OXYTOCIC ACTIVITY OF BLOOD IN PARTURIENT AND LACTATING WOMEN

Abstract

The Bristol procedure was used for the extraction of oxytocin from the blood taken from healthy pregnant women during the last trimester of pregnancy and from women during labor. Both oxytocin and oxytocic substance (O.S.) were found in the plasma extracts. The levels of oxytocin in the blood were the same during labor as during late pregnancy, but more O.S. was present in early labor than during pregnancy. The concentration of O.S. was higher in early labor than in late labor. There were no differences in the oxytocic activity (O.A.) of blood samples drawn (a) during and between uterine contractions, and (b) from primiparous and multiparous women. Precautions were taken to exclude the possibility that potassium, 5-hydroxytryptamine, acetylcholine and plasma kinin in the acetone extracts might be acting as interfering substances in the assays. The extracts were assayed on the isolated sensitized rat uterus, by the use of both the superfusion and classic methods. The results obtained suggest that O.S., rather than oxytocin, may be involved in the mechanism of onset of parturition. Samples of blood taken from healthy lactating women who had babies 1-5 months old were assayed for oxytocin as described. Both oxytocin and oxytocic substance contributed to the oxytocic activity of these extracts. The levels of O. A , oxytocin and O.S. were determined in the extracts of blood samples taken immediately before and during suckling from; 1) women who were wholly, and those who were partly, breast-feeding their infants; 2) primiparous and multiparous women, and 3) women who has been lactating for less than six weeks, and those lactating for more than six weeks. There was no difference between the blood oxytocin levels before and during suckling, but the levels of O.A., oxytocin and O.S. were higher in nursing women than in those who were not nursing. There were no statistical differences in the levels of O.A., oxytocin and O.S. in blood taken from women who were wholly breast-feeding and those who were complementing their babies'' diets, nor were there any differences in the levels of these 3 substances between primiparous and multiparous women.