[A basic study on the initiation of human parturition--contribution of amniotic fluid and fetus to the initiation of human parturition].

In order to clarify the mechanism of initiation of human parturition, the relationship of amniotic fluid and fetus to prostaglandin synthesis was investigated. Phosphatidylinositol (PI) in amniotic fluid and phospholipase C (PLase C) activity in amniotic fluid, amnion tissue and neonatal urine were measured. The results are as follows. PI in amniotic fluid began to increase from around 30 to 36 or 37 weeks of gestation, and then gradually decreased toward term. PLase C activity in amniotic fluid was demonstrated. The activity was low before 30 weeks of gestation, but gradually increased toward term. PLase C activity in 105,000 X g supernate of amnion tissue homogenate was 43 fold higher than that in amniotic fluid. High PLase C activity was demonstrated in neonatal urine, which was 58 fold higher than that in amniotic fluid. The molecular weight of PLase C from neonatal urine was estimated to be 33,000 daltons. PLase C activity in neonatal urine has enough activity to produce arachidonic acid in amniotic fluid. It was concluded that the fetus relates to the onset of labor by producing arachidonic acid in amniotic fluid as a result of the reaction between PI from the lung and PLase C from the urine.