title: Identification of specific binding sites for glucagon-like peptide-1 on the posterior lobe of the rat pituitary.
abstract: Glucagon-like peptide-1 (GLP-1) immunoreactivity has been found in autonomic and neuroendocrine brain regions, whereas only limited data are available regarding the characterization and localization of brain GLP-1 receptors. In the present study, using quantitative in vitro autoradiography, a high density of specific binding sites for GLP-1 was characterized on sections of the posterior pituitary lobe of the rat. Low specific binding of radiolabeled GLP-1 was found in the anterior lobe and no specific binding in the intermediate lobe. To examine the specificity of GLP-1 binding sites, sections of the posterior lobe were incubated with radiolabeled GLP-1 in the presence of various peptides. Radiolabeled [Tyr39]exendin-4, a specific GLP-1 agonist, bound to these receptor sites with the same affinity as GLP-1, while glucagon and vasoactive intestinal peptide (VIP) were unable to displace 125I-GLP-1. Both unlabeled exendin-4 and GLP-1 inhibited this binding with equally high affinity. Using 125I-[Tyr39]exendin-4 as radiolabel, the concentration of biding sites was found to be 7.8 +/- 0.4 fmol/mg tissue. Further analysis of the binding data from experiments with tissue slices revealed the presence of high and low affinity binding sites. In experiments with unlabeled [Tyr39]exendin-4, the KdS were 6.2 +/- 1.4 x 10(-12) and 9.3 +/- 1.5 x 10(-10) M, respectively, and in experiments with unlabeled GLP-1, 3.4 +/- 1.8 x 10(-12) and 5.9 +/- 1.5 x 10(-10) M, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Laboratory of Clinical Pharmacology, Rigshospitalet, Denmark.
authors.forename: R
authors.initials: R
authors.lastname: Göke
authors.forename: P J
authors.initials: PJ
authors.lastname: Larsen
authors.forename: J D
authors.initials: JD
authors.lastname: Mikkelsen
authors.forename: S P
authors.initials: SP
authors.lastname: Sheikh
mesh_terms: D000818:Animals; D001345:Autoradiography; D001665:Binding Sites; D001667:Binding, Competitive; D000077270:Exenatide; D005934:Glucagon / Q000032:analysis* / Q000378:metabolism; D052216:Glucagon-Like Peptide 1; D007457:Iodine Radioisotopes; D008116:Lizards; D008297:Male; D010446:Peptide Fragments / Q000032:analysis*; D010455:Peptides / Q000378:metabolism; D010904:Pituitary Gland, Posterior / Q000737:chemistry*; D011498:Protein Precursors / Q000032:analysis*; D051381:Rats; D017208:Rats, Wistar; D014660:Vasoactive Intestinal Peptide / Q000378:metabolism; D014688:Venoms
chemical_list: D007457:Iodine Radioisotopes; D010446:Peptide Fragments; D010455:Peptides; D011498:Protein Precursors; D014688:Venoms; D014660:Vasoactive Intestinal Peptide; D052216:Glucagon-Like Peptide 1; D005934:Glucagon; D000077270:Exenatide