Ghrelin is a new orexigenic peptide primarily produced by the stomach but also present in the hypothalamus. It has adipogenic effects when it is chronically injected in rodents but in obese humans, its plasma concentration is decreased. It can reverse the anorectic effects of leptin when it is co-injected with this peptide in the brain ventricles. The Zucker fa/fa rat is a genetic model of obesity related to a default in the leptin receptor. It is characterized by a large dysregulation of numerous hypothalamic peptides but the ghrelin status of this rat has not yet been determined. Through several experiments, we determine in lean and obese Zucker rats its circulating form in the plasma, its tissue levels and/or expression, and studied the influence of different feeding conditions and its light/dark variations. Ghrelin expression was higher in the obese stomach and hypothalamus (P < 0.05 and P < 0.02, respectively). The ratio of [Octanoyl-Ser3]-ghrelin (active form) to [Des-Octanoyl-Ser3]-ghrelin (inactive form) was approximately 1:1 in the stomach and 2:1 in the plasma in lean and obese rats (no differences). After fasting, plasma ghrelin concentrations increased significantly in lean (+ 64%; P < 0.001) and obese (+ 60%; P < 0.02) rats. After 24 hours of refeeding, they returned to their initial ad lib levels. Ghrelin concentrations were higher in obese rats by 69% (P < 0.005), 65% (P < 0.02), and 73% (P < 0.005) in the ad libitum, fast, and refed states respectively. These results indicate that the obese Zucker rat is characterized by increases in the stomach mRNA expression and in peptide release in the circulation. They clearly support a role for ghrelin in the development of obesity in the absence of leptin signaling.
KojimaM, HosodaH, DateY, NakazatoM, MatsuoH, KangawaK.Ghrelin is a growth-hormone-releasing acylated peptide from stomach. Nature402: 656–660, 1999.
2.
AriyasuH, TakayaK, TagamiT, OgawaY, HosodaK, AkamizuT, SudaM, KohT, NatsuiK, ToyookaS, ShirakamiG, UsuiT, ShimatsuA, DoiK, HosodaH, KojimaM, KangawaK, NakaoK.Stomach is a major source of circulating ghrelin, and feeding state determines plasma ghrelin-like immunoreactivity levels in humans. J Clin Endocrinol Metab86: 4753–4758, 2001.
3.
DateY, KojimaM, HosodaH, SawaguchiA, MondaiMS, SuganumaT, MatsukuraS, KangawaK, NakazatoM.Ghrelin, a novel growth hormone-releasing acylated peptide, is synthesized in a distinct endocrine cell type in the gastrointestinal tracts of rats and humans. Endocrinology141: 4255–4261, 2000.
4.
GuanXM, YuH, PalyhaOC, McKeeKK, FeighnerSD, SirinathsinghjiDJ, SmithRG, Van der PloegLH, HowardAD. Distribution of mRNA encoding the growth hormone secretagogue receptor in brain and peripheral tissues. Mol Brain Res48: 23–29, 1997.
5.
HosodaH, KojimaM, MatsuoH, KangawaK.Ghrelin and des-acyl ghrelin: Two major forms of rat ghrelin peptide in gastrointestinal tissue. Biochem Biophys Res Commun279: 909–913, 2000.
6.
MatsumotoM, HosodaH, KitajimaY, MorozumiN, MinamitakeY, TanakaS, MatsuoH, KojimaM, HayashiY, KangawaK.Structure-activity relationship of ghrelin: Pharmacological study of ghrelin peptides. Biochem Biophys Res Commun287: 142–146, 2001.
7.
BednarekMA, FeighnerSD, PongSS, McKeeKK, HreniukDL, SilvaMV, WarrenVA, HowardAD, VanderPloegLHY, HeckJV. Structure-function studies on the new growth hormone-releasing peptide, ghrelin: Minimal sequence of ghrelin necessary for activation of growth hormone secretagogue receptor la. J Med Chem43: 4370–4376, 2000.
8.
DateY, MurakamiN, KojimaM, KuroiwaT, MatsukuraS, KangawaK, NakazatoM.Central effects of a novel acylated peptide, ghrelin, on growth hormone release in rats. Biochem Biophys Res Commun275: 477–480, 2000.
