Serum Ghrelin Levels in Response to Glucose ... - Wiley Online Library

Short Communication

Serum Ghrelin Levels in Response to Glucose Load in Obese Subjects Post-Gastric Bypass Surgery Nicholas A. Tritos,*‡ Edward Mun,†‡ Anne Bertkau,* Rebecca Grayson,* Eleftheria Maratos-Flier,*‡ and Allison Goldfine*‡

Abstract TRITOS, NICHOLAS A., EDWARD MUN, ANNE BERTKAU, REBECCA GRAYSON, ELEFTHERIA MARATOS-FLIER, AND ALLISON GOLDFINE. Serum ghrelin levels in response to glucose load in obese subjects post-gastric bypass surgery. Obes Res. 2003;11:919 –924. Objective: We sought to elucidate further the mechanisms leading to weight loss after gastric bypass (GBP) surgery in morbidly obese individuals. Ghrelin is a gastroenteric appetite-stimulating peptide hormone, fasting levels of which decrease with increasing adiposity and increase with dietinduced weight loss. In addition, ghrelin levels rapidly decline postprandially. Research Methods and Procedures: We measured serum ghrelin responses to a 75-g oral glucose tolerance test (OGTT) in 6 subjects who had undergone GBP surgery 1.5 ⫾ 0.7 years before testing and compared these responses with 6 obese subjects about to undergo GBP surgery, 6 obese nonsurgical subjects (matched for BMI to the postGBP surgical group), and 5 lean subjects. Results: Despite weight loss induced by the GBP surgery, fasting serum ghrelin levels were significantly lower in the post-GBP surgery group than in the lean subject (by 57%) or pre-GBP surgery (by 45%) group. Serum ghrelin levels during the OGTT were significantly lower in postoperative than in lean, obese pre-GBP surgical, or obese nonsurgical subjects. The magnitude of the decline in serum ghrelin levels between 0 and 120 minutes post-OGTT was significantly smaller in postoperative (by 62%), obese pre-GBP

Received for review February 19, 2003. Accepted in final form May 27, 2003. *Joslin Diabetes Center, Boston, Massachusetts; †Department of Surgery, Beth Israel Deaconess Medical Center, Boston, Massachusetts; and ‡Harvard Medical School, Boston, Massachusetts. Address correspondence to Allison Goldfine, Joslin Diabetes Center, One Joslin Place, Boston, MA 02215. E-mail: [email protected] Copyright © 2003 NAASO

surgical (by 80%), or obese nonsurgical (by 69%) subjects in comparison with lean subjects. Discussion: Serum ghrelin levels in response to OGTT are lower in subjects post-GBP surgery than in either lean or obese subjects. Tonically low serum ghrelin levels may be involved in the mechanisms inducing sustained weight loss after GBP surgery. Key words: gastric bypass surgery, ghrelin

Introduction

Obesity, defined as a BMI of over 30 kg/m2, currently affects ⬃25% of the adult U.S. population and is associated with substantial morbidity and mortality (1–3). Morbid obesity (BMI over 40 kg/m2) is less common but is usually resistant to medical therapy (2). Gastric bypass (GBP)1 surgery is very effective in inducing sustained weight loss in the majority of morbidly obese patients, leading to loss of approximately 60% of excess body weight at 10-year follow-up, and has been endorsed by the NIH Consensus Development Panel as effective in causing weight reduction (4 – 6). The mechanisms leading to weight loss after GBP surgery have not been clearly established. Early distention of the small gastric pouch by limited amounts of food may lead to satiety (5). In addition, modest malabsorption may occur as a result of the gastrojejunostomy and bypass of the duodenal loop (5). However, the potential endocrine changes after surgery that might mediate neuroendocrine signaling are largely unknown. Ghrelin is a 28-amino acid appetite-stimulating hormone primarily secreted from the gastric fundic mucosa, originally discovered as an endogenous ligand of the growth hormone secretagogue receptor (7–10). It has been suggested that circulating ghrelin levels increase before meals,

1

Nonstandard abbreviations: GBP, gastric bypass; OGTT, oral glucose tolerance testing.

