POTENTIATION BY DIPYRIDAMOLE OF INHIBITION OF GUINEA-PIG ILEUM TWITCH RESPONSE CAUSED BY ADENINE-DERIVATIVES

Abstract

The inhibitory actions of adenosine and adenine nucleotides, such as ATP, AMP and cyclic AMP, on contractions of guinea pig ileum induced by transmural stimulation were potentiated by dipyridamole, whereas those of inosine, morphine and tetrodotoxin were not affected. 3H activity, accumulated during incubation of the ileal segments with [3H]adenosine, was reduced by dipyridamole. The adenosine added was degraded to inosine and then hypoxanthine during incubation with the ileal segments, thereby restoring the twitch response of the ileal segments. In the presence of dipyridamole, the degradation of adenosine and the recovery of the twitch response was retarded. Thus, dipyridamole may potentiate the inhibitory actions of adenosine and adenine nucleotides on the twitch response of the ileum by inhibiting both the accumulation and degradation of adenosine.