Abstract
We described before measurement of plasma oxytocin levels by a specific and sensitive radioimmunoassay method.
Plasma oxytocin concentrations, measured in 111 pregnant patients, were 6.1 ± 1.9 pg/ml in the first trimester (0-16 weeks), 14.7 ± 7.3pg/ml in the second trimester (17-28 weeks), 28.4 ± 14.5pg/ml in the third trimester (29 weeks -), 29.8 ± 7.1pg/ml in the first stage of labor and 33.1 ± 12.1pg/ml in the third stage of labor, respectively. The levels increased during pregnancy and labor and decreased to 18.7 ± 9.0pg/ml on the second day and to 4.3 ± 2.7pg/ml on the seventh day after labor. The levels increased from 3.7 ± 1.7 pg/ml to 6.2 ± 3.7pg/ml during lactation.
In 42 women, 24 labors at term were induced by the intravenous administration of prostaglandin F2α. The plasma oxytocin levels were increased from 18.3 ± 9.6pg/ml to 24.4 ± 9.3pg/ml in cases of successful induction delivery and from 12.3 ± 3.2pg/ml to 19.7 ± 12.0pg/ml in unsuccessful cases by a 90 minute infusion of prostaglandin F2α.
The correlation coefficient (r) between the elevated levels of plasma oxytocin and the administered doses during the 90 minute infusion of prostaglandin F2α was 0.4355 (P<0.05).
From the results described above, it may be assumed that oxytocin plays an important role in spontaneous labor.