OBESITY RESEARCH Vol. 11 No. 8 August 2003

919

Low Serum Ghrelin after Gastric Bypass Surgery, Tritos et al.

contributing to meal initiation, and rapidly decline postprandially, contributing to satiety (11,12). Although the mechanisms regulating ghrelin expression have not been established, it is known that ingestion or gastric infusion of nutrients suppresses ghrelin secretion and systemic ghrelin levels (10,11,13–15). In addition, fasting serum ghrelin levels correlate inversely with increasing BMI and increase in response to medically induced weight loss (16 –18), an increase which may contribute to increased appetite commonly seen with weight loss. Paradoxically, a recent study demonstrated that, after GBP surgery for morbid obesity, plasma ghrelin levels fell to below those seen in normal subjects and that the typical diurnal variation normally seen was significantly blunted (15). In the present study, we sought to examine further the role of ghrelin in weight loss after GBP surgery. We investigated the circulating ghrelin excursion in response to nutrient challenge during oral glucose tolerance testing (OGTT) in subjects who had previously undergone GBP surgery leading to weight loss, in comparison with serum ghrelin profiles on OGTT in obese subjects about to undergo GBP surgery and in healthy obese (matched for BMI to the post-GBP subjects) and lean control subjects.

Research Methods and Procedures Subjects Study subjects were consecutively recruited among adult patients who had undergone GBP surgery for morbid obesity at the Beth Israel Deaconess Medical Center in Boston. Morbidly obese adults about to undergo GBP surgery at the Beth Israel Deaconess Medical Center and healthy adult obese (BMI over 30 kg/m2) and lean (BMI between 19 and 25 kg/m2) volunteers were recruited as control groups. The exclusion criteria for the study included current or past congestive heart failure, chronic liver or kidney disease, any malignancy, acute infection or injury, current pregnancy, and use of any medications that could affect insulin sensitivity other than oral hypoglycemic agents. The study was approved by the local institution committees on human studies, and all subjects gave written informed consent. All subjects completed the study without complications. The subjects’ height and weight were measured using a wall-mounted stadiometer (Holtain Ltd., Crymych, UK) and a 270-kg capacity electronic scale (model 0501, ACME, San Leandro, CA), respectively. The presence of type 2 diabetes or impaired glucose tolerance was defined according to the current American Diabetes Association criteria (19 –21). OGTT Study subjects underwent a 2-hour, 75-g OGTT at the Clinical Research Center of the Joslin Diabetes Center starting at 8 AM after a 12-hour fast. All subjects, including 920


subjects post-GBP surgery, were instructed to and were able to consume a diet with sufficient carbohydrates (200 g daily) for 3 days before the study. Medications were withheld on the morning of testing. Blood samples were collected (in serum separator tubes) by venupuncture in the fasting state and 30, 60, and 120 minutes after a 75-g oral glucose load. Blood samples were promptly spun in a tabletop centrifuge, and the sera were frozen at ⫺70 °C until assayed. Additional blood samples were collected in fluoride containing tubes for plasma glucose assay using a standard laboratory autoanalyzer (Beckman, Fullerton, CA), and bedside blood glucose readings were concurrently obtained for safety monitoring during OGTT using a bedside glucometer (One Touch, Johnson and Johnson, Milpitas, CA). Hormone Assays Serum ghrelin was measured using a commercially available radioimmunoassay for total ghrelin, according to the manufacturer’s instructions (Phoenix Pharmaceuticals, Inc., Belmont, CA). Bound radioactivity was measured in a COBRA gamma counter (Hewlett Packard, Palo Alto, CA). The sensitivity for the ghrelin assay is 5.9 pM (20 pg/mL), the intra-assay coefficient of variation is 9%, and the interassay coefficient of variation is 15%. Statistics Continuous variables are displayed as mean ⫾ SE. Analyses of normally distributed continuous variables were performed using paired Student’s t test, ANOVA, or repeated measures ANOVA as appropriate, with Fisher’s least significant difference post hoc analysis. In addition, analyses involving nominal variables were performed using Fisher’s exact test. All analyses, performed using the Statview 5 statistical package (SAS Institute, Cary, NC), were twotailed, and p values of ⬍0.05 were considered statistically significant.

