Abstract
The changes in the electrical activity of the antrum muscle fibers of the guinea pig stomach caused by ATP and its related compounds were compared with those caused by catecholamines. The antrum preparation exhibited spontaneous electrical activity and this was suppressed or inhibited by treatment with catecholamines (adrenaline, noradrenaline and isoprenaline). The inhibitory actions of catecholamines were observed in the presence of tetrodotoxin or alpha-blockers (phentolamine or phenoxybenzamine) while the effects were antagonized by beta-blockers (propranolol or DCI). At higher concentrations than that of catecholamines, ATP or related nucleotides also produced the inhibitory effect on the spike activity and the generation of slow waves. The inhibitory actions of ATP and related substances were still observed in the presence of alpha- or beta-adrenergic blockers. Furthermore, the inhibition was present after treatment with tetrodotoxin. From these results, it is concluded that the inhibitory action of ATP and related compounds is due to a direct action on the antrum muscle and is not mediated via alpha- or beta-adrenoceptors.
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