9.
SeoaneLM, TovarS, BaldelliR, ArvatE, GhigoE, CasanuevaFF, DieguezC.Ghrelin elicits a marked stimulatory effect on GH secretion in freely-moving rats. Eur J Endocrinol143: R7–R9, 2000.
10.
NakazatoM, MurakamiN, DateY, KojimaM, MatsuoH, KangawaK, MatsukuraS.A role for ghrelin in the central regulation of feeding. Nature409: 194–198, 2001.
HorvathTL, DianoS, SotonyiP, HeimanM, TschopM.Minireview: Ghrelin and the regulation of energy balance: A hypothalamic perspective. Endocrinology142: 4163–4169, 2001.
13.
CummingsDE, PurnellJQ, FrayoRS, SchmidovaK, WisseBE, WeigleDS. A preprandial rise in plasma ghrelin levels suggests a role in meal initiation in humans. Diabetes50: 1714–1719, 2001.
14.
Louis-SylvestreJ, LeMagnenJ.A fall in blood glucose level precedes meal onset in free-feeding rats. Neurosci Biobehav Rev4: 13–15, 1980.
15.
TschopM, WawartaR, RieplRL, FriedrichS, BidlingmaierM, LandgrafR, FolwacznyC.Post-prandial decrease of circulating human ghrelin levels. J Endocrinol Invest24: RC19–RC21, 2001.
16.
ToshinaiK, MondaiMS, NakazatoM, DateY, MurakamiN, KojimaM, KangawaK, MatsukuraS.Upregulation of ghrelin expression in the stomach upon fasting, insulin-induced hypoglycemia, and leptin administration. Biochem Biophys Res Commun281: 1220–1225, 2001.
17.
AsakawaA, InuiA, KagaT, YuzurihaH, NagataT, UenoN, MakinoS, FujimiyaM, NiijimaA, FujinoMA, KasugaM.Ghrelin is an appetite-stimulatory signal from stomach with structural resemblance to motilin. Gastroenterology120: 337–345, 2001.
MuccioliG, PapottiM, LocatelliV, GhigoE, DeghenghiR.Binding of I-125-labeled ghrelin to membranes from human hypothalamus and pituitary gland. J Endocrinol Invest24: RC7–RC9, 2001.
21.
HewsonAK, DicksonSL. Systemic administration of ghrelin induces Fos and Egr-1 proteins in the hypothalamic arcuate nucleus of fasted and fed rats. J Neuroendocrinol12: 1047–1049, 2000.
22.
KamegaiJ, TamuraH, ShimizuT, IshiiS, SugiharaH, WakabayashiI.Central effect of ghrelin, an endogenous growth hormone secretagogue, on hypothalamic peptide gene expression. Endocrinology141: 4797–4800, 2000.
23.
KamegaiJ, TamuraH, ShimizuT, IshiiS, SugiharaH, WakabayashiI.Chronic central infusion of ghrelin increases hypothalamic neuropeptide Y and Agouti-related protein mRNA levels and body weight in rats. Diabetes50: 2438–2443, 2001.
24.
ShintaniM, OgawaY, EbiharaK, AizawaAbeM, MiyanagaF, TakayaK, HayashiT, InoueG, HosodaK, KojimaM, KangawaK, NakaoK.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. Diabetes50: 227–232, 2001.
25.
MercerJG, HoggardN, WilliamsLM, LawrenceCB, HannahLT, MorganPJ, TrayhurnP.Coexpression of leptin receptor and preproneuropeptide Y mRNA in arcuate nucleus of mouse hypothalamus. J Neuroendocrinol8: 733–735, 1996.
26.
TrayhurnP, ThomasMEA, DuncanJS, RaynerDV. Effects of fasting and refeeding on ob gene expression in white adipose tissue of lean and obese (ob/ob) mice. FEBS Lett368: 488–490, 1995.
27.
