Identification of specific binding sites for glucagon-like peptide-1 on the posterior lobe of the rat pituitary

Neuroendocrinology. 1995 Aug;62(2):130-4. doi: 10.1159/000126997.

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)

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Autoradiography
  • Binding Sites
  • Binding, Competitive
  • Exenatide
  • Glucagon / analysis*
  • Glucagon / metabolism
  • Glucagon-Like Peptide 1
  • Iodine Radioisotopes
  • Lizards
  • Male
  • Peptide Fragments / analysis*
  • Peptides / metabolism
  • Pituitary Gland, Posterior / chemistry*
  • Protein Precursors / analysis*
  • Rats
  • Rats, Wistar
  • Vasoactive Intestinal Peptide / metabolism
  • Venoms

Substances

  • Iodine Radioisotopes
  • Peptide Fragments
  • Peptides
  • Protein Precursors
  • Venoms
  • Vasoactive Intestinal Peptide
  • Glucagon-Like Peptide 1
  • Glucagon
  • Exenatide