Effects of the novel (Pro3)GIP antagonist and exendin(9-39)amide on GIP- and GLP-1-induced cyclic AMP generation, insulin secretion and postprandial insulin release in obese diabetic (ob/ob) mice: evidence that GIP is the major physiological incretin

Diabetologia. 2003 Feb;46(2):222-30. doi: 10.1007/s00125-002-1028-x. Epub 2003 Feb 12.

Abstract

Aims/hypothesis: This study examined the biological effects of the GIP receptor antagonist, (Pro3)GIP and the GLP-1 receptor antagonist, exendin(9-39)amide.

Methods: Cyclic AMP production was assessed in Chinese hamster lung fibroblasts transfected with human GIP or GLP-1 receptors, respectively. In vitro insulin release studies were assessed in BRIN-BD11 cells while in vivo insulinotropic and glycaemic responses were measured in obese diabetic ( ob/ ob) mice.

Results: In GIP receptor-transfected fibroblasts, (Pro(3))GIP or exendin(9-39)amide inhibited GIP-stimulated cyclic AMP production with maximal inhibition of 70.0+/-3.5% and 73.5+/-3.2% at 10(-6) mol/l, respectively. In GLP-1 receptor-transfected fibroblasts, exendin(9-39)amide inhibited GLP-1-stimulated cyclic AMP production with maximal inhibition of 60+/-0.7% at 10(-6) mol/l, whereas (Pro(3))GIP had no effect. (Pro(3))GIP specifically inhibited GIP-stimulated insulin release (86%; p<0.001) from clonal BRIN-BD11 cells, but had no effect on GLP-1-stimulated insulin release. In contrast, exendin(9-39)amide inhibited both GIP and GLP-1-stimulated insulin release (57% and 44%, respectively; p<0.001). Administration of (Pro(3))GIP, exendin(9-39)amide or a combination of both peptides (25 nmol/kg body weight, i.p.) to fasted (ob/ob) mice decreased the plasma insulin responses by 42%, 54% and 49%, respectively (p<0.01 to p<0.001). The hyperinsulinaemia of non-fasted (ob/ob) mice was decreased by 19%, 27% and 18% (p<0.05 to p<0.01) by injection of (Pro3)GIP, exendin(9-39)amide or combined peptides but accompanying changes of plasma glucose were small.

Conclusions/interpretation: These data show that (Pro(3))GIP is a specific GIP receptor antagonist. Furthermore, feeding studies in one commonly used animal model of obesity and diabetes, (ob/ob) mice, suggest that GIP is the major physiological component of the enteroinsular axis, contributing approximately 80% to incretin-induced insulin release.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cells, Cultured
  • Cricetinae
  • Cricetulus
  • Cyclic AMP / biosynthesis*
  • Diabetes Mellitus / metabolism*
  • Gastric Inhibitory Polypeptide / metabolism
  • Gastric Inhibitory Polypeptide / pharmacology*
  • Glucagon / pharmacology*
  • Glucagon-Like Peptide 1
  • Glucagon-Like Peptides
  • Humans
  • Hyperinsulinism / blood
  • Insulin / metabolism*
  • Insulin Secretion
  • Mice
  • Obesity*
  • Peptide Fragments / metabolism
  • Peptide Fragments / pharmacology*
  • Postprandial Period
  • Protein Precursors / pharmacology*
  • Spectrometry, Mass, Electrospray Ionization

Substances

  • Insulin
  • Peptide Fragments
  • Protein Precursors
  • glucose-dependent insulinotropic polypeptide, Pro(3)-
  • glucagon-like peptide 1 (7-36)amide
  • exendin (9-39)
  • Gastric Inhibitory Polypeptide
  • Glucagon-Like Peptides
  • Glucagon-Like Peptide 1
  • Glucagon
  • Cyclic AMP