Fetal Rat Parathyroids As Affected by Changes in Maternal Serum Calcium and Phosphorus Through Parathyroidectomy and Dietary Control

Bone Development and Mineral Homeostasis in the Fetus and Neonate: Roles of the Calciotropic and Phosphotropic Hormones

“…Conversely, maternal hypocalcemia may impair the forward flow of calcium from mother to fetus, and force the fetal-placental unit to upregulate the mechanisms that maintain the fetal blood calcium and placental calcium transport. Consistent with this, maternal parathyroidectomy or calcitonin infusions in pregnant rats have been shown to cause a marked increase in fetal PTH, parathyroid gland hyperplasia, and bone resorption; the skeleton is undermineralized (104,206,541,542,625). …”

“…A normal serum calcium likely requires upregulation of placental calcium transfer to maintain it, and this is supported by the observation that an acute calcium infusion caused a marked rise in serum calcium of fetuses from thyroparathyroidectomized rats, but not in fetuses from thyroidectomized rats (106). The fetal skeleton may also be compromised by resorbing itself to maintain the normal high level of calcium in fetal blood, as seen by enlargement of the fetal parathyroids (206,625), increased resorption in fetal rat bones that requires intact fetal parathyroids for it to occur (542), and reduced femur length and mineral ash content (104). But even with overt hypocalcemia throughout pregnancy, the neonate can have a perfectly normal skeleton (217).…”

“…Similarly, when pregnant rats were hypocalcemic due to thyroparathyroidectomy or calcitonin infusions, the fetal bones showed increased resorption when subsequently cultured in vitro (541,542), the fetal parathyroids enlarged (206,625), and fetal femur length and mineral ash content were reduced (104). These findings in lambs and rats are compatible with a reduction in placental calcium transport that is sufficient to delay primary mineralization of bone or induce secondary hyperparathyroidism in the fetuses, while enabling the fetuses to maintain normal concentrations of minerals within the circulation.…”

Calcium Metabolism in Newborn Animals: The Interrelationship of Calcium, Magnesium, and Inorganic Phosphorus in Newborn Rats, Foals, Lambs, and Calves

“…Several reports based on histologic observations have claimed the functional activity of the fetal parathyroid glands in humans (2, 9, 37) and in rats (2,30,33,42). In virro studies, lacking the fetal "milieu interieur" which is quite different from that found in adults.…”

The Parathyroid Glands and Phosphorus Homeostasis 12

“…Similar relations between parathyroid size and appearance and dietary phosphorus intake have been noted by others (6-10, 12, 31, 32). DISCUSSION An extensive literature has been built up concerning the effects of administered parathyroid extract (4,5,12) and the effects of parathyroid gland extirpation (1,3,12,32). These data indicate that a regular effect of administered extract is to increase renal phosphorus clearance (5,12,33).…”