title: Effects of intraduodenal infusion of L-tryptophan on ad libitum eating, antropyloroduodenal motility, glycemia, insulinemia, and gut peptide secretion in healthy men.
abstract: BACKGROUND
  Changes in gut motor and hormonal function contribute to the eating-inhibitory and glucose-lowering effects of protein. The effect of amino acids, the digestive products of protein, on gastrointestinal function, eating, and glycemia has not been investigated comprehensively.
  
  
  OBJECTIVE
  We tested the hypothesis that L-tryptophan (L-Trp) stimulates gastrointestinal motor and hormonal functions, inhibits eating, and modulates glycemia. Design, Settings, Participants, and Intervention: Ten healthy, normal-weight men were studied in randomized, double-blind fashion, each receiving a 90-minute intraduodenal infusion of L-Trp at 0.075 (total 6.75 kcal) or 0.15 (total 13.5 kcal) kcal/min or saline (control).
  
  
  METHODS
  Antropyloroduodenal motility, plasma ghrelin, cholecystokinin, glucagon-like peptide-1, peptide tyrosine tyrosine, insulin, glucagon, blood glucose, and appetite perceptions were measured. Food intake was quantified from a buffet meal after the infusion.
  
  
  RESULTS
  Intraduodenal L-Trp suppressed antral pressures (P < .05) and stimulated pyloric pressures (P < .01) and markedly increased cholecystokinin and glucagon (both P < .001). Glucagon-like peptide-1 and peptide tyrosine tyrosine increased modestly (both P < .001), but there was no effect on total ghrelin. Insulin increased slightly (P < .05) without affecting blood glucose. Plasma L-Trp increased substantially (P < .001). All effects were dose-related and associated with increased fullness and substantially decreased energy intake (P < .001). There was a strong inverse correlation between energy intake and plasma L-Trp (r = -0.70; P < .001).
  
  
  CONCLUSIONS
  Low caloric intraduodenal loads of L-Trp affect gut motor and hormonal function and markedly reduce energy intake. A strong inverse correlation between energy intake and plasma L-Trp suggests that, beyond gut mechanisms, direct effects of circulating L-Trp mediate its eating-inhibitory effect.
authors.affiliation: University of Adelaide, Discipline of Medicine (R.E.S., S.S., M.H., C.F.-B.), Adelaide, SA 5005, Australia; National Health and Medical Research Council, Centre of Research Excellence in Translating Nutritional Science to Good Health (R.E.S., N.D.L.-M., S.S., M.H., C.F.-B.), Adelaide, SA 5005, Australia; Preventative Health National Research Flagship, Commonwealth Scientific and Industrial Research Organisation, Animal, Food and Health Sciences (N.D.L.-M.), Adelaide, SA 5005, Australia; The Boden Institute of Obesity, Nutrition, Exercise, and Eating Disorders (T.J.L.), Sydney Medical School, The University of Sydney, Sydney, NSW 2006, Australia; and Medizinische Klinik (B.O.), Klinikum Innenstadt, University of Munich, 80336 Munich, Germany.
authors.forename: Robert E
authors.initials: RE
authors.lastname: Steinert
authors.forename: Natalie D
authors.initials: ND
authors.lastname: Luscombe-Marsh
authors.forename: Tanya J
authors.initials: TJ
authors.lastname: Little
authors.forename: Scott
authors.initials: S
authors.lastname: Standfield
authors.forename: Bärbel
authors.initials: B
authors.lastname: Otto
authors.forename: Michael
authors.initials: M
authors.lastname: Horowitz
authors.forename: Christine
authors.initials: C
authors.lastname: Feinle-Bisset
mesh_terms: D000293:Adolescent; D000328:Adult; D001067:Appetite Depressants / Q000008:administration & dosage*; D001786:Blood Glucose / Q000187:drug effects*; D002766:Cholecystokinin / Q000097:blood; D004305:Dose-Response Relationship, Drug; D004311:Double-Blind Method; D004386:Duodenum / Q000187:drug effects*; D004435:Eating / Q000187:drug effects; D025461:Feedback, Physiological / Q000502:physiology; D005247:Feeding Behavior / Q000187:drug effects*; D005746:Gastric Emptying / Q000187:drug effects; D005769:Gastrointestinal Motility / Q000187:drug effects; D005934:Glucagon / Q000097:blood; D064368:Healthy Volunteers; D006801:Humans; D007328:Insulin / Q000097:blood*; D008297:Male; D019894:Peptide YY / Q000097:blood; D011706:Pyloric Antrum / Q000187:drug effects; D014364:Tryptophan / Q000008:administration & dosage* / Q000097:blood; D055815:Young Adult
chemical_list: D001067:Appetite Depressants; D001786:Blood Glucose; D007328:Insulin; D019894:Peptide YY; D014364:Tryptophan; D005934:Glucagon; D002766:Cholecystokinin