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Effect of Peptide YY3–36 on Food Intake in Humans

2005; Elsevier BV; Volume: 129; Issue: 5 Linguagem: Inglês

10.1053/j.gastro.2005.09.001

1528-0012

Lukas Degen, Sibylle Oesch, Michel Casanova, Stefanie Graf, Silvia Ketterer, Jürgen Drewe, Christoph Beglinger,

Neuropeptides and Animal Physiology

Background & Aims: Studies in animals and humans suggest a role for peptide YY (PYY3–36) in regulating satiety. The physiologic role of PYY3–36, however, has not been investigated in detail. Methods: The present study was designed to examine PYY release in response to 2 meals differing in their calorie content and to relate the plasma levels to those obtained after exogenous infusion. In a second step, the effect of graded intravenous doses (0, 0.2, 0.4, and 0.8 pmol · kg−1 · min−1) of synthetic human PYY3–36 on food intake was investigated in healthy male volunteers in a double-blind, placebo-controlled fashion. Results: Plasma PYY concentrations increased in response to food intake reflecting the size of the calorie load. Graded PYY3–36 infusions resulted in a dose-dependent reduction in food intake (maximal inhibition, 35%; P < .001 vs control) and a similar reduction in calorie intake (32%; P < .001). Fluid ingestion was also reduced by PYY (18% reduction; P < .01). Nausea and fullness were the most common side effects produced by PYY, especially at the highest dose. Furthermore, subjects experienced less hunger and early fullness in the premeal period during PYY3–36 infusion at the highest dose (P < .05). Conclusions: This study shows that intravenous infusions of PYY3–36 decrease spontaneous food intake; the inhibition is, however, only significant at pharmacologic plasma concentrations. Whether PYY3–36 has a physiologic role in the regulation of satiety in humans remains to be defined. Background & Aims: Studies in animals and humans suggest a role for peptide YY (PYY3–36) in regulating satiety. The physiologic role of PYY3–36, however, has not been investigated in detail. Methods: The present study was designed to examine PYY release in response to 2 meals differing in their calorie content and to relate the plasma levels to those obtained after exogenous infusion. In a second step, the effect of graded intravenous doses (0, 0.2, 0.4, and 0.8 pmol · kg−1 · min−1) of synthetic human PYY3–36 on food intake was investigated in healthy male volunteers in a double-blind, placebo-controlled fashion. Results: Plasma PYY concentrations increased in response to food intake reflecting the size of the calorie load. Graded PYY3–36 infusions resulted in a dose-dependent reduction in food intake (maximal inhibition, 35%; P < .001 vs control) and a similar reduction in calorie intake (32%; P < .001). Fluid ingestion was also reduced by PYY (18% reduction; P < .01). Nausea and fullness were the most common side effects produced by PYY, especially at the highest dose. Furthermore, subjects experienced less hunger and early fullness in the premeal period during PYY3–36 infusion at the highest dose (P < .05). Conclusions: This study shows that intravenous infusions of PYY3–36 decrease spontaneous food intake; the inhibition is, however, only significant at pharmacologic plasma concentrations. Whether PYY3–36 has a physiologic role in the regulation of satiety in humans remains to be defined. Several peptides synthesized and secreted within the gastrointestinal tract are known to modulate eating behavior, such as cholecystokinin, GLP-1, ghrelin, and peptide YY (PYY).1Woods S.C. Gibbs J. The regulation of food intake by peptides.Ann N Y Acad Sci. 1989; 575: 236-243Crossref PubMed Scopus (34) Google Scholar, 2Woods S.C. Gastrointestinal satiety signals I. An overview of gastrointestinal signals that influence food intake.Am J Physiol Gastrointest Liver Physiol. 2004; 286: G7-G13Crossref PubMed Scopus (263) Google Scholar, 3Stanley S. Wynne K. Bloom S. Gastrointestinal satiety signals III. Glucagon-like peptide 1, oxyntomodulin, peptide YY, and pancreatic polypeptide.Am J Physiol Gastrointest Liver Physiol. 2004; 286: G693-G697Crossref PubMed Scopus (103) Google Scholar These peptides respond to nutrients within the gut and interact with specific receptors to modulate appetite.4Strader A.D. Woods S.C. Gastrointestinal hormones and food intake.Gastroenterology. 