OXYTOCIN-LIKE SUBSTANCE IN HUMAN PLACENTA - SEARCH FOR UTERINE CONTRACTILE SUBSTANCE

Placenta as a physiological source for oxytocic factor was implicated in our previous report, where we investigated the serum concentration of oxytocin (OT) and neurophysins during pregnancy, labor and lactatio n. The existence of immunoreactive(ir)-OT in placenta was suggested fi rst by our study of the serum concentration in the umbilical vein, art ery, and maternal circulation. The concentration of ir-OT in the place nta in the second trimester (20.8 ng/g-tissue) was 12-fold of that in the first trimester (1.6 ng/g-tissue). An immunohistochemical study on term placenta with the antiserum to OT revealed that ir-OT was mainly localized in the layer of syncytiotrophoblast. In vitro culture of tr ophoblast indicated that cycloheximide and prostaglandins (PGs) modula ted the synthesis and/or release of ir-OT in the placenta. Further, th e placental extract showed sings of mimicry of synthetic OT both in th e elution profile through a carboxymethyl cellulose column and in bioa ctivity assayed by isometric tension of uterine muscle. The bioactivit y and immunoreactivity of the extract were compared in the fractionate d eluent of the extract on a Sephadex G-25 column. The results indicat ed that the bioactivity could be parallel with the immunoreactivity as sayed by our RIA system, which was consistent with the fact that our a ntiserum neutralized the bioactivity of OT. We recently obtained a cDN A clone by immunoscreening from a human placental library, and the clo ne size was approximately 900 nucleotides. The clone was transfected i nto a Chinese hamster ovary cell line, the cultured media of which con tained the recombinant ir-OT proved by assays of both immunoreactivity and bioactivity. A search for the major contractile factor in the ini tiation of labor is in progress.