title: Altered pattern of the incretin effect as assessed by modelling  in individuals with glucose tolerance ranging from normal  to diabetic.
abstract: OBJECTIVE
  Oral glucose elicits a higher insulin secretory response than intravenous glucose at matched glucose concentrations. This potentiation, known as the incretin effect, is typically expressed as the difference between the total insulin response to oral vs intravenous glucose. This approach does not describe the dynamics of insulin secretion potentiation. We developed a model for the simultaneous analysis of oral and isoglycaemic intravenous glucose responses to dissect the impact of hyperglycaemia and incretin effect on insulin secretion and beta cell function.
  
  
  METHODS
  Fifty individuals (23 with normal glucose tolerance [NGT], 17 with impaired glucose tolerance [IGT] and ten with type 2 diabetes) received an OGTT and an isoglycaemic test with measurement of plasma glucose, insulin, C-peptide, glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP). Our model featured an incretin potentiation factor (PINCR) for the dose–response function relating insulin secretion to glucose concentration, and an effect on early secretion (rate sensitivity).
  
  
  RESULTS
  In NGT, PINCR rapidly increased and remained sustained during the whole OGTT (mean PINCR>1, p<0.009). The increase was transient in IGT and virtually absent in diabetes. Mean PINCR was significantly but loosely correlated with GLP-1 AUC (r=0.49, p<0.006), while the relationship was not significant for GIP. An incretin effect on rate sensitivity was present in all groups (p<0.002).
  
  
  CONCLUSIONS
  The onset of the incretin effect is rapid and sustained in NGT, transient in IGT and virtually absent in diabetes. The profiles of the incretin effect are poorly related to those of the incretin hormones.
authors.forename: Andrea
authors.initials: A
authors.lastname: Tura
authors.forename: Elza
authors.initials: E
authors.lastname: Muscelli
authors.forename: Amalia
authors.initials: A
authors.lastname: Gastaldelli
authors.forename: Ele
authors.initials: E
authors.lastname: Ferrannini
authors.forename: Andrea
authors.initials: A
authors.lastname: Mari
mesh_terms: D000328:Adult; D001786:Blood Glucose / Q000378:metabolism; D002096:C-Peptide / Q000097:blood; D003924:Diabetes Mellitus, Type 2 / Q000097:blood / Q000378:metabolism*; D005260:Female; D005749:Gastric Inhibitory Polypeptide / Q000097:blood; D052216:Glucagon-Like Peptide 1 / Q000097:blood; D018149:Glucose Intolerance; D005951:Glucose Tolerance Test; D006801:Humans; D054795:Incretins / Q000378:metabolism*; D007328:Insulin / Q000097:blood; D008297:Male; D008875:Middle Aged; D008962:Models, Theoretical
chemical_list: D001786:Blood Glucose; D002096:C-Peptide; D054795:Incretins; D007328:Insulin; D005749:Gastric Inhibitory Polypeptide; D052216:Glucagon-Like Peptide 1