Demonstration of RA - adenosine receptors in rat renal papillae.

Adenylate cyclase in homogenates of rat renal papillae was stimulated by adenosine agonist compounds. Adenosine agonists neither stimulated nor inhibited cyclase activity in cortex or medulla. The rank order of agonist potencies was 5'N- ethylcarboxamide adenosine much greater than 2-chloroadenosine greater than L-N6-phenylisopropyladenosine = cyclohexyladenosine greater than D-N6-phenylisopropyladenosine. Stimulation of adenylate cyclase by 5'N- ethylcarboxamide adenosine was competitively antagonised by the methylxanthines, 1,3-diethyl-8- phenylxanthine and 8-phenyltheophylline; 1,3-diethyl-8- phenylxanthine being approximately 10 times more potent than 8-phenyltheophylline. These results demonstrate adenosine receptors of the RA-type localized to the papilla of the rat kidney.