Results Twenty-three subjects (28.5 to 70.5 years, 14 females and 9 males), including 6 subjects who had undergone GBP surgery for morbid obesity (1.5 ⫾ 0.7 years before enrollment into the study, BMI range: 27.8 to 39.3 kg/m2), 6 obese subjects about to undergo GBP surgery for morbid obesity (BMI range: 38.4 to 55.8 kg/m2), and 6 obese nonsurgical (BMI range: 30.7 to 39.9 kg/m2) and 5 lean (BMI range: 19.5 to 23.7 kg/m2) subjects were consecutively enrolled in the study. The baseline characteristics of the study population are shown in Table 1. There was no significant difference in age, gender distribution, height, fasting glucose levels, or 2-hour post-OGTT glucose levels among the 4 subject groups. By selection, current body weight and current BMI were significantly higher in all three obese cohorts than in


Table 1. Baseline characteristics of the study population Variable Age (years) Gender (male/female) Height (m) Weight (kg) Preoperative BMI (kg/m2) BMI (kg/m2) Fasting plasma glucose (mM) 2-hour plasma glucose (mM) Fasting plasma insulin (␮U/ml)

Pre-GBP group

Post-GBP group

Obese nonsurgical group

Lean group

P Value

38.9 ⫾ 3.9 5/1 1.68 ⫾ 0.02 128.9 ⫾ 9.3 45.3 ⫾ 2.8 45.3 ⫾ 2.8 6.4 ⫾ 0.5 9.5 ⫾ 1.3†‡ 60.9 ⫾ 3.2

45.2 ⫾ 4.0 3/3 1.70 ⫾ 0.01 101.2 ⫾ 4.8 55.6 ⫾ 1.1 35.0 ⫾ 1.7 5.5 ⫾ 0.6 5.5 ⫾ 1.1† 5.9 ⫾ 1.4

48.5 ⫾ 6.5 4/2 1.72 ⫾ 0.04 101.3 ⫾ 6.2 NA 33.8 ⫾ 1.4 5.9 ⫾ 0.4 8.1 ⫾ 1.7 10.4 ⫾ 1.3

46.1 ⫾ 6.2 1/4 1.61 ⫾ 0.03 57.9 ⫾ 4.2 NA 21.9 ⫾ 0.8 4.6 ⫾ 0.2 5.6 ⫾ 0.5‡ 6.8 ⫾ 1.5

NS NS NS ⬍0.0001* 0.006 ⬍0.0001* NS NS ⬍0.005*

NA, not applicable; NS, not significant. * Only overall P values are shown in the table (by ANOVA). Pair-wise post hoc comparisons are shown in text. †,‡ p ⬍ 0.05 using Student’s t test. However, these differences are not significant using ANOVA (for multiple comparisons).

