Evidence for A2 adenosine receptor-mediated effects on adenylate cyclase activity in rat ovarian membranes

Effects of adenosine analogues on adenylate cyclase activity in preovulatory rat ovarian membranes were studied. Adenosine analogues stimulated adenylate cyclase activity in the following rank order of potency: NECA (5'-(N-ethyl)carboxamidoadenosine) greater than 2-chloroadenosine greater than N6-(R-phenylisopropyl)-adenosine greater than N6-(S-phenylisopropyl)adenosine. The apparent EC50 for NECA was 0.28 microM. The adenosine receptor antagonist 8-phenyltheophylline (10 microM) displaced the dose-response curve for NECA to the right, increasing the EC50 for NECA about one order of magnitude. NECA also additively increased maximally FSH-stimulated adenylate cyclase activity. These results suggest that adenosine stimulates adenylate cyclase in rat ovarian membranes via adenosine receptors of the A2 type.