title: Adenosine: A partial agonist of the growth hormone secretagogue receptor.
abstract: The growth hormone secretagogue receptor (GHS-R) is involved in the regulation of pulsatile GH release. However, until recently, natural endogenous ligands for the receptor were unknown. We fractionated porcine hypothalamic extracts and assayed fractions for activity on HEK293 cells expressing GHS-R and aequorin. A partial agonist was isolated and identified using microspray tandem mass spectrometry as adenosine. GHS-R activation by adenosine and synthetic adenosine agonists is inhibited by the GHS-R selective antagonists L-765,867, D-Lys(3)-GHRP-6, and by theophylline and XAC. Cross desensitization of the GHS-R occurs with both MK-0677 and adenosine. Ligand binding and site directed mutagenesis studies show that adenosine binds to a binding site that is distinct from the previously characterized MK-0677 and GHRP-6 binding pocket. We propose, that adenosine is a physiologically important endogenous GHS-R ligand and speculate that GHS-R ligands modulate dopamine release from hypothalamic neurons.
authors.affiliation: Huffington Center on Aging, Baylor College of Medicine, Houston, Texas, USA. rsmith@bcm.tmc.edu
authors.forename: R G
authors.initials: RG
authors.lastname: Smith
authors.forename: P R
authors.initials: PR
authors.lastname: Griffin
authors.forename: Y
authors.initials: Y
authors.lastname: Xu
authors.forename: A G
authors.initials: AG
authors.lastname: Smith
authors.forename: K
authors.initials: K
authors.lastname: Liu
authors.forename: J
authors.initials: J
authors.lastname: Calacay
authors.forename: S D
authors.initials: SD
authors.lastname: Feighner
authors.forename: C
authors.initials: C
authors.lastname: Pong
authors.forename: D
authors.initials: D
authors.lastname: Leong
authors.forename: A
authors.initials: A
authors.lastname: Pomés
authors.forename: K
authors.initials: K
authors.lastname: Cheng
authors.forename: L H
authors.initials: LH
authors.lastname: Van der Ploeg
authors.forename: A D
authors.initials: AD
authors.lastname: Howard
authors.forename: J
authors.initials: J
authors.lastname: Schaeffer
authors.forename: R J
authors.initials: RJ
authors.lastname: Leonard
mesh_terms: D000241:Adenosine / Q000031:analogs & derivatives* / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000494:pharmacology*; D019830:Adenosine-5'-(N-ethylcarboxamide) / Q000494:pharmacology; D000331:Aequorin / Q000378:metabolism; D000818:Animals; D001665:Binding Sites; D002457:Cell Extracts; D002460:Cell Line; D002851:Chromatography, High Pressure Liquid; D004298:Dopamine / Q000378:metabolism; D006801:Humans; D007031:Hypothalamus / Q000166:cytology / Q000187:drug effects; D007211:Indoles / Q000494:pharmacology; D008024:Ligands; D008163:Luminescent Measurements; D013058:Mass Spectrometry; D008954:Models, Biological; D016297:Mutagenesis, Site-Directed; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000819:agonists* / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism; D043562:Receptors, G-Protein-Coupled; D054440:Receptors, Ghrelin; D013141:Spiro Compounds / Q000494:pharmacology; D013552:Swine; D013806:Theophylline / Q000494:pharmacology
chemical_list: D002457:Cell Extracts; D007211:Indoles; D008024:Ligands; D011956:Receptors, Cell Surface; D043562:Receptors, G-Protein-Coupled; D054440:Receptors, Ghrelin; D013141:Spiro Compounds; C084956:N(6)-(3-iodobenzyl)-5'-N-methylcarboxamidoadenosine; D019830:Adenosine-5'-(N-ethylcarboxamide); D000331:Aequorin; D013806:Theophylline; D000241:Adenosine; C094817:ibutamoren mesylate; D004298:Dopamine