Ghrelin Stimulates Gastric Emptying and Hunger in Normal-Weight Humans

0021-972X/06/$15.00/0 Printed in U.S.A. The Journal of Clinical Endocrinology & Metabolism 91(9):3296 –3302 Copyright © 2006 by The Endocrine Society doi: 10.1210/jc.2005-2638 Ghrelin Stimulates Gastric Emptying and Hunger in Normal-Weight Humans F. Levin, T. Edholm, P. T. Schmidt, P. Grybäck, H. Jacobsson, M. Degerblad, C. Höybye, J. J. Holst, J. F. Rehfeld, P. M. Hellström, and E. Näslund Context: Ghrelin is produced primarily by enteroendocrine cells in the gastric mucosa and increases gastric emptying in patients with gastroparesis. Main Objective: The objective of the study was to evaluate the effect of ghrelin on gastric emptying, appetite, and postprandial hormone secretion in normal volunteers. Design: This was a randomized, double-blind, crossover study. Subjects: Subjects included normal human volunteers and patients with GH deficiency. Intervention: Intervention included saline or ghrelin (10 pmol/ kg䡠min) infusion for 180 min after intake of a radioactively labeled omelette (310 kcal) or GH substitution in GH-deficient patients. Main Outcome Measures: Measures consisted of gastric empty- G HRELIN WAS DISCOVERED as the endogenous ligand to the orphan G protein-coupled GH secretagogue receptor (GHS-R) and demonstrated to specifically stimulate GH release from rat pituitary cells in vitro as well as in vivo (1, 2). From the GHS-R gene, two mRNAs are produced, which are translated into two distinct proteins that have been named GHS-R1a and GHS-R1b. The GHSR1a, now named the ghrelin receptor, is a typical G proteincoupled seven-transmembrane domain receptor. The GHSR1b is a truncated receptor with only five transmembrane domains and is pharmacologically inactive (3). In situ hybridization indicated that ghrelin was elaborated in and released from enteroendocrine X/A-like cells in the gastric mucosa (4) to circulate in human blood at a considerable concentration (1). However, in addition, ghrelin-containing neural cells are localized in the arcuate nucleus of the hypothalamus, which is a well-known center for feeding regFirst Published Online June 13, 2006 Abbreviations: CCK, Cholecystokinin; GHD, GH-deficient; GHS-R, GH secretagogue receptor; GLP, glucagon-like peptide; NPY, neuropeptide Y; PYY, peptide YY; T50, half-emptying time; VAS, visual analog scores. JCEM is published monthly by The Endocrine Society (http://www. endo-society.org), the foremost professional society serving the endocrine community. ing parameters and postprandial plasma levels of ghrelin, cholecystokinin, glucagon-like peptide-1, peptide YY, and motilin. Results: The emptying rate was significantly faster for ghrelin (1.26 ⫾ 0.1% per minute), compared with saline (0.83% per minute) (P ⬍ 0.001). The lag phase (16.2 ⫾ 2.2 and 26.5 ⫾ 3.8 min) and half-emptying time (49.4 ⫾ 3.9 and 75.6 ⫾ 4.9 min) of solid gastric emptying were shorter during ghrelin infusion, compared with infusion of saline (P ⬍ 0.001). The postprandial peak in plasma concentration for cholecystokinin and glucagon-like peptide-1 occurred earlier and was higher during ghrelin infusion. There was no significant effect of ghrelin on plasma motilin or peptide YY. There was no difference in gastric emptying before and after GH substitution. Conclusion: Our results demonstrate that ghrelin increases the gastric emptying rate in normal humans. The effect does not seem to be mediated via GH or motilin but may be mediated by the vagal nerve or directly on ghrelin receptors in the stomach. Ghrelin receptor agonists may have a role as prokinetic agents. (J Clin Endocrinol Metab 91: 3296–3302, 2006) ulation, suggesting involvement in the regulation of feeding (5, 6). Peripheral administration of ghrelin causes weight gain by reducing fat use and stimulating food intake in rats (2), and serum ghrelin concentrations are increased by fasting and reduced by refeeding in rats and humans (7). Serum ghrelin rises sharply before and falls within 1 h of a meal (8). Several studies on rats and humans confirm that ghrelin initiates food intake (9, 10), and circulating ghrelin levels are increased by up to 3-fold in states of negative energy balance, such as anorexia nervosa, starvation, cachexia, and also after weight loss in obesity (11) and are, conversely, decreased in conditions such as obesity, hyperglycemia, and feeding (12, 13), suggesting that ghrelin plays a central role in the shortand long-term energy homeostasis (14). Additional data indicate that ghrelin also plays a role in the regulation of gastrointestinal motility and acid secretion. Thus, iv administration of ghrelin stimulates gastric motility as well as acid secretion in rats, and the effect is abolished by pretreatment with atropine or bilateral cervical vagotomy (15–18). Several studies also show a significant acceleration of solid gastric emptying in rats (18 –20) and mice (21, 22). However, the results in dogs are not unequivocal as stimulation (23) and recently lack of effect have been reported (24). Because gastric emptying rate and the sensation of hunger 3296 Division of Surgery (F.L., E.N.), Danderyd Hospital, Karolinska Institutet, SE-182 88 Stockholm, Sweden; Departments of Gastroenterology and Hepatology (T.E., P.T.S., P.M.H.), Nuclear Medicine (P.G., H.J.), and Molecular Medicine and Surgery (M.D., C.H.), Karolinska University Hospital Solna, Karolinska Institutet, SE-171 77 Stockholm, Sweden; Department of Medical Physiology (J.J.H.), University of Copenhagen, DK-2200 Copenhagen, Denmark; and Department of Clinical Biochemistry (J.F.R.), Rigshospitalet, University of Copenhagen, DK-2100 Copenhagen, Denmark Levin et al. • Ghrelin Stimulates Gastric Emptying Subjects and Methods Subjects Solid scintigraphic gastric emptying and plasma concentrations of gut peptides were studied in eight healthy, nonsmoking volunteers (five men, three women, 26.5 ⫾ 1.6 yr), with a mean body mass index of 24.0 ⫾ 1.1 kg/m2. Solid scintigraphic gastric emptying was also studied in six GHD patients (three men, 58.3 ⫾ 3.0 yr) before and after 6 months of GH substitution therapy. All patients had GHD of adult onset. They all had a medical history of pituitary adenomas treated by transphenoidal surgery and/or pituitary irradiation. The diagnosis of GHD was confirmed by provocation test (insulin-induced hypoglycemia or arginine test) with a low GH response (⬍3 mg/liter). The GH substitution dose used increased the serum IGF-I values to levels within the age-matched range. RT-PCR for ghrelin and the two subtypes of the ghrelin receptor was performed in human stomach (fundus, n ⫽ 3; corpus, n ⫽ 3; antrum, n ⫽ 6) obtained from patients undergoing gastric resection for cancer (n ⫽ 6). The study protocol was approved by the Ethics Committee of the Karolinska Institutet North, and all subjects gave written informed consent. Solid gastric emptying The study was performed in a randomized, double-blind, placebocontrolled crossover fashion on two occasions with a washout interval (...truncated)