Localization and concentrations of beta-endorphin and beta-lipotrophin in human placenta.

Immunohistochemical staining of placental tissue for beta-endorphin immunoreactivity was positive in the syncytiotrophoblast in both early and term pregnancy. Cation-exchange liquid chromatography and radioimmunoassay revealed peaks of beta-endorphin and beta-lipotrophin and a third immunoreactive peak of unknown nature. The concentration of beta-endorphin was higher in the placental tissue than it was in the maternal or cord plasma. beta-Lipotrophin was not detected in all placentae studied. We did not find any effect of gestational age on tissue concentrations of endorphins in the placenta, nor was there any significant difference in the placental endorphin content between placentae collected at elective caesarean section before labour and after spontaneous vaginal delivery.