Circulating levels of biologically active and immunoreactive intact parathyroid hormone in human newborns.
We evaluated circulating levels of biologically active and immunoreactive intact parathyroid hormone [iPTH-(1-84)] in 47 newborns at birth and eight hypocalcemic preterm infants during the first 10 d of life. Use of two sensitive detection systems, the cytochemical bioassay and an immunoradiometric assay specific for intact parathyroid hormone, enabled us to compare plasma concentrations of PTH-like bioactivity (bioPTH) and iPTH-(1-84). Mean umbilical venous plasma bioPTH was elevated in nondiabetic term and preterm newborns [22.5 +/- 3.1 (+/- SEM) and 15.8 +/- 2.5 ng-equiv/L, respectively] compared with normal adult subjects (9.8 +/- 2.6 ng-equiv/L; p less than 0.01). Umbilical bioPTH was suppressed in five term infants of diabetic mothers (2.6 +/- 0.4 ng-equiv/L). In contrast, iPTH-(1-84) was low in term and preterm nondiabetic infants' and term infants of diabetic mothers' umbilical samples (5.4 +/- 1.5, 4.3 +/- 1.5, and 2.4 +/- 1.0 ng/L, respectively). Umbilical venous bioPTH was highly correlated with the magnitude of the transplacental calcium gradient (r = 0.90; p less than 0.05). In eight preterm infants studied longitudinally, by 24-36 h of life, declining plasma total and ionized calcium (1.71 +/- 0.04 and 0.78 +/- 0.03 mmol/L, respectively) were accompanied by a significant rise in both bioPTH (41.2 +/- 6.3 ng-equiv/L) and iPTH-(1-84) (56.3 +/- 11.6 ng/L). These data indicate that the 3rd trimester fetoplacental circulation contains levels of bioPTH several-fold higher than those of immunoreactive intact hormone. We also conclude that even hypocalcemic preterm newborn infants can significantly elevate circulating levels of PTH.
Rubin
L P
LP
Department of Pediatrics and Medicine, Harvard Medical School, Boston, Massachusetts.
Posillico
J T
JT
Anast
C S
CS
Brown
E M
EM
D000328:Adult; D002118:Calcium / Q000097:blood; D005260:Female; D005312:Fetal Blood / Q000378:metabolism; D006801:Humans; D006996:Hypocalcemia / Q000097:blood; D015592:Immunoradiometric Assay; D007231:Infant, Newborn / Q000097:blood*; D007234:Infant, Premature; D008297:Male; D010281:Parathyroid Hormone / Q000097:blood*; D011247:Pregnancy; D011254:Pregnancy in Diabetics / Q000097:blood; D012016:Reference Values
D010281:Parathyroid Hormone; D002118:Calcium