Changes in the concentrations of corticosteroids in the blood of fetal pigs and their dams during late gestation and labor.

Abstract

Corticosteroid concentrations were determined in plasma samples obtained from chronically catheterized pig fetuses and their dams during late gestation and parturition. Mean concentrations of 14-20 ng/ml were found in fetal plasma on Days -16 to -10 before delivery and these rose to 40-60 ng/ml between Day -6 and the day of delivery. During the last 8 h of fetal life levels rose rapidly and at birth averaged 168.8 +/- 35.4 ng/ml. Maternal concentrations rose slightly during the last 3 days before delivery but increased significantly during delivery itself. Considerable variation in both the time at which the rise in fetal corticosteroids occurred and the magnitude of the rise was seen both within and between litters. Chromatographic separation indicated that the rise in fetal corticosteroids was associated with increasing cortisol concentrations rather than corticosterone. The data suggest that, while mean fetal corticosteroid concentrations increase in late pregnancy, the role of adrenal maturation of individual fetuses in the initiation of the parturition process in the pig needs further investigation.