Kurume University School of Medicine; and 2 Department of Molecular Genetics, Institute of Life Science, Kurume University, Kurume, ...Fukuoka, Japan
Submitted 26 November 2006
; accepted in final form 14 March 2007
Adiponectin, a physiologically active polypeptide secreted by adipocytes, shows insulin-sensitizing, anti-inflammatory, and antiatherogenic properties in rodents and humans. To assess the effects of chronic hyperadiponectinemia on metabolic phenotypes, we established three lines of transgenic mice expressing human adiponectin in the liver. When maintained on a high-fat/high-sucrose diet, mice of two lines that had persistent hyperadiponectinemia exhibited significantly decreased weight gain associated with less fat accumulation and smaller adipocytes in both visceral and subcutaneous adipose tissues. Macrophage infiltration in adipose tissue was markedly suppressed in the transgenic mice. Expression levels of adiponectin receptors were not altered in skeletal muscle or liver. Circulating levels of endogenous adiponectin were elevated, whereas fasting glucose, insulin, and leptin levels were reduced compared with control mice. In the hyperadiponectinemic mice daily food intake was not altered, but oxygen consumption was significantly greater, suggesting increased energy expenditure. Moreover, high-calorie diet-induced premature death was almost completely prevented in the hyperadiponectinemic mice in association with attenuated oxidative DNA damage. The transgenic mice also showed longer life span on a conventional low-fat chow. In conclusion, transgenic expression of human adiponectin blocked the excessive fat accumulation and reduced the morbidity and mortality in mice fed a high-calorie diet. These observations may provide new insights into the prevention and therapy of metabolic syndrome in humans.
adipocyte; macrophage; life span; 8-hyroxy-2-deoxyguanosine
Address for reprint requests and other correspondence: K. Yamada, Dept. of Medicine, Kurume University School of Medicine, 67 Asahimachi, Kurume, Fukuoka 830-0011, Japan (e-mail: yamada{at}med.kurume-u.ac.jp )
Ghrelin is a novel gut–brain peptide that binds to the growth hormone secretagogue receptor (GHS-R), thereby functioning in the regulation of growth hormone (GH) release and food intake. ...Ghrelin-producing cells are most abundant in the oxyntic glands of the stomach. The regulatory mechanism that governs the biosynthesis and secretion of ghrelin has not been clarified. We report that ghrelin mRNA expression in the gastric fundus was increased, but that ghrelin peptide content decreased after a 48-h fast. Both values returned to control levels after refeeding. The ghrelin plasma concentration in the gastric vein and systemic venous blood increased after 24- and 48-h fasts. Furthermore, des-octanoylated ghrelin and n-octanoylated ghrelin were found in rat stomach, with the ratio of des-octanoylated ghrelin to n-octanoylated ghrelin markedly increased after fasting. The ghrelin mRNA level in the stomach also increased after administration of insulin and leptin. Conversely, db/db mice, which are deficient in the leptin receptor, had lower ghrelin mRNA levels than control mice. These findings suggest that this novel gastrointestinal hormone plays a role in the regulation of energy balance.
Ghrelin, an Endogenous Growth Hormone Secretagogue, Is a Novel Orexigenic
Peptide That Antagonizes Leptin Action Through the Activation of Hypothalamic
Neuropeptide Y/Y1 Receptor Pathway
Mitsuyo ...Shintani ,
Yoshihiro Ogawa ,
Ken Ebihara ,
Megumi Aizawa-Abe ,
Fumiko Miyanaga ,
Kazuhiko Takaya ,
Tatsuya Hayashi ,
Gen Inoue ,
Kiminori Hosoda ,
Masayasu Kojima ,
Kenji Kangawa and
Kazuwa Nakao
From the Department of Medicine and Clinical Science (M.S., Y.O., K.E.,
M.A.-A., F.M., K.T., T.H., G.I., K.H., K.N.), Kyoto University Graduate School
of Medicine, Kyoto; and the Department of Biochemistry (M.K., K.K.), National
Cardiovascular Center Research Institute, Osaka, Japan.
