HUMAN PLACENTAL AND BOVINE CORPORA LUTEAL OXYTOCIN

Abstract

Extracts of human placental and pregnant bovine luteal tissues contained immunoreactive oxytocin (“contractin factor”) which inhibited the in vitro mouse uterus responsiveness to the relaxation normally observed upon addition of relaxin (RXN). This “contractin factor” (CF) eluted post-6,000 mol wt RXN on a Sephadex G-50 column and was further purified on Sephadex G-25. Immunoreactive oxytocin was detected by RIA in both the placental (3 ng/mg by weight) and luteal (11.0 ng/mg by weight) G-25 CF fractions. A good correlation was observed between the bioassayable and immunoreactive oxytocin (CF). One milliunit of either oxytocin standard (1.68 ng) or 0.9 mU CF was required to reinitiate uterine contractions which were first inhibited by 1.2 U of RXN. The further addition of 100 U RXN would not reinitiate contractions. The uterine stimulating activity of oxytocin and CF could be partially inhibited by a monoclonal antibody to oxytocin, and the human and bovine G-25 CF eluted on a HPLC column at a fraction corresponding to oxytocin.