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Type: Journal article
Title: Effects of intraduodenal infusion of L-tryptophan on ad libitum eating, antropyloroduodenal motility, glycemia, insulinemia, and gut peptide secretion in healthy men
Author: Steinert, R.
Luscombe-Marsh, N.
Little, T.
Standfield, S.
Otto, B.
Horowitz, M.
Feinle-Bisset, C.
Citation: Journal of Clinical Endocrinology and Metabolism, 2014; 99(9):3275-3284
Publisher: Endocrine Society
Issue Date: 2014
ISSN: 0021-972X
Statement of
Robert E. Steinert, Natalie D. Luscombe-Marsh, Tanya J. Little, Scott Standfield, Bärbel Otto, Michael Horowitz, and Christine Feinle-Bisset
Abstract: CONTEXT: 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). MAIN OUTCOME MEASURES: 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.
Keywords: Duodenum
Rights: © 2014 by the Endocrine Society
DOI: 10.1210/jc.2014-1943
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