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

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.