2005; 128: 175-191Abstract Full Text Full Text PDF PubMed Scopus (370) Google Scholar PYY is one of these gut-derived hormones. Like proglucagon-derived peptides, PYY is synthesized and released from endocrine L cells from the distal gut in response to food consumption.5Adrian T.E. Ferri G.L. Bacarese-Hamilton A.J. Fuessl H.S. Polak J.M. Bloom S.R. Human distribution and release of a putative new gut hormone, peptide YY.Gastroenterology. 1985; 89: 1070-1077Abstract Full Text PDF PubMed Scopus (938) Google Scholar, 6Adrian T.E. Savage A.P. Bacarese-Hamilton A.J. Wolfe K. Besterman H.S. Bloom S.R. Peptide YY abnormalities in gastrointestinal diseases.Gastroenterology. 1986; 90: 379-384Abstract PubMed Google Scholar Fat is a strong stimulus for PYY release, whereas intravenously applied lipids have no effect on circulating PYY concentrations. PYY is converted into PYY3–36 by the enzyme dipeptidyl peptidase IV.7Batterham R.L. Bloom S.R. The gut peptide YY regulates appetite.Ann N Y Acad Sci. 2003; 994: 162-168Crossref PubMed Scopus (259) Google Scholar Receptors that mediate the effects of PYY belong to the neuropeptide Y receptor family and include Y1, Y2, Y3, Y4, and Y5.7Batterham R.L. Bloom S.R. The gut peptide YY regulates appetite.Ann N Y Acad Sci. 2003; 994: 162-168Crossref PubMed Scopus (259) Google Scholar Once PYY3–36 is formed, it binds with high affinity to the Y2 receptor. Recently, the effect of the truncated form of PYY, PYY3–36, on appetite and food intake has been reported.8Batterham R.L. Cohen M.A. Ellis S.M. La Roux C.W. Withers D.J. Frost G.S. Ghatei M.A. Bloom S.R. Inhibition of food intake in obese subjects by peptide YY3-36.N Engl J Med. 2003; 349: 941-948Crossref PubMed Scopus (1350) Google Scholar, 9Batterham R.L. Cowley M.A. Small C.J. Herzog H. Cohen M.A. Dakin C.L. Wren A.M. Brynes A.E. Low M.J. Ghatei M.A. Cone R.D. Bloom S.R. Gut hormone PYY(3-36) physiologically inhibits food intake.Nature. 2002; 418: 650-654Crossref PubMed Scopus (1904) Google Scholar Intravenous infusion of a single dose of PYY3–36 reduced appetite and food consumption by >30% in lean and obese subjects.8Batterham R.L. Cohen M.A. Ellis S.M. La Roux C.W. Withers D.J. Frost G.S. Ghatei M.A. Bloom S.R. Inhibition of food intake in obese subjects by peptide YY3-36.N Engl J Med. 2003; 349: 941-948Crossref PubMed Scopus (1350) Google Scholar The investigators also reported that PYY3–36, when injected into rodents, dampened appetite for 12 hours or more.9Batterham R.L. Cowley M.A. Small C.J. Herzog H. Cohen M.A. Dakin C.L. Wren A.M. Brynes A.E. Low M.J. Ghatei M.A. Cone R.D. Bloom S.R. Gut hormone PYY(3-36) physiologically inhibits food intake.Nature. 2002; 418: 650-654Crossref PubMed Scopus (1904) Google Scholar The animal results were recently questioned, because several groups were unable to reproduce these effects.10Gura T. Labs fail to reproduce protein’s appetite-suppressing effects.Science. 2004; 305: 158-159Crossref PubMed Scopus (9) Google Scholar A dose-response curve to increasing amounts of PYY3–36 on food intake in humans has, however, not been investigated before. To more fully characterize the potential appetite-reducing effects of PYY3–36, the present study was designed to investigate the effects of graded intravenous infusions of synthetic human PYY3–36 on food intake, meal duration, and satiety and fullness feelings in healthy male subjects. The plasma concentrations achieved after exogenous infusion were then compared with levels obtained after meal intake to test whether the appetite-inhibiting effects occurred at physiologic plasma concentrations. Twenty-eight healthy subjects aged 23.6 ± 0.5 years participated in the study. The weight of all subjects was within the normal range considering their age, sex, and height (mean body mass index, 22.6 ± 0.4 kg/m2; range, 19.7–24.8 kg/m2). Each subject gave written informed consent for the study. The protocols were approved by the Human Ethical Research Committee of the University Hospital of Basel. Before acceptance, each participant was required to complete a medical interview, undergo a full physical examination, and participate in an initial laboratory screening. None of the subjects were taking any medication or had a history of food allergies or dietary restrictions. Fasting and postprandial blood samples were taken from 12 healthy subjects aged 20–25 years. On different days and in random order, subjects had blood samples taken after 2 different test meal stimuli: a light lunch (500 kcal) or a large lunch (1500 kcal). The meals were identical in their composition but differed in their calorie content: orange juice as an appetizer (430 kcal/L), ham sandwiches (68 g bread, 10 or 20 g butter, 25 g