The relaxant effects of adenosine-5′-α,β-methylenediphosphonate on the longitudinal smooth muscle of the rabbit ileum

Abstract

The response pattern of the isolated longitudinal muscle of the rabbit ileum to adenosine-5′-α,β-methylenediphosphonate (APCP) was found to differ from that caused by adenosine or ATP in that the rapid initial phase of relaxation is absent and that at doses above 10 μM a secondary increase of contractile activity occurs in the continued presence of the nucleotide. This secondary phase was attenuated after indomethacin pretreatment and reestablishment of tone with acetylcholine. Theophylline did not modify APCP-induced relaxations while effectively antagonizing those caused by adenosine. It appears that APCP acts via a receptor site or pathway distinct from that of adenosine or ATP.