Oxytocin content of human fetal pituitary glands

Seventeen human fetal and neonatal pituitary glands were removed at necropsy, and analyzed for oxytocin content by a specific and sensitive radioimmunoassay, after homogenization in 0.4M acetic acid. Serial dilution of the pituitary extract showed parallelism with the oxytocin standard curve on the radioimmunoassay. Column chromatography of the pituitary gland extract gave a single peak of immunoreactive oxytocin as determined by the radioimmunoassay. In eight fetuses, 14 to 17 weeks' gestation, pituitary gland oxytocin was 10.2 +/- 5.9 ng/gland (mean +/- SE), whereas an 18-week fetus had 5.8 ng of oxytocin per gland. Pituitary gland oxytocin content increased to 38.4 ng/gland in a 20-week fetus removed at hysterectomy, and 31.6 ng/gland in a 26-week fetus. Fetal pituitary gland oxytocin values were 22.1 ng/gland and 57.0 ng/gland at 32 weeks and increased significantly to 544.3 +/- 33.8 ng/gland in 1- to 5-day-old term newborn infants (n = 3). However, a 13-day-old term newborn infant had 3.7 ng of oxytocin per pituitary gland. The increased pituitary gland oxytocin content with advancing gestation was due to a significant increase in oxytocin concentration rather than to an increase in the weight of the pituitary gland. The findings indicate that oxytocin is present in fetal pituitary glands as early as 14 to 17 weeks' gestation and increases at term to 50 and 13 to 14 times more than in early midtrimester and early third-trimester pregnancy, respectively.