Address correspondence and reprint requests to Yoshihiro Ogawa, Department of
Medicine and Clinical Science, Kyoto University Graduate School of Medicine,
54 Shogoin Kawahara-cho, Sakyo-ku, Kyoto 606-8507 Japan. E-mail:
ogawa{at}kuhp.kyoto-u.ac.jp
.
Abstract
Ghrelin, an endogenous ligand for growth hormone secretagogue (GHS)
receptor originally isolated from the stomach, occurs in the hypothalamic
arcuate nucleus and may play a role in energy homeostasis. Synthetic GHSs have
activated the hypothalamic arcuate neurons containing neuropeptide Y (NPY),
suggesting the involvement of NPY in some of ghrelin actions. This study was
designed to elucidate the role of ghrelin in the regulation of food intake. A
single intracerebroventricular (ICV) injection of ghrelin (5-5,000 ng/rat)
caused a significant and dose-related increase in cumulative food intake in
rats. Ghrelin (500 ng/rat) was also effective in growth hormone-deficient
spontaneous dwarf rats. Hypothalamic NPY mRNA expression was increased in rats
that received a single ICV injection of ghrelin (500 ng/rat) (∼ 160% of
that in vehicle-treated groups, P < 0.05). The ghrelin's
orexigenic effect was abolished dose-dependently by ICV co-injection of NPY Y1
receptor antagonist (10-30 μg/rat). The leptin-induced inhibition of food
intake was reversed by ICV co-injection of ghrelin in a dose-dependent manner
(5-500 ng/rat). Leptin reduced hypothalamic NPY mRNA expression by 35%
( P < 0.05), which was abolished by ICV co-injection of ghrelin
(500 ng/rat). This study provides evidence that ghrelin is an orexigenic
peptide that antagonizes leptin action through the activation of hypothalamic
NPY/Y1 receptor pathway.
Footnotes
Posted on the World Wide Web at
www.diabetes.org/diabetes
on <<insert date> 2001.
AGRP, agouti-related protein; GH, growth hormone; GHRH, growth
hormone-releasing hormone; GHS, growth hormone secretagogue; GHS-R, GHS
receptor; ICV, intracerebroventricular; NPY, neuropeptide Y.
Accepted November 9, 2000.
Received August 16, 2000.
by the American Diabetes Association,
Inc.
Departments of 1 Internal Medicine and
2 Biochemistry, National Cardiovascular Center, Osaka
565 - 8565; 3 Department of Internal Medicine, Osaka
Seamen's Insurance Hospital, Osaka 552-0021; and
4 ... Institute for Medical Research and Development, Suntory
Limited, Gunma 370-0503, Japan
To investigate hemodynamic and hormonal effects of
ghrelin, a novel growth hormone (GH)-releasing peptide, we gave six
healthy men an intravenous bolus of human ghrelin (10 µg/kg) or
placebo and vice versa 1-2 wk apart in a randomized fashion.
Ghrelin elicited a marked increase in circulating GH (15-fold). The
elevation of GH lasted longer than 60 min after the bolus injection.
Injection of ghrelin significantly decreased mean arterial pressure
( 12 mmHg, P < 0.05) without a significant change in
heart rate ( 4 beats/min, P = 0.39). Ghrelin significantly
increased cardiac index (+16%, P < 0.05) and stroke
volume index (+22%, P < 0.05). We also examined
ghrelin receptor GH secretagogues receptor (GHS-R) gene expression
in the aortas, the left ventricles, and the left atria of rats by
RT-PCR. GHS-R mRNA was detectable in the rat aortas, left ventricles,
and left atria, suggesting that ghrelin may cause cardiovascular
effects through GH-independent mechanisms. In summary, human
ghrelin elicited a potent, long-lasting GH release and had beneficial
hemodynamic effects via reducing cardiac afterload and increasing
cardiac output without an increase in heart rate.
hemodynamics; hormones; vasodilation
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