Movements of calcium (Ca) across the maternal and fetal aspects of the human placenta were investigated using the isolated placental lobule dually perfused <I>in vitro.</I> Tissues uptakes and releases of calcium were measured and the effects on calcium movements by calcium-protein binding in the perfusion fluids, (associated with extracellular pathways and non-uniform perfusion), evaluated. The effects of ouabain, dinitrophenol (DNP), and cooling on calcium movements were measured and compared to movements of Na<sup>+</sup> and K<sup>+</sup>. These indicated the presence of active transport of calcium but no evidence was obtained for Ca<sup>2+</sup>/Na<sup>+</sup> exchange. Cyclic adenosine 3', 5' -monophosphate (cAMP) levels in dually perfused tissue were measured following microwave fixation. This technique was used to measure changes in tissue cAMP production following exposure to forskolin, 3-iso-butyl-l-ethyl-xanthine (IBMX), and various fragments of both bovine parathyroid hormone (bPTH) and human parathyroid hormone-related peptide (hPTHrP). Rises in cAMP were produced by exposure to bPTH(1-34) but not hPTHrP(1-34), hPTHrP(67-86) or hPTHrP (107-138). It is concluded that calcium is actively transported across the placenta but there is no major contribution via a Ca<sup>2+</sup>/Na<sup>+</sup> exchanger. The patterns of calcium uptake as a function of perfusate calcium concentration support the evidence of other workers that extracellular pathways are present in the syncytiotrophoblast. A significant amount of passive movement of calcium may therefore take place across the perfused placenta. The 1 to 34 region of the PTH molecule stimulates the production of cAMP by the trophoblast, but there is no indication that this has any effect on transplacental Ca transport.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:387461 |
| Date | January 1994 |
| Creators | Williams, James M. A. |
| Publisher | University of Aberdeen |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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