Serum levels of neurophysin in pregnancy and in the postpartum period: relation to 17beta-estradiol levels.

Changes in serum neurophysin levels were studied in women during normal pregnancy and after delivery. Neurophysin was elevated as early as the sixth week of gestation and gradually increased until, at the latest, the twentieth week. A significant positive correlation was obtained between serum concentrations of neurophysin and those of 17beta-estradiol. In serum samples with 17beta-estradiol levels exceeding 5 ng/ml, neurophysin was consistently elevated above the normal control range. After delivery, serum neurophysin concentrations declined quite rapidly. The levels returned to those of nonpregnant women by 6 days postpartum. These results support the view that a high rate of secretion of 17beta-estradiol may be one of the factors responsible for the elevated levels of serum neurophysin in pregnancy and that this effect disappears rapidly after the disposal of estrogen, independent of the duration of the elevated estrogen levels.