Effects of Oxytocin and Prostaglandin F2α on Pregnant Human Myometrium Recorded by the Single Sucrose‐Gap Method –Comparison of an in vitro Experiment and an in vivo Trial–

Effects of oxytocin and prostaglandin F2α on the electrical and mechanical activities of the pregnant human isthmic myometrium were investigated by a single sucrose-gap method. Human isthmic myometrium obtained at the late stage of gestation showed plateau- and spike-type action potentials. Both oxytocin and PGF2α potentiated the spontaneous contractions by affecting the plateau part of action potentials; spike-type configurations became plateaus. However, high dosages of both drugs were required to obtain consistent excitatory effects in vitro. In obstetric practice, on the other hand, uterine contractions can be induced by low-doses of oxytocin or PGF2α. These results suggest that both oxytocin and PGF2α can increase spontaneous contractions by enhancing plateau potentials in vitro. However, the pharmacological application of oxytocin or PGF2α might only play a triggering role in uterine contractions at induction or augmentation of labor, and complex interactions might be involved in the initiation and potentiation of contractions in vivo.