AJP - Endocrinology and Metabolism, Vol 258, Issue 4 E549-E554, Copyright © 1990 by American Physiological Society
Bioactive parathyroid hormone in pregnant rats and fetuses
A. Bourdeau, G. Manganella, C. L. Thil-Trubert, C. Sachs and G. Cournot
Centre National de la Recherche Scientifique, Universite Paris V, France.
Parathyroid function at the end of gestation (day 21) was investigated by
measuring plasma calcium (PCa), immunoreactive parathyroid hormone (iPTH),
bioactive parathyroid hormone (bioPTH; cytochemical bioassay), and bone
histology in intact and thyroparathyroidectomized (TPTX; day 12, ether
anesthesia) rats and their fetuses. In pregnant intact rats, PCa was
significantly lower, and iPTH, bioPTH, and osteoclast number were higher
than in nonpregnant rats. In fetuses, PCa was higher than maternal PCa and
correlated with fetal bioPTH. TPTX suppressed maternal bioPTH and decreased
iPTH and osteoclast number, whereas fetal iPTH and bioPTH were decreased
with no change in osteoclast number. Fetal PCa was near normal and was
correlated with maternal PCa but not with fetal bioPTH. The fetomaternal
calcium gradient was maintained and even increased. This study shows that
there is maternal physiological hyperparathyroidism and functional fetal
parathyroid glands at the end of gestation in the rat. Parathyroid hormone
does not seem to be responsible for maintaining the high fetomaternal
calcium gradient in TPTX animals.
