Disordered
glucagon secretion contributes to the symptoms of diabetes, and reduced
glucagon action is known to improve
glucose homeostasis. In mice, genetic deletion of the
glucagon receptor (Gcgr) results in increased levels of the insulinotropic
hormone glucagon-like peptide 1 (GLP-1), which may contribute to the alterations in
glucose homeostasis observed in Gcgr-/- mice. Here, we assessed the contribution of
GLP-1 receptor (GLP-1R) signaling to the phenotype of Gcgr-/- mice by generating Gcgr-/-Glp1r-/- mice. Although
insulin sensitivity was similar in all genotypes, fasting
glucose was increased in Gcgr-/-Glp1r-/- mice. Elimination of the Glp1r normalized gastric emptying and impaired intraperitoneal
glucose tolerance in Gcgr-/- mice. Unexpectedly, deletion of Glp1r in Gcgr-/- mice did not alter the improved oral
glucose tolerance and increased insulin secretion characteristic of that genotype. Although Gcgr-/-Glp1r-/- islets exhibited increased sensitivity to the
incretin glucose-dependent insulinotropic
polypeptide (GIP), mice lacking both Glp1r and the
GIP receptor (Gipr) maintained preservation of the enteroinsular axis following reduction of Gcgr signaling. Moreover, Gcgr-/-Glp1r-/- islets expressed increased levels of the
cholecystokinin A receptor (Cckar) and
G protein-coupled receptor 119 (Gpr119)
mRNA transcripts, and Gcgr-/-Glp1r-/- mice exhibited increased sensitivity to exogenous CCK and the GPR119 agonist
AR231453. Our data reveal extensive functional plasticity in the enteroinsular axis via induction of compensatory mechanisms that control nutrient-dependent regulation of insulin secretion.