Oxytocinase in plasma and placenta in normal and prolonged labour.

In prolonged labour (dystocia) the level of activity of the enzyme oxytocinase is increased in the plasma and decreased in the placenta; the ratio of its activity in the placenta to that in plasma is less than half that found in normal labour. A possible explanation is that oxytocinase is derived mainly from the placenta and that during prolonged labour the enzyme escapes into the maternal blood stream.