the lean group (p ⬍ 0.0001). Body weight and current BMI were both significantly higher in the pre-GBP obese group than in the post-GBP obese group (p ⬍ 0.007) and the obese nonsurgical control (p ⬍ 0.007) group. There was no difference in body weight or BMI between the post-GBP obese group and the obese nonsurgical control group (p ⫽ not significant). Post-GBP surgery subjects had lost 59.4 ⫾ 2.9 kg because of GBP surgery (p ⬍ 0.0001 for the difference between preoperative and postoperative body weight). Four pre-GBP subjects had lost a mean of 2.3 kg (range: 0.5 to 4.8 kg), and two pre-GBP subjects had gained a mean of 2.8 kg (range: 1.0 to 4.7 kg) over a mean period of 3.3 months (range: 2 to 5 months) before the study. Two pre-GBP obese subjects, one post-GBP subject, and two obese (nonsurgical group) subjects had type 2 diabetes. Of the subjects with diabetes, one pre-GBP obese subject was receiving metformin, and the other was receiving glipizide. Similarly, of the obese (nonsurgical) subjects with diabetes, one was treated with metformin, and the other was treated with glipizide. The post-GBP surgical patient was not on pharmacological therapy for diabetes. Two obese pre-GBP subjects and one obese (nonsurgical group) subject had impaired glucose tolerance. Serum ghrelin levels during OGTT are shown in Figure 1. Fasting serum ghrelin levels were 57% lower in the postGBP surgery group than in the lean subject group (p ⬍ 0.0001) and 45% lower in the post-GBP surgery group than in the pre-GBP surgery group (p ⫽ 0.0002). In addition, fasting serum ghrelin levels were 40% higher in the preGBP surgery obese group than in the obese nonsurgical group (p ⫽ 0.008). In contrast, fasting serum ghrelin levels were 43% lower in the obese nonsurgical than in the lean subjects (p ⫽ 0.0004).

Despite weight loss induced by GBP surgery, serum ghrelin levels during the OGTT were significantly lower in the post-GBP surgery group than in the obese nonsurgical group (p ⫽ 0.0002), the pre-GBP surgery group (p ⬍ 0.0001), or the lean subject group (p ⬍ 0.0001) (Figure 1). Serum ghrelin levels during OGTT were significantly higher in the pre-GBP surgery obese group than the obese nonsurgical subjects (p ⬍ 0.0001). In addition, serum

Figure 1: Serum ghrelin levels during OGTT in the study population, showing significantly lower serum ghrelin in the post-GBP surgery group than in the obese nonsurgical (p ⫽ 0.0002), the pre-GBP surgery group (p ⬍ 0.0001), or lean (p ⬍ 0.0001) subject group. Serum ghrelin levels during OGTT were significantly higher in the pre-GBP surgery obese group than the obese nonsurgical subjects (p ⬍ 0.0001). In addition, serum ghrelin levels during OGTT were significantly lower in the obese nonsurgical than the lean subjects (p ⬍ 0.0001).


921


Figure 2: Data on the magnitude of the decline in serum ghrelin levels between 0 and 120 minutes post-OGTT (⌬ serum ghrelin 0 to 120), showing significantly smaller “⌬ serum ghrelin 0 to 120 minutes” in post-GBP (by 62%, p ⫽ 0.0002), pre-GBP subjects (by 80%, p ⬍ 0.0001), and obese nonsurgical (by 69%, p ⫽ 0.0001) subjects in comparison with lean subjects.

ghrelin levels during OGTT were significantly lower in the obese nonsurgical than the lean subjects (p ⬍ 0.0001) (Figure 1). There was no significant difference in serum ghrelin levels during the OGTT between the four pre-GBP subjects who had weight loss and the two pre-GBP subjects who had weight gain preoperatively (p ⫽ not significant, data not shown). The magnitude of the decline in serum ghrelin levels between 0 and 120 minutes post-OGTT (⌬ 0 to 120) was significantly smaller in post-GBP subjects (by 62%, p ⫽ 0.0002), in pre-GBP subjects (by 80%, p ⬍ 0.0001), and in obese nonsurgical subjects (by 69%, p ⫽ 0.0001) in comparison with lean subjects (Figure 2).

Discussion The mechanisms leading to sustained weight loss after GBP surgery for morbid obesity are poorly understood and have historically been attributed to the mechanical effect of reducing the volume of the stomach (5). The discovery of ghrelin, a systemic hormone secreted primarily by the stomach, whose daily fluctuations seem to signal meal-time hunger, suggested that the stomach may play a role as an endocrine organ, signaling the brain regarding the acute availability of energy stores (7,11,22). Furthermore, the discovery of ghrelin has helped redefine our understanding of the regulation of appetite and body adiposity and the possible mechanisms by which GBP surgery leads to successful weight loss (7,11,15,22,23). In addition to being an orexigenic signal, ghrelin may also have long-term effects on the regulation of body adiposity (22). This hypothesis is supported by human crosssectional data suggesting that fasting serum ghrelin levels are regulated by body adiposity and by animal data suggest922


