SYNTHESIS AND SECRETION OF GLUCAGON-LIKE PEPTIDE-1 BY FETAL-RAT INTESTINAL-CELLS IN CULTURE

Secretion of the intestinal proglucagon-derived peptides (PGDPs) including the incretin glucagon-like peptide-1 (GLP-1) is regulated, at least in part, by the duodenal hormone glucose-dependent insulinotropic peptide (GIP) through a protein kinase (PK) A-dependent pathway. It has been demonstrated that the activation of PKA increases the synthesis of some intestinal PGDPs, particularly the glucagon-like immunoreactive (GLI) peptides glicentin and oxyntomodulin. However; the effects of CIP on CLI and GLP-1 synthesis are not known. Fetal rat intestinal cells in culture were therefore treated for up to 24 h with 5 mM dbcAMP or 10(-6) M GIP and the changes in glicentin, oxyntomodulin, GLP-1(x-37) and GLP-1(x-36NH2) secretion and synthesis were examined by RIA and HPLC. Both dbcAMP and GIP increased the acute (2 h; to 224 +/- 21 and 256 +/- 20% of controls, respectively, P<0.001) and chronic (24 h; to 230 +/- 22 and 130 +/- 6% of controls, respectively, P<0.001) secretion of intestinal PGDPs. In contrast, the total culture content of PGDPs was increased only after 24 h of incubation (to 156 +/- 15 and 125 +/- 7% of controls for dbcAMP and GIP, respectively, P<0.01). HPLC analysis confirmed that the intestinal cultures produced the GLI peptides glicentin and oxyntomodulin, as well as the biologically active forms of GLP-1, GLP-1(7-37) and GLP-1(7-36NH2). The relative proportion of these peptides was not altered by treatment with dbcAMP or GIP. Thus, in addition to its effects on GLP-1 release from the rat intestine, CIP appears to be an important regulator of the synthesis of this insulinotropic peptide.