title: Effect of GLP-1 and GIP on C-peptide secretion after glucagon or mixed meal tests: Significance in assessing B-cell function in diabetes.
abstract: The aim of the study was to investigate the different B-cell responses after a glucagon stimulation test (GST) versus mixed meal tolerance test (MMTT).
  
  
  
  We conducted GST and MMTT in 10 healthy people (aged 25-40 years) and measured C-peptide, gastric inhibitory peptide (GIP) and glucagon-like peptide-1 (GLP-1) at different time points after the administration of 1 mg i.v. glucagon for GST or a liquid mixed meal for MMTT.
  
  
  
  The GST stimulated C-peptide showed a mean increase of 147.1%, whereas the mean increase of MMTT stimulated C-peptide was 99.82% (Δincrease = 47.2%). Maximum C-peptide level reached with the MMTT was greater than that obtained with the GST (C-pept max MMTT = 2.35 nmol/L vs C-pep max GST = 1.9 nmol/L). A positive and linear correlation was found between the GST incremental area under the curve C-peptide and the MMTT incremental area under the curve C-peptide (r = 0.618, P = .05). After GST, there was no increment of GIP and glucagon like peptide-1 levels compared to baseline levels. A positive and linear correlation between GIP and C-peptide levels was observed only for the MMTT (r = 0.922, P = .008) indicating that in the GST, the C-peptide response is independent of the incretin axis response.
  
  
  
  Although the 2 stimulation tests may elicit a similar response in C-peptide secretion, B-cell response to MMTT depends on a functionally normal incretin axis. These results may have implications when investigating the B-cell response in people with diabetes and for studies in which stimulated C-peptide secretion is used as primary or secondary outcome for response to therapy.
authors.affiliation: Unit of Endocrinology and Diabetes, University Campus Bio Medico of Rome, Rome, Italy.
authors.forename: C
authors.initials: C
authors.lastname: Guglielmi
authors.affiliation: Unit of Endocrinology and Diabetes, University Campus Bio Medico of Rome, Rome, Italy.
authors.forename: R
authors.initials: R
authors.lastname: Del Toro
authors.affiliation: Unit of Endocrinology and Diabetes, University Campus Bio Medico of Rome, Rome, Italy.
authors.forename: A
authors.initials: A
authors.lastname: Lauria
authors.affiliation: Unit of Endocrinology and Diabetes, University Campus Bio Medico of Rome, Rome, Italy.
authors.forename: A R
authors.initials: AR
authors.lastname: Maurizi
authors.affiliation: Unit of Endocrinology and Diabetes, University Campus Bio Medico of Rome, Rome, Italy.
authors.forename: S
authors.initials: S
authors.lastname: Fallucca
authors.affiliation: Unit of Endocrinology and Diabetes, University Campus Bio Medico of Rome, Rome, Italy.
authors.forename: A
authors.initials: A
authors.lastname: Cappelli
authors.affiliation: Clinical Pathology and Microbiology Laboratory, University Campus Bio Medico of Rome, Rome, Italy.
authors.forename: S
authors.initials: S
authors.lastname: Angeletti
authors.affiliation: The Biostatistics Center, George Washington University, Rockville, Maryland, USA.
authors.forename: J M
authors.initials: JM
authors.lastname: Lachin
authors.affiliation: Unit of Endocrinology and Diabetes, University Campus Bio Medico of Rome, Rome, Italy.|Centre of Diabetes, Blizard Institute, Queen Mary University of London, Barts and The London School of Medicine, London, UK.
authors.forename: P
authors.identifier: 0000-0001-5090-636X
authors.initials: P
authors.lastname: Pozzilli
mesh_terms: D000328:Adult; D002096:C-Peptide / Q000378:metabolism*; D018592:Cross-Over Studies; D003924:Diabetes Mellitus, Type 2 / Q000175:diagnosis* / Q000503:physiopathology; D003940:Diagnostic Techniques, Endocrine; D004435:Eating / Q000502:physiology; D005260:Female; D005749:Gastric Inhibitory Polypeptide / Q000494:pharmacology*; D005934:Glucagon / Q000008:administration & dosage*; D052216:Glucagon-Like Peptide 1 / Q000494:pharmacology*; D006801:Humans; D050417:Insulin-Secreting Cells / Q000187:drug effects* / Q000502:physiology; D008297:Male; D062407:Meals; D013268:Stimulation, Chemical
chemical_list: D002096:C-Peptide; D005749:Gastric Inhibitory Polypeptide; D052216:Glucagon-Like Peptide 1; D005934:Glucagon
keywords: B-cell function; C-peptide; diabetes; glucagon stimulation test; incretin axis; mixed meal tolerance test