ing that long-term ghrelin administration leads to an increase in body weight, mediated through increased appetite and respiratory quotient (decreased fat oxidation) (10,16,18,24 –27). A recent study compared morbidly obese subjects who had lost weight after GBP surgery with normal-weight subjects and with obese subjects who had lost weight through conventional diet. This study demonstrated that serum ghrelin profiles, measured by frequent venous blood sampling over 24 hours, were dramatically lower after GBP surgery in comparison with serum ghrelin profiles of lean subjects or matched-obese subjects, despite sustained weight loss in the post-GBP surgical group (15). In contrast, after dietary weight loss, subjects showed higher circulating ghrelin levels. This study suggested that lowering of serum ghrelin levels may be involved in the mechanisms inducing weight loss after GBP surgery, possibly by affecting appetite and the initiation of meals (15). It has been suggested, however, that additional data would be required, including the restoration of appetite by exogenous physiological ghrelin replacement in GBP patients, to make the ghrelin hypothesis compelling (28). In the present study, we examined serum ghrelin profiles in response to a glucose load in subjects who had lost weight as a result of GBP surgery and compared these subjects with persons of normal weight and with obese individuals about to undergo GBP surgery and obese individuals with stable body weight. We have demonstrated lower serum ghrelin levels in post-GBP subjects than in both lean and the two obese (obese pre-GBP as well as obese nonsurgical) subject groups, despite weight loss in the post-GBP group. In contrast, diet-induced weight loss has been shown to lead to an increase in serum ghrelin levels (15,17). In addition to confirming previous data (14), our findings suggest that the decline in serum ghrelin levels after GBP surgery is even more dramatic in comparison with serum ghrelin profiles in obese pre-GBP subjects than in obese nonsurgical subjects. In addition, these morbidly obese (preGBP) subjects had higher serum ghrelin levels than obese nonsurgical subjects despite lower BMI in the obese nonsurgical group. These findings further suggest that serum ghrelin levels may be increased in morbidly obese individuals, in contrast to the previously established decrease in serum ghrelin levels with increasing adiposity (12). It is tempting to speculate that differential regulation of serum ghrelin levels in morbid obesity may contribute to weight gain in this group. However, further studies are required to clarify this issue. The significance of low serum ghrelin levels after GBP surgery has not been established definitively. Previous data suggest that a ghrelin infusion leads to an acute increase in appetite and food intake in humans (29). Therefore, a persistent decrease in serum ghrelin levels post-GBP surgery


may lead to a decrease in appetite, contributing to sustained weight loss and preventing weight regain in postoperative patients. The physiological role of ghrelin among lean subjects is still being investigated. Differences in hypothalamic sensitivity to systemic ghrelin may exist between lean and obese subjects, explaining why lean subjects may not gain weight, despite higher serum ghrelin levels. This issue clearly merits further study. The mechanisms leading to decreased serum ghrelin levels after GBP surgery are unknown. It is conceivable that the creation of a small gastric pouch during GBP surgery disrupts ghrelin secretory mechanisms, presumably by excluding a large portion of the stomach, including the gastric fundus (a major source of circulating ghrelin), from the rest of the gastrointestinal tract (8,22). The precise mechanisms underlying the change in serum ghrelin levels post-GBP surgery require further study. Although our study was relatively small and cross-sectional, it is nevertheless strengthened by the inclusion of two control groups. Two prospective investigations of subjects undergoing GBP surgery have been published recently and have reported conflicting results on the change in fasting serum ghrelin levels post-GBP surgery (30,31). Thus far, three of the four currently available studies (including ours) have suggested that serum ghrelin levels are decreased post-GBP surgery (15,30,31). The reasons for the discrepancy between one of the two prospective studies and the other three available studies are unclear. However, neither of the two prospective studies included subjects losing weight on diet alone (30,31). Larger prospective investigations of morbidly obese subjects undergoing GBP surgery in comparison with obese subjects losing weight on diet alone are required to establish the role of ghrelin in energy homeostasis post-GBP surgery more definitively. In summary, we found that serum ghrelin levels are low in post-GBP surgery subjects despite weight loss (which increases ghrelin levels when achieved by diet alone) and may be involved in the mechanisms inducing sustained weight loss after GBP surgery. Further elucidating the pathways and signals mediating weight loss after GBP surgery may lead to characterization of new potential drug targets and the design of novel therapeutic agents for obesity.

