Changes in beta-endorphin in fetal membranes and placenta in normal and pathological pregnancies

Several studies indicated that trophoblast tissue synthesizes pro-opiomelanocortin-related peptides. These peptides are also present in amniotic fluid, but their origin remains unknown. The present study evaluated the presence of and the possible changes in beta-endorphin (beta-EP) in amnion and chorion during pregnancy, at parturition and in spontaneous abortion. Amnion, chorion and placental tissues were isolated and homogenized from a total of 46 pregnant women between 4th and 42 th week of pregnancy. Beta-EP was separated on a Sephadex G-75 column and measured by RIA with specific antiserum. The identity of the endogenous opioid with its corresponding reference molecule was confirmed by high performance liquid chromatography. In all tissues, the concentration of beta-EP in the first trimester was significantly higher than in the second trimester. A negative correlation between opioid levels and gestational age was observed in the first two trimesters. At delivery, the beta-EP content of all tissues was greater than in the second trimester. In tissues collected at term, in the absence of labor, beta-EP levels were very low in comparison with those collected after vaginal delivery. Low beta-EP contents were found in membranes collected from spontaneous abortion in 1st trimester. From these data one can surmise the existence of a local endogenous opioid system in fetal adnexes. This system seems sensitive to the stress of vaginal delivery and could be involved in the mechanisms leading to spontaneous abortion.