ham; 284 or 357 kcal per sandwich), and chocolate pudding (133 kcal per 100 g). Details of the meals are given in Table 1. In each case, the subjects had fasted for at least 6 hours before sampling.Table 1Composition of the Test Meals (Light Lunch Containing 500 kcal and Large Lunch Containing 1500 kcal)NutrientsMeal (500 kcal)Meal (1500 kcal)Weight (g)Energy (kcal)Weight (g)Energy (kcal)Ham sandwich White bread68181204542 Ham25317593 Butter107360438 Total kcal2841073Chocolate pudding90120200267Orange juice20086300129 Open table in a new tab Four treatments, separated by at least 7 days, were performed in 16 male subjects. The treatments were identical in design (Figure 1) except for the intravenous infusion (isotonic saline as placebo control or 1 dose of PYY3–36); the order of the experiments was randomized. An identical standard meal was presented to the subjects on each occasion. The meal consisted of orange juice as an appetizer (430 kcal/L), ham sandwiches (68 g bread, 10 g butter, 25 g ham; 284 kcal per sandwich) and more orange juice and chocolate pudding (133 kcal per 100 g), and coffee with cream and sugar (coffee could be sweetened if desired; therefore, both cream and sugar were optional: 12 g cream = 20 kcal; 4.5 sugar = 18 kcal). No additional food or fluid was allowed during the study. At the end of the experiment, the amount of food eaten and the amount of fluid ingested was measured by absolute weight from which total calorie intake (food and fluid intake) was calculated. Each subject was free to eat and drink as much as he wished, but the order of food intake had to follow the above schedule. To reduce the participants’ awareness of the amount of food being provided, food was served in excess. On the day of the experiment, each subject ate breakfast if this was his normal custom, but no snacks were allowed after 8 am. At 12 pm, an intravenous infusion of saline or 1 dose of synthetic PYY3–36 (0.2, 0.4, or 0.8 pmol · kg−1 · min−1, dissolved in isotonic saline containing 0.1% human serum albumin) was started and continued for the duration of each test. Infusions were delivered by ambulatory infusion pumps through a Teflon catheter inserted into a forearm vein. Participants were able to sit, eat, stand, and walk comfortably while receiving infusions. At 60 minutes after the start of the respective infusion, the test meal was presented and each participant was invited to eat and drink as much as he liked. Beginning at 12 pm, the subjects scored their subjective feelings of hunger and fullness at 15-minute intervals throughout the experiments using a visual analogue scale of 0–10 and indicated the scores on a questionnaire. The scales and scores were designed as previously described.11Gutzwiller J.P. Degen L. Matzinger D. Prestin S. Beglinger C. Interaction between GLP-1 and CCK-33 in inhibiting food intake and appetite in men.Am J Physiol Regul Integr Comp Physiol. 2004; 287: R562-R567Crossref PubMed Scopus (78) Google Scholar, 12Gutzwiller J.P. Drewe J. Goke B. Schmidt H. Rohrer B. Lareida J. Beglinger C. Glucagon-like peptide-1 promotes satiety and reduces food intake in patients with diabetes mellitus type 2.Am J Physiol. 1999; 276: R1541-R1544PubMed Google Scholar, 13Gutzwiller J.P. Goke B. Drewe J. Hildebrand P. Ketterer S. Handschin D. Winterhalder R. Conen D. Beglinger C. Glucagon-like peptide-1 a potent regulator of food intake in humans.Gut. 1999; 44: 81-86Crossref PubMed Scopus (500) Google Scholar For example, a score of 0 for hunger indicated the subject was not hungry at all, 2 indicated slightly hungry, 5 indicated moderately hungry, 8 indicated very hungry, and 10 indicated absolutely ravenous. The quantity of food eaten and volume of fluid drunk were measured. The time for each subject to complete his meal was also measured. From these observations, the average rate of food and fluid intake and the calorie intake could be calculated. In the premeal period and after eating, blood was drawn in regular intervals in EDTA tubes containing aprotinin (500 KIU/mL blood) for determination of hormone levels. Adverse effects were assessed by the attending physician through close observation of each subject; in addition, each participant was questioned after each experiment and after he had completed all tests whether he had experienced any adverse effects. The PYY3–36 infusions were prepared from a freeze-dried synthetic powder, PYY3–36, purchased from Bachem (Bubendorf, Switzerland). The peptide was dissolved in isotonic saline containing 0.5% human serum