Acknowledgments This research study was supported in part by NIH Grant M0 1 RR 01032 to the Beth Israel Deaconess Medical Center General Clinical Research Center, the Joslin Diabetes Center Clinical Research Center Satellite, and the Donner Foundation. A. G. was supported in part by K23DK02795. E. M.-F. was supported by research grants from the NIH (DK53978 and DK56113) and is a principal Investigator on program project DK56116 (NIH/National Institute of Diabetes, Digestive and Kidney Diseases). Dr. N.

Tritos was supported in part by the Clinical Investigator Training Program, Beth Israel Deaconess Medical Center, and the Harvard-Massachusetts Institute of Technology Division of Health Sciences and Technology (Boston, MA) in collaboration with Pfizer, Inc. References 1. Flegal KM, Carroll MD, Kuczmarski RJ, Johnson CL. Overweight and obesity in the United States: prevalence and trends, 1960 –1994. Int J Obes Relat Metab Disord. 1998;22: 39 – 47. 2. Willett WC, Dietz WH, Colditz GA. Guidelines for healthy weight. N Engl J Med. 1999;341:427–34. 3. Flegal KM, Carroll MD, Ogden CL, Johnson CL. Prevalence and trends in obesity among US adults, 1999 –2000. JAMA. 2002;288:1723–7. 4. Mason EE, Ito C. Gastric bypass in obesity. Obes Res. 1996;4:316 –9. 5. Mun EC, Blackburn GL, Matthews JB. Current status of medical and surgical therapy for obesity. Gastroenterology. 2001;120:669 – 81. 6. NIH Conference. Gastrointestinal surgery for severe obesity: Consensus Development Conference Panel. Ann Intern Med. 1991;115:956 – 61. 7. Kojima M, Hosoda H, Date Y, Nakazato M, Matsuo H, Kangawa K. Ghrelin is a growth-hormone-releasing acylated peptide from stomach. Nature. 1999;402:656 – 60. 8. Asakawa A, Inui A, Kaga T, et al. Ghrelin is an appetitestimulatory signal from stomach with structural resemblance to motilin. Gastroenterology. 2001;120:337– 45. 9. Ariyasu H, Takaya K, Tagami T, et al. Stomach is a major source of circulating ghrelin, and feeding state determines plasma ghrelin-like immunoreactivity levels in humans. J Clin Endocrinol Metab. 2001;86:4753– 8. 10. Tschop M, Smiley DL, Heiman ML. Ghrelin induces adiposity in rodents. Nature. 2000;407:908 –13. 11. Tschop M, Wawarta R, Riepl RL, et al. Post-prandial decrease of circulating human ghrelin levels. J Endocrinol Invest. 2001;24:RC19 –21. 12. Cummings DE, Purnell JQ, Frayo RS, Schmidova K, Wisse BE, Weigle DS. A preprandial rise in plasma ghrelin levels suggests a role in meal initiation in humans. Diabetes. 2001;50:1714 –9. 13. Kojima M, Hosoda H, Matsuo H, Kangawa K. Ghrelin: discovery of the natural endogenous ligand for the growth hormone secretagogue receptor. Trends Endocrinol Metab. 2001;12:118 –22. 14. Shiiya T, Nakazato M, Mizuta M, et al. Plasma ghrelin levels in lean and obese humans and the effect of glucose on ghrelin secretion. J Clin Endocrinol Metab. 2002;87:240 – 4. 15. Cummings DE, Weigle DS, Frayo RS, et al. Plasma ghrelin levels after diet-induced weight loss or gastric bypass surgery. N Engl J Med. 2002;346:1623–30. 16. Tschop M, Weyer C, Tataranni PA, Devanarayan V, Ravussin E, Heiman ML. Circulating ghrelin levels are decreased in human obesity. Diabetes. 2001;50:707–9. 17. Hansen TK, Dall R, Hosoda H, et al. Weight loss increases circulating levels of ghrelin in human obesity. Clin Endocrinol. 2002;56:203– 6. OBESITY RESEARCH Vol. 11 No. 8 August 2003