ChuaSC, ChungWK, WupengXS, ZhangYY, LiuSM, TartagliaL, LeibelRL. Phenotypes of mouse diabetes and rat fatty due to mutations in the OB (leptin) receptor. Science271: 994–996, 1996.
28.
BeckB.Neuropeptides and obesity. Nutrition16: 916–923, 2000.
29.
BeckB, BurletA, NicolasJP, BurletC.Hyperphagia in obesity is associated with a central peptidergic dysregulation in rats. J Nutr120: 806–811, 1990.
30.
BeckB, BurletA, NicolasJP, BurletC.Galanin in the hypothalamus of fed and fasted lean and obese Zucker rats. Brain Res623: 124–130, 1993.
31.
BeckB, RichyS, DimitrovT, Stricker-KrongradA.Opposite regulation of hypothalamic orexin and neuropeptide Y receptors and peptide expressions in obese Zucker rats. Biochem Biophys Res Commun286: 518–523, 2001.
32.
Stricker-KrongradA, DimitrovT, BeckB.Central and peripheral dysregulation of melanin-concentrating hormone in obese Zucker rats. Mol Brain Res92: 43–48, 2001.
33.
BeckB, MusseN, Stricker-KrongradA.Ghrelin, macronutrient intake and dietary preferences in Long-Evans rats. Biochem Biophys Res Commun292: 1031–1035, 2002.
34.
UkkolaO, RavussinE, JacobsonP, SnyderEE, ChagnonM, SjostromL, BouchardC.Mutations in the preproghrelin/ghrelin gene associated with obesity in humans. J Clin Endocrinol Metab86: 3996–3999, 2001.
35.
TschopM, WeyerC, TataranniPA, DevanarayanV, RavussinE, HeimanML. Circulating ghrelin levels are decreased in human obesity. Diabetes50: 707–709, 2001.
36.
MartinRJ, GahaganJ.Serum hormone levels and tissue metabolism in pair-fed and obese Zucker rats. Horm Metab Res9: 181–186, 1977.
37.
SobhaniI, BadoA, VissuzaineC, BuyseM, KermorgantS, LaigneauJP, AttoubS, LehyT, HeninD, MignonM, LewinMJM. Leptin secretion and leptin receptor in the human stomach. Gut47: 178–183, 2000.
38.
MixH, WidjajaA, JandlO, CornbergM, KaulA, GokeM, BeilW, KuskeM, BrabantG, MannsMP, WagnerS.Expression of leptin and leptin receptor isoforms in the human stomach. Gut47: 481–486, 2000.
39.
BadoA, LevasseurS, AttoubS, KermorgantS, LaigneauJP, BortoluzziMN, MoizoL, LehyT, Guerre-MilloM, LeMarchandBrustelY, LewinMJM. The stomach is a source of leptin. Nature394: 790–793, 1998.
40.
HahnTM, BreiningerJF, BaskinDG, SchwartzMW. Coexpression of Agrp and NPY in fasting-activated hypothalamic neurons. Nat Neurosci1: 271–272, 1998.
41.
TschopM, StatnickMA, SuterTM, HeimanML. GH-releasing peptide-2 increases fat mass in mice lacking NPY: Indication for a crucial mediating role of hypothalamic agouti-related protein. Endocrinology143: 558–568, 2002.
42.
KornerJ, SavontausE, ChuaSC, LeibelRL, WardlawSL. Leptin regulation of Agrp and Npy mRNA in the rat hypothalamus. J Neuroendocrinol13: 959–966, 2001.
43.
BeckB, BurletA, NicolasJP, BurletC.Unexpected regulation of hypothalamic neuropeptide-Y by food deprivation and refeeding in the Zucker rat. Life Sci50: 923–930, 1992.
44.
BagnascoM, KalraPS, KalraSP. Ghrelin and leptin pulse discharge in fed and fasted rats. Endocrinology143: 726–729, 2002.
45.
TolleV, BassantMH, ZizzariP, PoindessousJazatF, TomasettoC, EpelbaumJ, BluetPajotMT. Ultradian rhythmicity of ghrelin secretion in relation with GH, feeding behavior, and sleep-wake patterns in rats. Endocrinology143: 1353–1361, 2002.
