The effects of prostaglandin E1 and F2 alpha on the mechanical and electrical responses of circular strips dissected from various parts of the guinea-pig stomach were examined. Prostaglandin E1 induced the tonic contraction without an inhibition of the phasic contraction in lower parts of stomach. The amplitude of tonic contraction decayed along with greater curvature of the stomach, that is, it was largest in pylorus region and smallest in upper corpus. Furthermore, the tonic contraction increased depending on concentrations of prostaglandin E1. When a longitudinal muscle layer was removed from the circular strips, the tonic contraction disappeared. On the other hand, prostaglandin E1 or F2 alpha consistently induced an increase in the resting tone and the phasic contraction in longitudinal strips of all parts of stomach. Simultaneous recordings of the electrical and mechanical activities showed a correlation between membrane depolarization and tonic contraction induced by prostaglandin E1. Above results were not affected by nerve-blocking agent, atropine or tetrodotoxin. Thus it is suggested that the tonic contraction in circular strips induced by prostaglandin E1 is closely related to the longitudinal tonic contractions.
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