High α‐amylase activity in the syncytiotrophoblastic cells of first‐trimester human placentas
The syncytiotrophoblastic brush border of the human placenta forms the maternal‐fetal interface and is an important determinant of placental function. Electron micrographs of fresh brush border preparations isolated from first‐trimester human placentas showed membrane vesicles, open‐ended microvilli, and numerous glycogen particles. Analysis of the microvillar membranes for several plasma and intracellular membrane markers showed a high degree of purification, comparable to the results reported for the isolation of microvilli from full‐term human placentas. The microvillar preparations from first‐trimester placentas, however, also contained the enzymes necessary to synthesize and degrade glycogen. The degradation resulted in the accumulation of maltotriose and maltotetraose, apparently due to the action of a liver‐type α‐amylase. The occurrence of this enzyme and the enzymes for synthesizing glycogen in this brush border fraction is probably associated with the necessity for an extremely active glucose transport and liver‐like storage system within the fetal tissue at this fetal‐maternal membrane interface. Copyright © 1983 Alan R. Liss, Inc.