High alpha-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 alpha-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.