Location and activities of acetylcholinesterase and butyrylcholinesterase in the rat and human placenta.

The location and physiological functions of acetylcholinesterase and butyrylcholinesterase in the placenta are still debated. In the present study the activities of both enzymes were studied histochemically in the rat and human placenta, using an optimized Karnovsky/Roots method. Additionally, they were measured biochemically. Acetylcholinesterase was active in the syncytiotrophoblast, cytotrophoplast cells and the visceral and parietal yolk sac epithelial cells of the rat (n = 10) and in the syncytiotrophoblast, cytotrophoblast cells, endothelial cells and the media of fetal blood vessels of the human placenta (n = 9). Butyrylcholinesterase could not be detected histochemically. Biochemically measured levels at certain developmental stages of the placenta revealed maximum acetylcholinesterase activity in the 8th week p.m. human placentae (102.9 nmol.min-1 per mg protein), 35% lower activity in the 12th week p.m., and minimum (44.1 nmol.min-1 per mg protein) in term placentae. In contrast, maximum butyrylcholinesterase activity was measured in week 12 p.m. (106.9 nmol.min-1 per mg protein). In rat placentae, butyrylcholinesterase activity on gestational day 21 reached 150% of the level on gestational day 16. Acetylcholinesterase activity remained constant. In placentae of pre-eclamptic patients, acetylcholinesterase and butyrylcholinesterase activities were found to be increased by 16% and 45%, respectively. The results suggest that placental acetylcholinesterase can no longer be considered as derived from maternal blood, but is primarily located within rat and human placental tissue.