[Study on immunoreactive oxytocin in the human placental tissue].

Immunoreactive oxytocin in the human placenta was detected by the following procedure. The fresh placenta of each trimester was rinsed with cold normal saline, then homogenized. Its supernatant was assayed for oxytocin by sensitive and specific radioimmunoassay and the dilution curve of the placental tissue was plotted on the dose response curve of synthetic oxytocin. Through carboxy methyl cellulse (CMC) column chromatography the supernatant of the homogenate was eluted and was compared with that of synthetic oxytocin. The results are as follows: 1) The placental tissue content of immunoreactive oxytocin increases from 30ng/placenta at first trimester to 4.8 micrograms at second trimester, 15 micrograms at third trimester, respectively. 2) The mean immunoreactive oxytocin concentration of 1gm of the placental tissue is 2.5ng/gm at first trimester the significantly increases to 34ng/gm at second trimester maintaining the level till third trimester. 3) The dilution curve of placental tissue nearly parallels that of synthetic oxytocin. 4) The elution curve of placental tissue through CMC column chromatography shows similar pattern compared to that of synthetic oxytocin. Though the hypothalamus and the posterior pituitary gland have been known as major sources of oxytocin, these data indicate that the placenta might be the third origin for oxytocin.