albumin and prepared under aseptic conditions by the hospital pharmacy of the University of Basel. Aliquots of 50 μg/5 mL were stored at −20°C. Infusion solutions were prepared by diluting appropriate amounts of PYY3–36 with saline containing 0.1% human serum albumin. Control solutions contained albumin in saline alone; they were indistinguishable in appearance from PYY3–36 infusions. The person in charge of the experiments was unaware of the respective treatment, thereby making it possible to deliver treatments in a double-blind fashion. Samples were collected on ice with tubes containing aprotinin at a final concentration of 500 KIU/mL of blood; they were processed as quickly as possible and kept on ice to retard the breakdown of PYY. PYY was measured with a commercially available kit (Linco Research Inc, St Charles, MO). The antibody, raised in guinea pigs, displays 100% cross-reactivity with human PYY1–36 and human PYY3–36 but no cross-reactivity with human pancreatic polypeptide, neuropeptide Y, and unrelated peptides such as leptin and ghrelin. 125I-PYY was used as a label; the labeled peptide was purified by high-performance liquid chromatography (sp act, 302 μCi/μg). The lowest level of PYY that can be detected by this assay is 10 pg/mL when using a 100-μL plasma sample size. Ghrelin was measured using a commercially available kit (Linco Research Inc). Data are presented as mean ± SEM unless stated otherwise. The amount of food eaten and the amount of fluid drunk, the corresponding energy intake, and the duration of meal consumption were compared among the 4 treatments by one-way analysis of variance using the general linear model procedure of the SPSS software package (SPSS Inc, Chicago, IL). In the event of significant differences, analysis of variance was followed by the Dunnett multicomparison test for pairwise comparisons. The same statistical procedure was used to analyze the results of PYY3–36–induced changes in plasma hormone concentrations using area-under-the-curve analysis. Scores for hunger and fullness were compared at the different time points before and after the meal among the different treatments using multiple paired t tests with Bonferroni correction. The mean fasting plasma PYY concentration was 126 ± 6 pg/mL in 12 healthy subjects. After ingestion of the light lunch, a small, albeit significant (P < .05) increase in plasma PYY concentration was observed (Figure 2). After ingestion of the large lunch, a marked and sustained increase in PYY levels was seen; the size of the postprandial PYY response clearly reflected the calorie load of the meal. The area under the curve of the postprandial PYY responses to the 2 meals is shown in Figure 3.Figure 3Area under the curve over 120 minutes of PYY measured in plasma (pg/mL) in response to 2 different meals or to graded doses of intravenous PYY3–36 or placebo. The PYY responses expressed as area under the curve over 120 minutes were significantly higher after exogenous infusion compared with meal ingestion (P < .05–.001). Data are expressed as mean ± SEM.View Large Image Figure ViewerDownload Hi-res image Download (PPT) Intravenous infusion of graded doses of synthetic human PYY3–36 dose-dependently reduced the amount of food eaten and the amount of calorie consumption (P < .001 and P < .01, respectively; Table 2). The maximal reduction in food consumption with the highest dose of PYY3–36 (0.8 pmol · kg−1 · min−1) amounted to 35%, resulting in a decrease in calorie intake of 32% (P < .001; Table 2). Fluid ingestion was also reduced by PYY3–36 (18% reduction; P < .01). Meal durations during PYY3–36 infusions were also dose-dependently decreased compared with those with saline infusions and reached statistical significance at the highest dose (P < .05).Table 2Effect of Graded Doses of Human PYY3–36 or Saline (Control) on Eating Behavior in 16 Healthy Male SubjectsTreatmentControlPYY3–36 (pmol·kg−1·min−1)0.20.40.8Food quantity (g)587 ± 36531 ± 35aP < .05.516 ± 40aP < .05.384 ± 34bP < .001.Calorie intake (kcal)1627 ± 971520 ± 951451 ± 101aP < .05.1107 ± 84bP < .001.Meal duration (min)38 ± 335 ± 334 ± 3aP < .05.30 ± 3aP < .05.Fluid intake (mL)708 ± 57748 ± 52689 ± 48aP < .05.584 ± 45cP < .01 vs control.NOTE. Data are expressed as mean ± SEM.a P < .05.b P < .001.c P < .01 vs control. Open table in a new tab NOTE. Data are expressed as mean ± SEM. No statistical differences were observed for hunger and fullness scores with the 2 lower doses of treatment, neither in the premeal period nor after meal intake (Figure 4). The highest dose of PYY reduced feelings of hunger in the premeal period (change in hunger scores from baseline [−60 minutes] to beginning of meal intake [0 minutes]: 1.6 ± 0.3 for PYY vs 0.7 ± 0.3 for saline control; P < .05). In the double-blind part of the study, plasma PYY levels remained at baseline concentrations with saline (placebo) infusion in the premeal period; however, after meal intake, a significant (P < .05) increase in plasma PYY concentrations was observed. In contrast, graded doses of exogenous PYY3–36 produced dose-dependent increases in plasma PYY3–36 concentrations (Figure 5). With increasing doses of PYY3–36, meal intake did not lead to an additional incremental increase in plasma PYY levels above those produced by the infusions. An excellent correlation (r = 0.999; P < .001) was obtained between the infused dose and the measured plasma concentrations (Figure 6). The PYY concentrations observed after the lowest dose of peptide infusion produced plasma levels within the postprandial range; they can therefore be considered physiologic concentrations. The higher 2 doses of exogenous PYY3–36 produced plasma levels that are clearly above the postprandial range; we infer from these data that they are pharmacologic rather than physiologic plasma concentrations.Figure 6Correlation (r = 0.999; P < .001) between graded doses of exogenous human PYY3–36 and plasma PYY concentrations (expressed as area under the curve). Data are expressed as mean ± SEM.View Large Image Figure ViewerDownload Hi-res image Download (PPT) Ghrelin levels increased throughout the premeal period on the day the subjects received saline and then decreased postprandially 30 minutes after the meal began (Figure 7). The lower 2 doses of PYY3–36 did not significantly change fasting and postprandial ghrelin concentrations (data not shown). The highest dose of PYY infusion, however, significantly (P < .05) decreased ghrelin levels during the premeal period and reduced the early increase after the beginning of meal intake (see Figure 7). The area under the curve for ghrelin was 97,677 ± 4637 pmol per 120 min/mL on the day subjects received saline and 84,587 ± 5136 pmol per 120 min/mL on the day they received the highest dose of PYY3–36 (P < .05). The most common adverse events after intravenous administration of PYY3–36 were nausea, fullness, abdominal discomfort, and sweating (Table 3). The adverse events were clearly dose dependent and largely occurred with the highest dose of PYY3–36. In 1 subject, the infusion had to be stopped prematurely (highest dose of PYY3–36) because of vomiting. The plasma concentrations leading to nausea were in the order of >300 pg/mL (total PYY). This indicates a relatively narrow therapeutic range. All adverse events disappeared spontaneously within a few minutes without any specific treatment or after stopping the infusion.Table 3Number of Adverse Events in Response to Graded Doses of Human PYY3–36 or Saline (Control) in 16 Healthy Male SubjectsTreatmentControlPYY3–36 (pmol·kg−1·min−1)0.20.40.8Nausea0024Vomiting0001Abdominal discomfort0026Fullness0024Sweating0110 Open table in a new tab In animals, expression of Y2 receptors has been found in the hypothalamus, medulla, and pons but not in the cortex.14Corp E.S. Greco B. Powers J.B. Marin Bivens C.L. Wade G.N. Neuropeptide Y inhibits estrous behavior and stimulates feeding via separate receptors in Syrian hamsters.Am J Physiol Regul Integr Comp Physiol. 2001; 280: R1061-R1068PubMed Google Scholar, 15Inui A. Okita M. Miura M. Hirosue Y. Nakajima M. Inoue T. Oya M. Baba S. Characterization of the receptors for peptide-YY and avian pancreatic polypeptide in chicken and pig brains.Endocrinology. 1990; 127: 934-941Crossref PubMed Scopus (17) Google Scholar, 16Danger J.M. Tonon M.C. Jenks B.G. Saint-Pierre S. Martel J.C. Fasolo A. Breton B. Quirion R. Pelletier G. Vaudry H. Neuropeptide Y localization in the central nervous system and neuroendocrine functions.Fundam Clin Pharmacol. 1990; 4: 307-340Crossref PubMed Scopus (111) Google Scholar Furthermore, PYY immunoreactivity has been reported in the central nervous system, hypothalamus, medulla, and pons.15Inui A. Okita M. Miura M. Hirosue Y. Nakajima M. Inoue T. Oya M. Baba S. Characterization of the receptors for peptide-YY and avian pancreatic polypeptide in chicken and pig brains.Endocrinology. 1990; 127: 934-941Crossref PubMed Scopus (17) Google Scholar, 16Danger J.M. Tonon M.C. Jenks B.G. Saint-Pierre S. Martel J.C. Fasolo A. Breton B. Quirion R. Pelletier G. Vaudry H. Neuropeptide Y localization in the central nervous system and neuroendocrine functions.Fundam Clin Pharmacol. 