Cystine Aminopeptidase Activity in Pregnancy

Using a new method for estimation of cystine aminopeptidase (CAP) activity in maternal serum, serial CAP determinations have been performed in 7 women during normal pregnancy, in 7 patients after delivery, in 10 patients with pre‐eclampsia, in 5 patients with suspected placental insufficiency and in 4 multiple pregnancies. The results were as follows. The enzyme activity decreased slowly after delivery. The half‐life of the enzyme in maternal blood was calculated as 3–6 days except in one patient where only 20% of the enzyme activity was lost within 4 days. The decrease of CAP activity in serum after intra‐uterine foetal death was also very slow. In patients with uncomplicated mild toxaemia of pregnancy the CAP values were in the normal range. In patients with severe pre‐eclampsia the results varied. In one patient with acute severe pre‐eclampsia and a threatening eclamptic attack the CAP values were high, and this might be explained by the presence of non‐specific aminopeptidase activity in serum. In preeclampsia with associated retardation of foetal growth the CAP values were rather low, with decreasing values prior to foetal death. In patients with pronounced placental insufficiency the CAP values were consistently low, whereas high figures were often found in multiple pregnancy. The observations indicate that determination of CAP in maternal serum might be a valuable parameter in judging the condition of the placenta. However, the significance of CAP assays in assessing placental function cannot be established until the method is compared with other placental function tests on the same clinical material.