The stability and short-term fluctuation in serum oxytocinase activity in pregnancy.

Maternal serum samples obtained from 123 normal pregnant women between 28 and 40 weeks gestation were analysed for oxytocinase (EC 3.4.11.3) activity using s-benzyl-1-cysteine-4-nitroanilide as substrate. Oxytocinase activity was found to be stable at varying temperatures, with a mean co-efficient of variation of 5.0%. The short-term fluctuation of oxytocinase activity had a mean coefficient of variation of 3.6%. There is no suggestion of a "pulsatile" release of oxytocinae from its placental origin.