Studies on the placental transfer of phosphate in the guinea pig. III. Phosphorus compounds in the placenta and their uptake of radioactive phosphorus.

Abstract

Summary.Determinations of the various phosphorus fractious in the guinea pig placenta in a series of experiments on the placental transfer of phosphate have shown that the orthophosphate concentration is very high in the placental tissue as compared with the maternal and foetal plasma. The concentration increases slowly from the 29th to the 59th day of gestation and may decrease thereafter.Thirty minutes after intravenous injection of radioactive phosphate into the mother the orthophosphate in the placenta has reached a specific activity of one third of that of the inorganic phosphate in the maternal plasma. It has the highest specific activity of the placental phosphorus fractions.Adenosine diphosphate and triphosphate are found in approximately the same concentrations as in the uterine muscle during pregnancy in the rat, the rabbit and the human. The labile phosphorus of these compounds is in equilibrium with the orthophosphate with regard to radioactive phosphorus.Glucose‐1‐phosphate is present in a low concentration, but it acquires a high relative specific activity. More glucose‐6‐phosphate is present, but with a low relative specific activity.The inorganic phosphate in the foetal plasma obtains in thirty minutes a specific activity of about half that of the placental orthophosphate.