The Origin of Human Pregnancy Serum Oxytocmase

Abstract

Serial electrophoretic experiments concerning serum and placental oxytocinases were carried out with a direct staining method for cystine aminopeptidase activity. The pregnancy serum oxytocinase and the lysosomal oxytocinase in human placenta shared the same enzymatic characteristics, with regard to heat resistence, sensitivity to L-methionine inhibition and electrophoretic pattern. These similarities suggest that the possible site of production of pregnancy serum oxytocinase is the lysosomes of the placenta, from which the enzyme is released into maternal circulation during pregnancy. Absence of oxytocinase activity in fetal serum indicates that this enzyme does not leak into fetal circulation. The physiological significance of oxytocinase was discussed with special reference to the oxytocin-oxytocinase equilibrium during pregnancy and labor.