1990; 4: 307-340Crossref PubMed Scopus (111) Google Scholar, 17Parker S.L. Carroll B.L. Kalra S.P. St-Pierre S. Fournier A. Crowley W.R. Neuropeptide Y Y2 receptors in hypothalamic neuroendocrine areas are up-regulated by estradiol and decreased by progesterone cotreatment in the ovariectomized rat.Endocrinology. 1996; 137: 2896-2900Crossref PubMed Google Scholar With the presence of Y2 receptors at sites where administration of exogenous PYY3–36 appears to cause satiety, one is faced with attempting to determine if the satiety effect of PYY3–36 is physiologic and, if so, whether it is a major satiety factor. Recent data obtained in rodents and humans have provided experimental evidence that PYY3–36 can function as a mediator of food-induced satiety. Intra-arcuate injection of PYY3–36 reduced food intake in mice. In addition, the effects of PYY3–36 were abolished in Y2−/ − mice. Intraperitoneal PYY3–36 reduced dark-phase and fasting-induced feeding in rodents.9Batterham R.L. Cowley M.A. Small C.J. Herzog H. Cohen M.A. Dakin C.L. Wren A.M. Brynes A.E. Low M.J. Ghatei M.A. Cone R.D. Bloom S.R. Gut hormone PYY(3-36) physiologically inhibits food intake.Nature. 2002; 418: 650-654Crossref PubMed Scopus (1904) Google Scholar Repeated PYY3–36 administration reduced food intake and body weight gain. Finally, similar anorectic effects were seen in humans.7Batterham R.L. Bloom S.R. The gut peptide YY regulates appetite.Ann N Y Acad Sci. 2003; 994: 162-168Crossref PubMed Scopus (259) Google Scholar, 8Batterham R.L. Cohen M.A. Ellis S.M. La Roux C.W. Withers D.J. Frost G.S. Ghatei M.A. Bloom S.R. Inhibition of food intake in obese subjects by peptide YY3-36.N Engl J Med. 2003; 349: 941-948Crossref PubMed Scopus (1350) Google Scholar, 9Batterham R.L. Cowley M.A. Small C.J. Herzog H. Cohen M.A. Dakin C.L. Wren A.M. Brynes A.E. Low M.J. Ghatei M.A. Cone R.D. Bloom S.R. Gut hormone PYY(3-36) physiologically inhibits food intake.Nature. 2002; 418: 650-654Crossref PubMed Scopus (1904) Google Scholar These findings prompted the investigators to suggest that PYY3–36 is a potent physiologic regulator of satiety with a potential for therapeutic application. However, other laboratories were unable to reproduce the results in laboratory animals, causing a controversy on the biologic importance of PYY3–36 as a physiologic satiety factor.10Gura T. Labs fail to reproduce protein’s appetite-suppressing effects.Science. 2004; 305: 158-159Crossref PubMed Scopus (9) Google Scholar A set of criteria has been defined in classic endocrinology for establishing a physiologic endocrine action of a given molecule.18Geary N. Endocrine controls of eating CCK, leptin, and ghrelin.Physiol Behav. 2004; 81: 719-733Crossref PubMed Scopus (119) Google Scholar According to these criteria, a physiologic action of PYY3–36 has not yet been established and urgently requires further research. The purpose of this study was 2-fold. First, we studied the effect of 2 different calorie loads of an identical meal on PYY secretion to define the range of postprandial plasma PYY concentrations. Second, we constructed a dose-response curve and examined the effect of graded doses of intravenous synthetic human PYY3–36 on eating behavior and satiety in healthy male subjects to define the physiologic dose of the peptide that reproduces the secretion pattern of the endogenous peptide that is associated with changes in food intake. In the following section, we analyze our results according to these criteria. PYY is synthesized and released by the L cells in the distal small intestine.5Adrian T.E. Ferri G.L. Bacarese-Hamilton A.J. Fuessl H.S. Polak J.M. Bloom S.R. Human distribution and release of a putative new gut hormone, peptide YY.Gastroenterology. 1985; 89: 1070-1077Abstract Full Text PDF PubMed Scopus (938) Google Scholar Although the specific stimuli for PYY secretion are unknown, the increases in plasma concentration of PYY after meals and the low concentrations in the fasting state are consistent with a satiety-inducing action. The circadian pattern of PYY secretion has, however, not yet been studied in humans in detail. The results of the present study confirm that only large meals are able to stimulate the release of larger amounts of PYY into the circulation, whereas a 500-kcal meal has minimal effects on postprandial hormone concentrations.5Adrian T.E. Ferri G.L. Bacarese-Hamilton A.J. Fuessl H.S. Polak J.M. Bloom S.R. Human distribution and release of a putative new gut hormone, peptide YY.Gastroenterology. 