Coexpression of Glucagon-Like Peptide-1 (GLP-1) Receptor, Vasopressin, and Oxytocin mRNAs in Neurons of the Rat Hypothalamic Supraoptic and Paraventricular Nuclei

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Abstract

This study was designed to gain better insight into the relationship between glucagon-like peptide-1 (GLP-1) (7-36) amide and vasopressin (AVP) and oxytocin (OX). In situ hybridization histochemistry revealed colocalization of the mRNAs for GLP-1 receptor, AVP, and OX in neurons of the hypothalamic supraoptic and paraventricular nuclei. To determine whether GLP-1(7-36)amide alters AVP and/or OX release, both in vivo and in vitro experimental study designs were used. In vivo, intravenous administration of 1 microg of GLP-1(7-36)amide into the jugular vein significantly decreased plasma AVP and OX concentrations. In vitro incubation of the neurohypophysis with either 0.1 or 1 microg of GLP-1(7-36)amide did not modify the release of AVP. However, addition of 1 microg of GLP-1(7-36)amide to the incubation medium increased slightly the secretion of OX. The coexpression of GLP-1 receptor and AVP mRNAs in hypothalamic supraoptic and paraventricular nuclei gives further support to the already reported central effects of GLP-1 (7-36)amide on AVP. Our findings also suggest a dual secretory response of AVP and OX to the effect of GLP-1 (7-36)amide, which most likely is related to the amount and/or the route of peptide administration.

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Expression cloning of the pancreatic beta cell receptor for the gluco-incretin hormone glucagon-like peptide 1.

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Glucagon-like peptide 1 (GLP-1) is a hormone derived from the preproglucagon molecule and is secreted by intestinal L cells. It is the most potent stimulator of glucose-induced insulin secretion and also suppresses in vivo acid secretion by gastric glands. A cDNA for the GLP-1 receptor was isolated by transient expression of a rat pancreatic islet cDNA library into COS cells; this was followed by binding of radiolabeled GLP-1 and screening by photographic emulsion autoradiography. The receptor transfected into COS cells binds GLP-1 with high affinity and is coupled to activation of adenylate cyclase. The receptor binds specifically GLP-1 and does not bind peptides of related structure and similar function, such as glucagon, gastric inhibitory peptide, vasoactive intestinal peptide, or secretin. The receptor is 463 amino acids long and contains seven transmembrane domains. Sequence homology is found only with the receptors for secretin, calcitonin, and parathyroid hormone, which form a newly characterized family of G-coupled receptors.

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Tissue-specific expression of the human receptor for glucagon-like peptide-I: brain, heart and pancreatic forms have the same deduced amino acid sequences.

Y Wei, S Mojsov (1995)

Glucagon-like peptide-I(GLP-I), encoded by the glucagon gene and released from the gut in response to nutrients, is a potent stimulator of glucose-induced insulin secretion. In human subjects GLP-I exerts its physiological effect as an incretin. The incretin effect of GLP-I is preserved in patients with Type II diabetes mellitus (NIDDM), suggesting that GLP-I receptor agonist can be used therapeutically in this group of patients. In these studies we addressed the question of whether GLP-I has broader actions in human physiology. To investigate this issue we examined the tissue distribution of GLP-I receptor using RNAse protection assay in order to avoid the cross-reactivities with structurally related receptors and to increase the sensitivity of detection. The riboprobe was synthesized from the human pancreatic GLP-I receptor cDNA and used in hybridization experiments with total RNA isolated from different human tissues. In addition to the pancreas, we found expression of GLP-I receptor mRNA in lung, brain, kidney, stomach and heart. Peripheral tissues which are the major sites of glucose turnover, such as liver, skeletal muscle and adipose did not express the pancreatic form of the GLP-I receptor. We also cloned and sequenced GLP-I receptor cDNA from human brain and heart. The deduced amino acid sequences are the same as the sequence found in the pancreas. These results indicate that GLP-I might have effects beyond the pancreas, including the cardiovascular and central nervous systems where a receptor with the same ligand binding specificity is found.

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Induction of intestinal epithelial proliferation by glucagon-like peptide 2.

S Asa, P Erlich, Daniel Drucker … (1996)

Injury, inflammation, or resection of the small intestine results in severe compromise of intestinal function. Nevertheless, therapeutic strategies for enhancing growth and repair of the intestinal mucosal epithelium are currently not available. We demonstrate that nude mice bearing subcutaneous proglucagon-producing tumors exhibit marked proliferation of the small intestinal epithelium. The factor responsible for inducing intestinal proliferation was identified as glucagon-like peptide 2 (GLP-2), a 33-aa peptide with no previously ascribed biological function. GLP-2 stimulated crypt cell proliferation and consistently induced a marked increase in bowel weight and villus growth of the jejunum and ileum that was evident within 4 days after initiation of GLP-2 administration. These observations define a novel biological role for GLP-2 as an intestinal-derived peptide stimulator of small bowel epithelial proliferation.