STIMULATION OF OVINE PLACENTAL CALCIUM TRANSPORT BY PURIFIED NATURAL AND RECOMBINANT PARATHYROID HORMONE‐RELATED PROTEIN (PTHrP) PREPARATIONS

Abstract

SUMMARYPerfusion in situ of the placenta of previously thyroparathyroidectomized fetal lambs has been used to compare the ability of various forms of parathyroid hormone-related protein (PTHrP) to stimulate placental calcium transport. Whereas PTHrP (1-34) was without effect, PTHrP (1-141) was active but usually after a delay of up to 1 h, in common with the effect noted when using extracts of fetal parathyroid glands. In contrast, PTHrP (1-84) and PTHrP (1-108), tended to show a more rapid stimulatory action. It is suggested that post-translational processing of PTHrP (1-141) may occur as an activating step in the placenta in vivo.

Immunochemical Detection of Parathyroid Hormone-Related Protein in the Saccus Vasculosus of a Teleost Fish

“…In fetal sheep PTHrP is responsible, at least in part, for maintaining the differential gradient between high fetal serum calcium and that of the maternal circulation (Rodda et al, 1988;Abbas et al, 1989;Care et al, 1990). A midmolecule fragment of PTHrP was suggested to be responsible for placental transport of calcium in sheep (Care et al, 1990), a region which appeared to be present in Sparus saccus through interaction with antibody specific to the midmolecule 50-69 residues.…”

The role of parathyroid hormone‐related protein in calcium homeostasis in the fetal pig

“…We have no direct evidence that PTHrP of parathyroid origin regulates placental calcium transport in the pig, as it does in the sheep (Rodda et al 1988;Abbas, Pickard, Rodda, Heath, Hammonds, Wood, Caple, Martin & Care, 1989;Care, Abbas, Pickard, Barri, Drinkhill, Findlay, White & Caple, 1990), but PTHrP derived from the placenta itself may have a local action on calcium transport to the fetus. Thyroparathyroidectomy of the ovine fetus, with thyroxine replacements, results in reversal of the placental calcium gradient (Care, Caple, Abbas & Pickard, 1986).…”

Fetal parathyroids are not required to maintain placental calcium transport

“…The present studies were carried out in intact fetal mice that lacked parathyroids from conception and whose mothers were heterozygous for the same genetic defect. The studies in fetal lambs involved a surgical procedure on the lambs, followed by later removal of the fetus and subsequent perfusion of the isolated placenta in situ (4,20). Because plasma PTHrP measurements were not carried out for these thyroparathyroidectomized lambs, it is not known whether the reduction in placental calcium transfer was accompanied by a reduction in plasma PTHrP.…”

“…Nonspecific staining was blocked with normal goat serum diluted in PBS/NBS. Primary antibody was rabbit anti-PTHrP [1][2][3][4][5][6][7][8][9][10][11][12][13][14] (18), diluted 1:200 in PBS/NBS, and applied at 20°C for 60 minutes (this step was omitted from control sections). Biotinylated secondary antibody was goat anti-rabbit (Vector Canada, Burlington, Ontario, Canada), diluted in PBS/NBS, and applied at 20°C for 30 minutes.…”

“…Regarding the latter question, indirect evidence suggests that the parathyroids are a major source of fetal blood PTHrP in sheep (4,5), but direct confirmation of this hypothesis is lacking. In fact, a detailed study of the parathyroids of fetal rats found abundant PTH mRNA but no detectable PTHrP mRNA (10), suggesting that the fetal parathyroids are not the source of PTHrP in the circulation of that species.…”