Effects of intragastric administration of L-tryptophan on the glycaemic response to a nutrient drink in men with type 2 diabetes — impacts on gastric emptying, glucoregulatory hormones and glucose absorption

• Published in: Nutrition & diabetes 2021-01, Vol.11 (1), p.3-9, Article 3
• Main Authors: Hajishafiee, Maryam, Elovaris, Rachel A., Jones, Karen L., Heilbronn, Leonie K., Horowitz, Michael, Poppitt, Sally D., Feinle-Bisset, Christine
• Format: Article
• Language: English
• Subjects: 3-O-Methylglucose - blood; 631/443/319/1642/137/773; 692/163/2743/137/773; Aged; Beverages; Blood Glucose - drug effects; C-Peptide - blood; Clinical Nutrition; Diabetes; Diabetes Mellitus, Type 2 - blood; Diabetes Mellitus, Type 2 - drug therapy; Double-Blind Method; Drug Administration Routes; Epidemiology; Gastric Emptying - drug effects; Glucagon; Glucagon - blood; Glucose; Glucose - metabolism; Humans; Insulin - blood; Internal Medicine; Intestinal Absorption; Male; Medicine; Medicine & Public Health; Metabolic Diseases; Middle Aged; Nutrients; Obesity - drug therapy; Peptides; Postprandial Period; Tryptophan - administration & dosage
• ISSN: 2044-4052; 2044-4052
• DOI: 10.1038/s41387-020-00146-9

Background The rate of gastric emptying and glucoregulatory hormones are key determinants of postprandial glycaemia. Intragastric administration of L-tryptophan slows gastric emptying and reduces the glycaemic response to a nutrient drink in lean individuals and those with obesity. We investigated whether tryptophan decreases postprandial glycaemia and slows gastric emptying in type 2 diabetes (T2D). Methods Twelve men with T2D (age: 63 ± 2 years, HbA1c: 49.7 ± 2.5 mmol/mol, BMI: 30 ± 1 kg/m 2 ) received, on three separate occasions, 3 g (‘Trp-3’) or 1.5 g (‘Trp-1.5’) tryptophan, or control (0.9% saline), intragastrically, in randomised, double-blind fashion, 30 min before a mixed-nutrient drink (500 kcal, 74 g carbohydrates), containing 3 g 3-O-methyl-D-glucose (3-OMG) to assess glucose absorption. Venous blood samples were obtained at baseline, after tryptophan, and for 2 h post-drink for measurements of plasma glucose, C-peptide, glucagon and 3-OMG. Gastric emptying of the drink was quantified using two-dimensional ultrasound. Results Tryptophan alone stimulated C-peptide ( P  = 0.002) and glucagon ( P  = 0.04), but did not affect fasting glucose. In response to the drink, Trp-3 lowered plasma glucose from t  = 15–30 min and from t  = 30–45 min compared with control and Trp-1.5, respectively (both P