1985; 89: 1070-1077Abstract Full Text PDF PubMed Scopus (938) Google Scholar Graded intravenous infusions of PYY3–36 increased plasma PYY concentrations 2- to 5-fold over fasting levels, indicating that only the lowest dose mimicked physiologic PYY levels, whereas the upper 2 doses produced plasma levels that were clearly out of the physiologic range. It has to be noted that after meal intake, 60% of circulating PYY is PYY3–36 and the rest is PYY1–36.19Talsania T. Anini Y. Siu S. Drucker D.J. Brubaker P.L. Peripheral exendin-4 and peptide YY(3-36) synergistically reduce food intake through different mechanisms in mice.Endocrinology. 2005; 146: 3748-3756Crossref PubMed Scopus (268) Google Scholar, 20Halatchev I.G. Ellacott K.L. Fan W. Cone R.D. Peptide YY3-36 inhibits food intake in mice through a melanocortin-4 receptor-independent mechanism.Endocrinology. 2004; 145: 2585-2590Crossref PubMed Scopus (206) Google Scholar The assay system used in the present study recognizes both molecules; therefore, after meal intake, only part of the measured PYY represents the active molecule. In contrast, after exogenous infusion, all measured peptide represents PYY3–36. Thus, the doses of PYY3–36 that induce inhibition of food intake are likely to produce plasma PYY3–36 levels that are even higher than those produced by the 1500-kcal meal. The results of the study clearly show that dose-dependent satiety effects can be induced by peripherally infused PYY3–36 in human subjects; the results support the hypothesis that exogenously administered PYY3–36 can suppress food intake in humans. The lack of a specific PYY3–36 receptor antagonist that could be given to humans prevents us for the moment from deciding whether the effects produced by the exogenous administration of PYY3–36 (as used in this study) are true physiologic effects. Comparison of the plasma concentrations seen after exogenous infusion with the levels seen after a 1500-kcal meal suggests, however, that the significant satiety effects of PYY3–36 were only seen at plasma concentrations, which were above those of a high-calorie meal. Indeed, the pharmacologic nature of the upper 2 doses is indicated by these observations, because a significant inhibitory effect on food parameters was only observed under these experimental conditions. Thus, more work is required to determine if PYY3–36 meets the criterion for a fully coupled physiologic hormonal effect. We infer that the results of this study represent a pharmacologic rather than a physiologic effect of PYY3–36. The early reports from Batterham et al8Batterham R.L. Cohen M.A. Ellis S.M. La Roux C.W. Withers D.J. Frost G.S. Ghatei M.A. Bloom S.R. Inhibition of food intake in obese subjects by peptide YY3-36.N Engl J Med. 2003; 349: 941-948Crossref PubMed Scopus (1350) Google Scholar, 9Batterham R.L. Cowley M.A. Small C.J. Herzog H. Cohen M.A. Dakin C.L. Wren A.M. Brynes A.E. Low M.J. Ghatei M.A. Cone R.D. Bloom S.R. Gut hormone PYY(3-36) physiologically inhibits food intake.Nature. 2002; 418: 650-654Crossref PubMed Scopus (1904) Google Scholar used only 1 dose of peptide to induce satiation in healthy subjects and in obese people; the plasma concentrations observed in these experiments suggest that a pharmacologic dose of PYY3–36 was infused. More importantly, the inhibition of feeding induced with these pharmacologic doses was accompanied by subjective side effects in the present study, whereas the physiologic dose (0.2 pmol · kg−1 · min−1) was insufficient to reduce meal size or calorie intake. The results therefore indicate that under these experimental conditions, PYY3–36 satiation does not meet the criterion for a physiologic hormonal effect. With the present study, an alternative physiologic pathway of PYY3–36 as a satiety hormone has not been excluded. The molecule could act locally within the gut acting on vagal afferents that mediate the satiating effect; at least in rodents, such a local action has been described for cholecystokinin, the classic peptide that produces satiety.1Woods S.C. Gibbs J. The regulation of food intake by peptides.Ann N Y Acad Sci. 1989; 575: 236-243Crossref PubMed Scopus (34) Google Scholar, 2Woods S.C. Gastrointestinal satiety signals I. An overview of gastrointestinal signals that influence food intake.Am J Physiol Gastrointest Liver Physiol. 