title: Enhanced glucose-dependent insulinotropic polypeptide secretion and insulinotropic action in glucagon-like peptide 1 receptor -/- mice.
abstract: Incretins are gastrointestinal hormones that act on the pancreas to potentiate glucose-stimulated insulin secretion. Despite the physiological importance of the enteroinsular axis, disruption of glucagon-like peptide (GLP)-1 action is associated with only modest glucose intolerance in GLP-1 receptor -/- (GLP-1R -/-) mice. We show here that GLP-1R -/- mice exhibit compensatory changes in the enteroinsular axis via increased glucose-dependent insulinotropic polypeptide (GIP) secretion and enhanced GIP action. Serum GIP levels in GLP-1R -/- mice were significantly elevated versus those in +/+ control mice after an oral glucose tolerance test (369 +/- 40 vs. 236 +/- 28 pmol/l; P < or = 0.02). Furthermore, GIP perfusion of mice pancreas and isolated islets in the presence of elevated glucose concentrations elicited a significantly greater insulin response in GLP-1R -/- than in +/+ mice (P < or = 0.02-0.05). In contrast, no significant perturbation in the insulin response to perfused glucagon was detected under conditions of low (4.4 mmol/l) or high (16.6 mmol/l) glucose in GLP-1R -/- mice. Total pancreatic insulin but not glucagon content was significantly reduced in GLP-1R -/- compared with in +/+ mice (77 +/- 9 vs. 121 +/- 10 pmol/mg protein; P < or = 0.005). These observations suggest that upregulation of the GIP component of the enteroinsular axis, at the levels of GIP secretion and action, modifies the phenotype resulting from interruption of the insulinotropic activity of GLP-1 in vivo.
authors.affiliation: Department of Physiology, University of British Columbia, Vancouver, Canada. pederson@unixg.ubc.ca
authors.forename: R A
authors.initials: RA
authors.lastname: Pederson
authors.forename: M
authors.initials: M
authors.lastname: Satkunarajah
authors.forename: C H
authors.initials: CH
authors.lastname: McIntosh
authors.forename: L A
authors.initials: LA
authors.lastname: Scrocchi
authors.forename: D
authors.initials: D
authors.lastname: Flamez
authors.forename: F
authors.initials: F
authors.lastname: Schuit
authors.forename: D J
authors.initials: DJ
authors.lastname: Drucker
authors.forename: M B
authors.initials: MB
authors.lastname: Wheeler
mesh_terms: D000818:Animals; D001786:Blood Glucose / Q000378:metabolism; D005749:Gastric Inhibitory Polypeptide / Q000097:blood / Q000378:metabolism* / Q000494:pharmacology; D005934:Glucagon / Q000378:metabolism / Q000494:pharmacology; D000067757:Glucagon-Like Peptide-1 Receptor; D005951:Glucose Tolerance Test; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism; D051379:Mice; D008817:Mice, Mutant Strains; D010179:Pancreas / Q000187:drug effects / Q000378:metabolism; D010187:Pancreatic Hormones / Q000378:metabolism; D011384:Proinsulin / Q000096:biosynthesis / Q000235:genetics; D012333:RNA, Messenger / Q000378:metabolism; D018027:Receptors, Glucagon / Q000235:genetics* / Q000502:physiology*
chemical_list: D001786:Blood Glucose; C000593834:Glp1r protein, mouse; D000067757:Glucagon-Like Peptide-1 Receptor; D007328:Insulin; D010187:Pancreatic Hormones; D012333:RNA, Messenger; D018027:Receptors, Glucagon; D005749:Gastric Inhibitory Polypeptide; D005934:Glucagon; D011384:Proinsulin