Abstract
Adenosine has been demonstrated to inhibit gastric acid secretion. In the rat stomach, this inhibitory effect may be mediated indirectly by increasing the release of somatostatin-like immunoreactivity (SLI). Results show that adenosine analogs augmented SLI release in the isolated vascularly perfused rat stomach. The rank order of potency of the analogs in stimulating SLI release was 2-p-(2-carboxyethyl)phenethylamino-5′-N-ethylcarboxamidoadenosine (CGS 21680) ≈ 5′-N-ethylcarboxamidoadenosine > 2-chloroadenosine > R-(-)-N6-(2-phenylisopropyl)adenosine >1-deoxy-1-[6-[[(3-iodophenyl)methyl]amino]-9H-purin-9-yl]-N-methyl-β-d-ribofuranuronamide > N6-cyclopentyladenosine ≈ N6-cyclohexyladenosine > S-(+)-N6-(2-phenylisopropyl) adenosine, suggesting the involvement of the A2A receptor. In agreement, 4-(2-[7-amino-2-(2-furyl)[1,2,4]triazolo[2,3-a] [1,3,5]triazin-5-ylamino]ethyl)phenol (ZM 241385), an A2A receptor antagonist, was shown to abolish the adenosine- and CGS 21680-stimulated SLI release. Immunohistochemical studies reveal the presence of A2A receptor immunoreactivity on the gastric plexi and mucosal D-cells, but not on parietal cells and G-cells, suggesting that adenosine may act directly on D-cells or indirectly on the gastric plexi to augment SLI release. The present study also demonstrates that the structure of the mucosal A2A receptor is identical to that in the rat brain, and that alternative splicing of this gene does not occur. A real-time reverse transcription-polymerase chain reaction assay has also been established to quantify the levels of A2A receptor mRNA. Results show that gastric tissues contained significantly lower levels of A2A receptor mRNA compared with the striatum. The lowest level was detected in the mucosa. In conclusion, adenosine may act on A2A receptors to augment SLI release and consequently control gastric acid secretion.
Footnotes
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This work was supported by the Canadian Apoptosis Research Foundation Society, Canada Foundation for Innovation, Wah Sheung Fund, and the former British Columbia Health Research Foundation. L.Y. was supported by the Cordula and Gunter Paetzold Fellowship and the University of British Columbia Graduate Fellowship. A portion of this work was included in L.Y.'s Ph.D. dissertation entitled, Adenosine A1 and A2A Receptors in the Rat Stomach: Biological Actions, Cellular Localization, Structure, and Gene Expression. Citation of meeting abstracts where part of this work was previously presented: Kwok YN and Hui J (1992) Effect of selective adenosine A1 and A2 analogs on the release of gastric somatostatin-like immunoreactivity. Regul Pept40:189; Kwok YN (1994) Purinergic control of release of somatostatin in the rat stomach. Pathophysiol Suppl1:218; Yip L and Kwok Y (2002) Gastric A1 and A2A receptors: cellular localization, gene sequence and gene expression levels. Drug Dev Res56:551; and Yip L, Leung CH, and Kwok YN (2003) Cellular localization of adenosine A1 and A2A receptors in the rat stomach. FASEB J17:A40.
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DOI: 10.1124/jpet.103.061986.
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ABBREVIATIONS: ADA, adenosine deaminase; SLI, somatostatin-like immunoreactivity; IR, immunoreactivity; RT-PCR, reverse transcription-polymerase chain reaction; BSA, bovine serum albumin; RIA, radioimmunoassay; 2-CA, 2-chloroadenosine; CPA, N6-cyclopentyladenosine; CGS 21680, 2-p-(2-carboxyethyl)phenethylamino-5′N-ethylcarboxamidoadenosine; CHA, 5′-N6-cyclohexyladenosine; NECA, N-ethylcarboxamidoadenosine; R-PIA, R(-)-N6-(2-phenylisopropyl)adenosine; S-PIA, (S)-N6-(2-phenylisopropyl)adenosine; IB-MECA, 1-deoxy-1-[6-[[(3-iodophenyl)methyl]amino]-9H-purin-9-yl]-N-methyl-β-d-ribofuranuronamide; DPCPX, 8-cyclopentyl-1,3-dipropylxanthine; ZM 241385, 4-(2-[7-amino-2-(2-furyl)[1,2,4]triazolo[2,3-a][1,3,5]triazin-5-ylamino]ethyl)phenol; ENHA, erythro-9-(2-hydroxy-3-nonyl)adenine hydrochloride; DMSO, dimethyl sulfoxide; PBS, phosphate-buffered saline; A2AR-IR, A2A receptor-immunoreactivity; PGP 9.5, protein gene product 9.5; VWF, von Willebrand's factor; bp, base pair(s); UNG, uracil-N-glycosylase; CT, threshold cycle.
- Received October 22, 2003.
- Accepted January 16, 2004.
- The American Society for Pharmacology and Experimental Therapeutics
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