抄録
1) The transmembrane potentials and the tension were recorded from strips of the rat uterus in the later middle period of pregnancy to elucidate the mechanism of action of oxytocin.
2) The spontaneous contraction of the uterine muscle was very irregular and weak in this period. Application of pitocin to the muscle, however, caused first a strong and tonic contraction and next a series of rhythmical contractions. The tonic contraction was accompanied not only with an increase in the muscle tonus but also with a long series of tetanic discharges.
3) The maximum frequency of discharge increased under the effect of pitocin given in a low concentration, but decreased in a high concentration despite a strong tension development. In the latter condition all penetrated cells discharged syntonically in regular rhythm, and pitocin seems to strengthen the mutual and functional connection between each two myometrial cells.
4) Pitocin caused a decrease in size of both resting and active membrane potentials. The decrease may be attributable partly to the tension development on the muscle, but partly to the direct action of pitocin on the membrane, because the membrane potentials decreased even in a muscle unfixed and kept isotonic.
5) The action potentials appeared rather flat in shape under the effect of pitocin, but the spikes became uniform both in height and shape. The action potentials recorded after the removal of pitocin were, on the other hand, very irregular in shape, height and rhythm, including a twin or a triplet spike occasionally between discharges. These facts also support the view that pitocin acts strongly on the muscle cells by strengthening their functional bindings.
