[Prostaglandin Production by the human placenta using a superfusion technique (author's transl)]

In order to clarify the onset mechanism of labor, we studied the prostaglandin production in human placenta tissues of different stage using a superfusion technique. 1) The placenta obtained at Cesarean section before the onset of labor (A): (1) In the control, the production of prostaglandins was not distinctly changed. (2) Administration of arachidonic acid increased gradually the production of PGs. PGs production showed the maximum values at 50-60 minutes fraction of the superfusion. Throughout the experiment, PG production became vigorously active. (3) Administration of oxytocin increased the production of PGs, too, in particular PGE2 and PGF2 alpha. 2) The placenta obtained at Cesarean section during delivery (B): (1) In the control, the production of PGs was not distinctly changed. (2) Administration of arachidonic acid increased the production of PGE2 and PGF2 alpha, but the production of PGs was lower as compared with (A). PGE1 did not change. (3) Oxytocin had no effect on the production of PGE1 and PGE2, but the production of PGF2 alpha showed the maximum values at 50-60 minutes fraction. 3) The delivered placenta (C): (1) In the control, the production of PGs was not distinctly changed. (2) Administration of arachidonic acid increased the production of PGs. (3) Oxytocin had no effect on the production of PGs. On the basis of these data, it may be appropriate to conclude as follows: The enzyme which has a high ability to produce PGs exists in the placenta before the onset of labor. But the enzyme keeps the resting condition by the some inhibiting factor of PG production. During delivery, the PG production by the placenta fell. This result means that the strong ability of the production of PGs by the placenta at this stage is not necessary. After the delivery, the production of PGs by the delivered placenta is unnecessary. It is substantiated Kato's theory which PGE is primarily involved in the onset of labor that the production ability of PGE was recognized only in the placenta of before the onset of labor. It is interesting that administration of oxytocin increased the production of PGF2 alpha and they are similar for the contraction-substance of uterus.