Phosphate metabolism and foetal growth in the rat. II. Net transfer of 31P and 32P inorganic phosphate from the maternal plasma to the normal foetus.
Net transfer of 31P and 32P inorganic phosphate from the maternal plasma to the rat foetus has been studied after intraperitoneal injection of [32P] ortho-phosphate in primigravid females at the 12th day or later stages of gestation. The concentration per unit weight of foetus of the inorganic phosphate (P1) fraction increases markedly with increasing foetal weight; labelling data [inverse relationship between P1 concentration and specific activity, absence of precursor/product relationship between P1 and acid-soluble organic-bound phosphates (POAS)] show this increase to result in part from the formation of a relatively inert metabolic pool, presumably in mineralized tissue. The foetal concentrations of calcium and inorganic phosphate show a strong positive correlation, both increasing markedly with foetal weight. The progressive accumulation of calcium does not, however, account entirely for the rising concentration of inorganic phosphate. The concentration per unit weight of foetus of the POAS fraction remains stable for foetuses smaller than 2 000 mg. In heavier foetuses (greater than 2 000 mg) the POAS concentrations are, with an abrupt transition, distinctly lower, rising however slightly with increasing foetal weight. The concentration per unit weight of foetus of the acid-insoluble organic-bound phosphate (POAIS) fraction decreases slightly with increasing foetal weight. The label uptake per unit weight of foetus of both POAS and POAIS fractions is negatively correlated with increasing foetal weight. The amount and label uptake per whole foetus of the P1, POAS and POAIS fractions are positively correlated with increasing foetal weight. Phosphate transfer to the foetus increases continuously, being maximal at or near birth.
D000818:Animals; D002118:Calcium / Q000378:metabolism; D005260:Female; D005333:Fetus / Q000378:metabolism*; D008431:Maternal-Fetal Exchange; D010710:Phosphates / Q000378:metabolism*; D011247:Pregnancy; D051381:Rats
D010710:Phosphates; D002118:Calcium