Evidence for adenosine A2b receptors in the rat pineal gland.

We describe the effects of 5'-N-ethylcarboxamidoadenosine (NECA), a mixed A2a/A2b adenosine receptor agonist and 2-[p-(carboxyethyl)-phenylethylamino]-5'-N-ethylcarboxamidoaden osin e (CGS 21680), a selective A2a agonist, on cyclic AMP and N-acetylserotonin synthesis in rat pineal gland. NECA, 1 and 10 microM, increased cyclic AMP by 5- and 25-fold and N-acetylserotonin by 40- and 60-fold respectively, whereas CGS 21680 at the same concentrations was ineffective. These results argue for the presence of adenosine A2b receptors in rat pinealocytes.