Endogenous adenosine inhibits evoked substance P release from perifused networks of myenteric ganglia.

Isolated myenteric ganglion networks were prepared from guinea pig ileum and were used in a perifusion protocol to examine the effects of interstitial adenosine on evoked release of substance P-like immunoreactivity (SPLI). The release of SPLI evoked by elevated extracellular K+ concentration was increased in the presence of tetrodotoxin (TTX), indicating tonic inhibition of SPLI release and revealing net inhibitory interganglionic transmission. Perifusion in the presence of the adenosine A1 receptor-selective antagonist 1,3-dipropyl-8-cyclopentylxanthine enhanced evoked SPLI release, which was further enhanced in the additional presence of TTX, indicating that adenosine contributes some, but not all, of the overall inhibitory tone within the networks. In addition to neural release of adenosine per se, an additional source was investigated. Perifusion in the presence of alpha, beta-methylene-ADP plus guanosine 5'-monophosphate, which inhibits ecto-adenosinetriphosphatase (ATPase) activity, enhanced SPLI release, indicating that hydrolysis of released ATP contributes to the total interstitial nucleoside concentration and thereby to the overall inhibitory tone. It is concluded that endogenous adenosine, some of which arises from ATP metabolism, is an important contributor to the overall inhibitory tone present in myenteric ganglion networks.