923


18. Nakazato M, Murakami N, Date Y, et al. A role for ghrelin in the central regulation of feeding. Nature. 2001;409:194 – 8. 19. Harris MI, Eastman RC, Cowie CC, Flegal KM, Eberhardt MS. Comparison of diabetes diagnostic categories in the U. S. population according to the 1997 American Diabetes Association and 1980 –1985 World Health Organization diagnostic criteria. Diabetes Care. 1997;20:1859 – 62. 20. Guillausseau PJ. Classification and diagnostic criteria of diabetes: propositions of ADA and WHO. Diabetes Metab. 1997;23:454 –5. 21. Puavilai G, Chanprasertyotin S, Sriphrapradaeng A. Diagnostic criteria for diabetes mellitus and other categories of glucose intolerance: 1997 criteria by the Expert Committee on the Diagnosis and Classification of Diabetes Mellitus (ADA), 1998 WHO consultation criteria, and 1985 WHO criteria. World Health Organization. Diabetes Res Clin Pract. 1999; 44:21– 6. 22. Inui A. Ghrelin: an orexigenic and somatotrophic signal from the stomach. Nat Rev Neurosci. 2001;2:551– 60. 23. Sugino T, Yamaura J, Yamagishi M, et al. A transient surge of ghrelin secretion before feeding is modified by different feeding regimens in sheep. Biochem Biophys Res Commun. 2002;298:785– 8. 24. Shintani M, Ogawa Y, Ebihara K, et al. Ghrelin, an endogenous growth hormone secretagogue, is a novel orexigenic peptide that antagonizes leptin action through the activation of

924


25.

26.

27.

28. 29.

30.

31.

hypothalamic neuropeptide Y/Y1 receptor pathway. Diabetes. 2001;50:227–32. Bagnasco M, Tulipano G, Melis MR, Argiolas A, Cocchi D, Muller EE. Endogenous ghrelin is an orexigenic peptide acting in the arcuate nucleus in response to fasting. Regul Pept. 2003;111:161–7. Murakami N, Hayashida T, Kuroiwa T, et al. Role for central ghrelin in food intake and secretion profile of stomach ghrelin in rats. J Endocrinol. 2002;174:283– 8. Shuto Y, Shibasaki T, Otagiri A, et al. Hypothalamic growth hormone secretagogue receptor regulates growth hormone secretion, feeding, and adiposity. J Clin Invest. 2002;109:1429 – 36. Flier JS, Maratos-Flier E. The stomach speaks– ghrelin and weight regulation. N Engl J Med. 2002;346:1662–3. Wren AM, Seal LJ, Cohen MA, et al. Ghrelin enhances appetite and increases food intake in humans. J Clin Endocrinol Metab. 2001;86:5992. Geloneze B, Tambascia MA, Pilla VF, Geloneze SR, Repetto EM, Pareja JC. Ghrelin: a gut-brain hormone: effect of gastric bypass surgery. Obes Surg. 2003;13:17–22. Faraj M, Havel PJ, Phelis S, Blank D, Sniderman AD, Cianflone K. Plasma acylation-stimulating protein, adiponectin, leptin, and ghrelin before and after weight loss induced by gastric bypass surgery in morbidly obese subjects. J Clin Endocrinol Metab. 2003;88:1594 – 602.