title: Secretion of the incretin hormones glucagon-like peptide-1 and gastric inhibitory polypeptide correlates with insulin secretion in normal man throughout the day.
abstract: BACKGROUND
  The insulinotropic hormones gastric inhibitory polypeptide (GIP) and glucagon-like peptide-1 (GLP-1), secreted from the K-cells of the upper small intestine and from the L-cells of the lower small intestine, respectively, are thought to be responsible for intestinal stimulation of insulin secretion. If true, their plasma concentrations should parallel the meal-related diurnal changes in plasma insulin concentrations.
  
  
  METHODS
  Using COOH-terminal assays, thought to reflect accurately their rates of secretion, we measured circulating levels of GIP and GLP-1 in six normal subjects for 15 h of a day, during which they ate three mixed meals.
  
  
  RESULTS
  Both GIP and GLP-1 concentrations increased significantly and in parallel with insulin in response to all three meals. The plasma insulin concentrations correlated significantly with both GIP and GLP-1 values throughout the study period (correlation coefficients, 0.49 +/- 0.07 and 0.56 +/- 0.05; p < 0.001).
  
  
  CONCLUSIONS
  These results support the notion that GLP-1 and GIP are important incretin hormones.
authors.affiliation: Dept. of Medical Anatomy, Panum Institute, University of Copenhagen, Denmark.
authors.forename: C
authors.initials: C
authors.lastname: Orskov
authors.forename: A
authors.initials: A
authors.lastname: Wettergren
authors.forename: J J
authors.initials: JJ
authors.lastname: Holst
mesh_terms: D000328:Adult; D002940:Circadian Rhythm; D005260:Female; D005749:Gastric Inhibitory Polypeptide / Q000378:metabolism*; D005768:Gastrointestinal Hormones / Q000378:metabolism*; D005934:Glucagon / Q000378:metabolism*; D052216:Glucagon-Like Peptide 1; D004763:Glucagon-Like Peptides; D006801:Humans; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007421:Intestine, Small / Q000378:metabolism; D008297:Male; D010446:Peptide Fragments / Q000378:metabolism*
chemical_list: D005768:Gastrointestinal Hormones; D007328:Insulin; D010446:Peptide Fragments; C055453:glucagon-like peptide 1 (7-36)amide; D005749:Gastric Inhibitory Polypeptide; D004763:Glucagon-Like Peptides; D052216:Glucagon-Like Peptide 1; D005934:Glucagon