Title : Involvement of Adenosine Signaling in Controlling the Release of Ghrelin from the Mouse Stomach

Ghrelin, a potent orexigenic hormone released from the stomach, is important in regulating energy metabolism. Abnormal ghrelin levels are associated with eating disorders and metabolic diseases. However, factors involved in the regulation of ghrelin release remain unclear. Here we examined the involvement of adenosine signaling in the control of ghrelin release from the perfused mouse stomach. Adenosine stimulated ghrelin release concentration-dependently and the A2A receptor-selective antagonists, ZM 241385 (4-(2-[7-amino-2-(2-furyl)[1,2,4]triazolo[2,3-a][1,3,5]triazin-5ylamino]ethyl)phenol) and SCH 58261 (2-(2-Furanyl)-7-(2-phenylethyl)-7H-pyrazolo[4,3-e][1,2, 4]triazolo[1,5-c]pyrimidin-5-amine), abolished the increased release. The A2A receptor-selective agonist, CGS 21680 (2-p-(2-carboxyethyl)phenethylamino-5-N-ethylcarboxamidoadenosine hydrochloride), augmented ghrelin release concentration-dependently, whereas the A1 receptor-selective agonist, CCPA (2-chloro-N-cyclopentyladenosine), inhibited ghrelin release. In A2A receptor knockout mice, adenosine inhibited ghrelin release and the A1 receptor-selective antagonist, DPCPX (8-cyclopentyl-1,3dipropylxanthine), blocked this inhibition. The adenosine deaminase inhibitor, EHNA (erythro-9-(2hydroxy-3-nonyl)adenine hydrochloride), increased ghrelin release in wild type and A1 receptor knockout mice but not in A2A receptor knockout mice. Co-localization of ghrelin immunoreactivity with A1 and A2A receptor immunoreactivities in the gastric nerve fibers were observed. Co-localization was also detected for ghrelin and A1 receptor immunoreactivities in the gastric mucosa. Blockade of neural activities with tetrodotoxin abolished the stimulatory effect of adenosine on ghrelin release. In conclusion, adenosine exerts predominantly a tonic A2A receptor-mediated stimulatory action on gastric ghrelin release, while an A1 receptor-mediated inhibitory action is also apparent when the tonic excitatory effect was removed. This article has not been copyedited and formatted. The final version may differ from this version. JPET Fast Forward. Published on September 27, 2010 as DOI: 10.1124/jpet.110.171280 at A PE T Jornals on A ril 3, 2017 jpet.asjournals.org D ow nladed from