Increase of [3H]clonidine binding sites induced by adenosine receptor agonists in rat vas deferens in vitro.

In vitro binding experiments were done to study the effects of adenosine receptor agonists on induction of [3H]clonidine binding sites in rat vasa deferentia by reserpine. In the presence of 1 microM adenosine and 2-chloroadenosine, respectively, the specific binding of [3H]clonidine to vas deferens homogenates of reserpine-treated rats increased 38 and 42% over the control value. The increase in binding sites induced by adenosine was inhibited by the adenosine receptor antagonist theophylline. No effect of 1 microM 2-chloroadenosine on the beta-adrenoceptor or alpha 1-adrenoceptor was detected. The results imply a direct interaction between alpha 2-adrenoceptor and adenosine receptor and suggest that stimulated adenosine receptors unmasked [3H]clonidine binding sites in membranes of rat vas deferens.