Fetal and Placental Phosphate Metabolism
Few data have been reported about fetal phosphate and placental phosphate transfer. In most cases, the observations on phosphate were included in studies involving calcium-phosphate metabolism because the homeostasis of these two minerals is intimately linked and regulated. Thus, calciotropic hormones were viewed as the main regulators of phosphate metabolism in the fetus. This chapter focuses on the partial knowledge obtained in few species where attempts were made to change the phosphorus retention by the fetus. As accumulation of phosphorus by the fetus is dependent on the placental transport of the mineral, the control of this process is of major importance for fetal phosphate retention. The mechanisms implicated in the placental transfer of phosphorus are poorly understood, and investigations are complicated by the presence of different types of placentation in mammals. Progress should be obtained in models using hemochorial placentas as in humans; in such structures investigations on the cellular mechanisms involved in phosphate transport would be fruitful. Although the net flux of molecules across the placenta depends on blood flow, this parameter was neglected in most in vivo studies. The role of maternal hormones and fetal hormones on the placental transfer of phosphorus is not clear and requires further investigation.