Oxytocinase activity in human amniotic fluid and its relationship to gestational age

Oxytocinase (EC 3.4.11.3) activity in amniotic fluid samples obtained from 200 normal pregnant women (mean age, 28 years) between 14 and 40 weeks of gestation and during active labor was assayed using S-benzyl-L-cysteine-p-nitroanilide (BCN) and L-leucine-p-nitroanilide (LN) separately as substrates. With both substrates, amniotic fluid oxytocinase activity correlated inversely with gestational age; the level of the enzyme, which was highest in early pregnancy, decreased exponentially to a minimum near term and during labor. However, whether oxytocinase activity in the amniotic fluid is of any significance for the maintenance and/or termination of pregnancy remains to be established.