Effects of adenosine on contractile response of circular muscle in electrically stimulated guinea-pig ileum.

The action of adenosine on the electrically induced mechanical response of circular muscle in isolated guinea-pig ileum has been investigated. Electrical stimulation (0.1 Hz) elicited the twitch response, which was completely abolished by tetrodotoxin (0.2 microM), morphine (1 microM) and atropine (0.1 microM). Adenosine (0.1-100 microM) markedly depressed the twitch response in a concentration-dependent manner, and the concentration-depression curve for adenosine was significantly shifted to the right in the presence of theophylline (30 microM). On the other hand, the contractile responses induced by acetylcholine (1-300 microM) were not effected by adenosine at all. The present investigation suggests that the twitch response is mediated through acetylcholine released from the intramural cholinergic nerves supplying the circular muscle of guinea-pig ileum, and adenosine has an inhibitory effect on the cholinergic transmission, probably via P1-purinoceptors.