title: Insulinotropic glucagon-like peptide I receptor expression in glucagon-producing alpha-cells of the rat endocrine pancreas.
abstract: Glucagon-like peptide I (GLP-I), an intestine-derived incretin hormone, is a potent stimulator of insulin and somatostatin secretion. In some studies, GLP-I is an inhibitor of glucagon secretion. It remains uncertain, however, whether the effect of GLP-I on the inhibition of glucagon secretion is direct, owing to interactions with GLP-I receptors on alpha-cells, or indirect, via paracrine suppression by insulin or somatostatin. The localization of the GLP-I receptor on insulin and somatostatin-producing cells in the islets is well established. Whether the GLP-I receptor also resides on the glucagon-producing alpha-cells remains controversial and is reported to be absent on rat alpha-cells. To investigate the distribution of the GLP-I receptor on islet cells, we examined the expression of GLP-I receptor mRNA in phenotypically distinct islet cell lines and islets, and the presence of immunoreactive GLP-I receptor in dispersed rat islet cells using a specific antiserum. GLP-I receptor mRNA was readily detected by reverse transcription-polymerase chain reaction (RT-PCR) in both rat islets and in established islet cell lines representing distinct alpha-, beta-, and delta-cell phenotypes. In addition, GLP-I receptor expression was detected in single rat alpha-cells by single-cell RT-PCR. In dispersed rat islet cells analyzed by double immunofluorescent staining, 90% of the insulin, 76% of the somatostatin, and 20% of the glucagon positive cells colocalized with the GLP-I receptor immunoreactivity. Thus, a substantial population of glucagon immunoreactive a-cells express the GLP-I receptor. These findings imply that GLP-I may have a direct receptor-mediated action in the regulation of the physiological functions on a substantial subpopulation of alpha-cells. We suggest that a possible role for GLP-I receptors on alpha-cells may be to provide positive autocrine feedback control on glucagon secretion during fasting and/or to dampen the potent paracrine suppression of glucagon secretion by insulin during feeding.
authors.affiliation: Laboratory of Molecular Endocrinology, Massachusetts General Hospital, Howard Hughes Medical Institute, Harvard Medical School, Boston 02114, USA.
authors.forename: R S
authors.initials: RS
authors.lastname: Heller
authors.forename: T J
authors.initials: TJ
authors.lastname: Kieffer
authors.forename: J F
authors.initials: JF
authors.lastname: Habener
mesh_terms: D000818:Animals; D002460:Cell Line; D005260:Female; D005934:Glucagon / Q000378:metabolism*; D000067757:Glucagon-Like Peptide-1 Receptor; D007106:Immune Sera / Q000494:pharmacology; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000737:chemistry* / Q000378:metabolism; D008297:Male; D016133:Polymerase Chain Reaction; D012194:RNA-Directed DNA Polymerase; D051381:Rats; D017207:Rats, Sprague-Dawley; D018027:Receptors, Glucagon / Q000096:biosynthesis* / Q000276:immunology
chemical_list: C000593835:Glp1r protein, rat; D000067757:Glucagon-Like Peptide-1 Receptor; D007106:Immune Sera; D007328:Insulin; D018027:Receptors, Glucagon; D005934:Glucagon; D012194:RNA-Directed DNA Polymerase