Adenosine receptors in papilla of human kidneys

Adenylate cyclase activity in homogenates of human papillae was stimulated by adenosine agonist compounds. The rank order of agonist potencies for stimulation was 5'-N-ethylcarboxamidoadenosine greater than L-N6-phenylisopropyladenosine greater than 2-chloroadenosine greater than N6-cyclohexyladenosine greater than D-N6-phenylisopropyladenosine. This order of agonist potencies is similar to that observed at adenylate cyclase-coupled A2-adenosine receptors in many different tissues. The methylxanthines 8-phenyltheophylline and 1,3-diethyl-8-phenylxanthine acted as competitive antagonists, with 1,3-diethyl-8-phenylxanthine being approximately 10 times more potent than 8-phenyltheophylline. This study demonstrates the presence of A2-adenosine receptors in the papilla of human kidney. These receptors are similar to adenosine receptors previously observed in the renal papillae of the rat in terms of both agonist and antagonist potencies.