An Analysis of the Mechanical Reponses of the Isolated Ileum to Single Transmural Stimulation and to Drugs

1. A study was made of the mechanical responses of the isolated ileum of the guinea-pig to single transmural stimulation of the intrinsic nerves and to drugs. 2. Excitatory dominant and inhibitory dominant types of responses were observed. Rebound-contraction produced by single transmural stimulation was also demonstrated. 3. Atropine or hyoscine abolished the primary contraction and produced the relaxation type response. The initial relaxation was dependent on the tension level at which the single transmural stimulation was given. 4. TTX but not hexamethonium inhibited the primary contraction, the initial relation and the rebound-contraction by blocking the activity of the intrinsicnerves. 5. Phenoxybenzamine partly inhibited the initial relaxation and guane-thidine had no effect on it. ATP and ADP potentiated the initial relaxation suggesting non-adrenergic inhibitory neurones in the guinea-pig ileum. The result supports that the possibility that ATP or a related compound is a transmitter substance released by non-adrenergic inihibitory nerves. 6. It is concluded that three types of intrinsic nerves are included that three types of intrinsic nerves are included in the wall of the guinea-pig ileum. Rebound-contraction appears to be a non-nerve-mediated phenomenon. The process of the rebound-contraction may be due to intrinsic mechanism in smooth muscle cells due to the preceding hyperpolarization.