Direct evidence of a parathyroid related protein gradient between the mother and the newborn in humans

Abstract

Umbilical cord plasma has increased parathormone (PTH)-like bioactivity in comparison with that in maternal plasma, but suppressed PTH levels. Previous attempts to detect elevated levels of PTHrP(1–34) in the umbilical cord were unsuccessful, whereas PTHrP was detected by immunohistochemistry in both fetal parathyroid glands and placental membranes. At the time of delivery, plasma samples were drawn simultaneously from 47 normal mothers (mean age, 26 years) and from the umbilical cord of 25 female and 22 male newborns and assessed for calcium adjusted for albumin, magnesium, creatinine, intact PTH and PTHrP. PTHrP was measured using a new 2-site immunoradiometric assay recognizing separately 1–40 and 60–72 residues with a sensitivity of 0.3 pmol/1. Mean (± S.D.) plasma calcium values were 2.35 ± 0.10 in the mothers versus 2.63 ± 0.12 mmol/1 in the newborns ( P < 0.001). PTH values were significantly higher in the mothers, as expected (22.3 ± 14.8 vs. 6.2 ± 0.9 pg/ml). In contrast, PTHrP values were significantly higher in the newborns (1.50 ± 0.39 versus 0.84 ± 0.28 pmol/1, P < 0.001). Only 1/47 mother had a PTHrP level higher than her child (0.9 vs. 0.8 pmol/1). Only 10/47 mothers had PTHrP higher than 1 pmol/1 whereas only 1/47 newborn had a value below 1 pmol/1. There was no correlation between Ca and PTHrP in either group. Serum creatinine values were all within the normal range. Serum magnesium levels were not different between the mothers and the children. In confirmation with previous animals studies, these results show evidence for secretion of PTHrP in human newborns that might explain the active placental transfer of calcium to maintain the fetus relatively hypercalcemie.