2004; 286: G7-G13Crossref PubMed Scopus (263) Google Scholar The close proximity of the cholecystokinin-secreting cells in the small intestine to the pyloric site of the crucial receptors for satiation supports this hypothesis.1Woods S.C. Gibbs J. The regulation of food intake by peptides.Ann N Y Acad Sci. 1989; 575: 236-243Crossref PubMed Scopus (34) Google Scholar, 2Woods S.C. Gastrointestinal satiety signals I. An overview of gastrointestinal signals that influence food intake.Am J Physiol Gastrointest Liver Physiol. 2004; 286: G7-G13Crossref PubMed Scopus (263) Google Scholar, 18Geary N. Endocrine controls of eating CCK, leptin, and ghrelin.Physiol Behav. 2004; 81: 719-733Crossref PubMed Scopus (119) Google Scholar In contrast to the cholecystokinin-secreting cells, which are predominantly localized in the upper gastrointestinal tract, PYY-secreting cells are mainly in the terminal ileum and the colon; it remains to be shown whether locally released PYY is sufficient to stimulate neural pathways that mediate the satiating effects. The mechanism by which PYY3–36 inhibits food intake is not clear and could possibly be due to different actions. Is the effect directly mediated by binding to peripheral or central receptors, or is it mediated through stimulation of other satiety factors? The question cannot be answered at the present time because a demonstration of a direct action of PYY3–36 would require experiments with a selective PYY3–36 receptor antagonist specifically blocking endogenous PYY3–36. Is the reduction of food consumption secondary to nonspecific behavioral effects of the treatments (side effects)? Is the effect peripheral or mediated by central receptors? Does PYY3–36 act as a hormone, and does it cross the blood-brain barrier? A direct central mechanism of PYY3–36 rather than a peripheral effect is derived from an experimental model of the blood-brain barrier.21Leslie R.A. McDonald T.J. Robertson H.A. Autoradiographic localization of peptide YY and neuropeptide Y binding sites in the medulla oblongata.Peptides. 1988; 9: 1071-1076Crossref PubMed Scopus (42) Google Scholar, 22Jobst E.E. Enriori P.J. Cowley M.A. The electrophysiology of feeding circuits.Trends Endocrinol Metab. 2004; 15: 488-499Abstract Full Text Full Text PDF PubMed Scopus (119) Google Scholar, 23Nonaka N. Shioda S. Niehoff M.L. Banks W.A. Characterization of blood-brain barrier permeability to PYY3-36 in the mouse.J Pharmacol Exp Ther. 2003; 306: 948-953Crossref PubMed Scopus (148) Google Scholar These data suggest that PYY3–36 is selectively transported through the blood-brain barrier. Does PYY3–36 inhibit food intake by stimulating the release of other peptides that are known to be involved in the regulation? In the present study, we have measured the effect of PYY3–36 on plasma ghrelin concentrations. The results presented in this study confirm that ghrelin levels are decreased in response to high doses of PYY3–36 in the premeal period.10Gura T. Labs fail to reproduce protein’s appetite-suppressing effects.Science. 2004; 305: 158-159Crossref PubMed Scopus (9) Google Scholar Plasma levels of ghrelin increase before meal ingestion and administration of ghrelin increases food intake in humans, suggesting that ghrelin has a role in the regulation of meal initiation.24Cummings D.E. Purnell J.Q. Frayo R.S. Schmidova K. Wisse B.E. Weigle D.S. A preprandial rise in plasma ghrelin levels suggests a role in meal initiation in humans.Diabetes. 2001; 50: 1714-1719Crossref PubMed Scopus (2443) Google Scholar, 25Wren A.M. Seal L.J. Cohen M.A. Brynes A.E. Frost G.S. Murphy K.G. Dhillo W.S. Ghatei M.A. Bloom S.R. Ghrelin enhances appetite and increases food intake in humans.J Clin Endocrinol Metab. 2001; 86: 5992-5995Crossref PubMed Scopus (2163) Google Scholar The suppression of ghrelin levels seen with high doses of PYY suggests an interaction between these 2 regulatory circuits. Whether this interaction is a pharmacologic effect or a true physiologic action remains to be determined. In conclusion, we have shown that graded doses of human PYY3–36 reduce intake of food in nonobese, healthy male subjects. The effect is a pharmacologic rather than a physiologic action of the peptide. The mechanism of action has to be clarified. Further investigation is needed to define a potential physiologic role of PYY3–36 in the control of human food intake. Whether the peptide can emerge as a powerful antiobesity drug remains to be seen; the present results suggest that the therapeutic window is rather narrow. The authors thank the team of the Clinical Research Center and Gerdien Gamboni for expert technical assistance.