在妊娠期间,母体血清中出现一种能灭活催产素的氨基肽酶,称之为催产素酶。男性和非妊娠妇女循环中催产素酶水平极低,妊娠期呈指数性升高,到妊娠末或近于分娩时达最高浓度,产后迅速消失。该酶在维持和终止妊娠中起关键作用。虽然通常认为胎盘是该酶的主要来源,但在其它组织如肝脏、肾脏、胰腺、乳腺、子宫、卵巢、垂体和下丘脑也存在此酶的活性。在胎儿血里仅发现低水平的催产素酶活性,这意味该酶不是来源于胎儿。 During pregnancy, there is an aminopeptidase that can inactivate oxytocin in maternal serum, called oxytocin. Cyclic oxytocin levels in both male and nonpregnant women are very low and rise exponentially during pregnancy, reaching the highest concentrations at or near the end of pregnancy, and disappear quickly after giving birth. This enzyme plays a key role in the maintenance and termination of pregnancy. Although it is generally accepted that the placenta is a major source of this enzyme, this enzyme is also present in other tissues such as the liver, kidney, pancreas, breast, uterus, ovary, pituitary and hypothalamus. Only a low level of oxytocin activity is found in fetal blood, which means that the enzyme is not derived from the fetus.