Characterization of the adenosine receptor responsible for the inhibition of histamine and SRS‐A release from human lung fragments

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Abstract
1 The inhibitory effects of a range of natural and synthetic derivatives of adenosine on the antigen-induced release of histamine and slow reacting substance of anaphylaxis (SRS-A) from human lung has been studied. 2 The nucleotides ATP, ADP and AMP appear to act by being converted to adenosine. 3 The rank order of inhibitory potency of the synthetic analogues indicates that these compounds act at an extracellular A2/Ra purinoceptor. 4 The xanthines, 1, 3-diethyl-8-phenylxanthine, 8-phenyltheophylline and theophylline antagonized the inhibitory action of N-ethyl-carboxamideadenosine competitively. Theobromine was inactive. This supports the view that the inhibitory receptor is of the A/R type. 5 Hexobendine and dipyridamole, reported to antagonize the uptake of adenosine, failed to modify the response of human lung fragments to adenosine. 6 The P site agonist 2′, 5′ dideoxyadenosine inhibited the release of histamine and SRS-A. This effect was not prevented by the inhibitors of uptake, hexobendine and dipyridamole, nor was it antagonized by 8-phenyltheophylline.