An ultrahistochemical study of the distribution of acid and alkaline phosphatases in placentae from normal and complicated pregnancies

The subcellular localisation of acid and alkaline phosphatase was studied in the trophoblast of placentae from both normal and complicated pregnancies. In placentae from uncomplicated pregnancies the number of trophoblastic acid phosphatase containing organelles decreases progressively as gestation proceeds whilst alkaline phosphatase activity, although abundant at term, could not be demonstrated during the early stages of pregnancy. The acid phosphatase containing organelles are of two types; one is a small round body which is probably a lysosome whilst the other is a multivesicular body. The alkaline phosphatase is distributed mainly on the syncytial microvilli and plasma membrane. It is suggested that the marked lysosomal activity during early pregnancy is related to the architectural refashioning of the placenta during this period and that there are two phosphatase linked transfer systems in the trophoblast, one dependent upon acid phosphatase containing multivesicular bodies and being utilised during early pregnancy and the other reliant upon alkaline phosphatase and dominating during the second half of gestation. In placentae from prolonged pregnancies there is a further decrease in trophoblastic acid phosphatase and, usually, a continuing increase in alkaline phosphatase activity. In placentae from babies of low birth weight this trend is sometimes reversed and alkaline phosphatase activity either disappears or its reaction product diffuses throughout the syncytium; this is usually accompanied by a marked increase in the number of acid phosphatase containing multivesicular bodies. Placentae from women with pre eclampsia show no loss of alkaline phosphatase activity but are characterised by an increased number of lysosomal bodies.