Immunoreactive oxytocin in human placental tissue.

: Immunoreactive oxytocin was detected with the aid of specific and sensitive assay in a supernatant obtained after homogenization of human placenta. It was found that: 1. The content of immunoreactive oxytocin increased from 30 ng per placenta at first trimester to 4.8 micrograms at second trimester and 15 micrograms at third trimester; 2. The mean immunoreactive oxytocin concentration in 1 g of the placental tissue was 2.5 ng g-1 at first trimester and then it significantly increased to 34 ng g-1 at second and third trimester; 3. The dilution curve of placental tissue was nearly parallel to that of synthetic oxytocin; 4. The elution curve of placental tissue through CMC column chromatography showed similar pattern with that of synthetic oxytocin. Though the hypothalamus and the posterior pituitary have been known as major sources of oxytocin, these data indicate that the placenta might be the third source of this hormone.