Placental Esterases.

Since the placentas of man and animals lack innervation 1 , it is of considerable interest that acetylcholine 2 3 4 and a cholinesterase 5 have been identified in human placentas. Torda found that cholinesterase activity of human placentas at full term approximated one tenth of that of pig's pyloric mucosa. Ord and Thompson 6 reported that homogenates of fresh placentas hydrolysed acetylcholine, benzoylcholine and acetyl β-methylcholine, but that homogenates prepared from perfused placentas possessed much less activity toward benzoylcholine. According to the criteria of Mendel, Mundell and Rudney 7 , these results indicate that both acetylcholinesterase and serum cholinesterase are present in the placenta. Further evidence of the occurrence of cholinesterases was the inhibition of the enzymes by di-isopropyl fluorophosphate in a concentration similar to that required to inhibit the cholinesterases of brain. Wen, Chang and Wong 8 devised a method, which they believed demonstrated the activity of acetylcholine in tissue sections, by means of which they identified large amounts of acetylcholine in the syncytial trophoblast of the chorionic villi and in the intervillous space of the human placenta. With the recent development of several histochemical methods for the demonstration of esterases, it seemed advantageous to explore the placenta by these means and with the use of inhibitors to differentiate between various enzymes of the esterase groups. From an examination of a normal human placenta of 10 weeks' gestation age 9 10 , it was found that with the method for esterase of Barrnett and Seligman 11 on unfixed frozen sections there is an intense reaction in the trophoblast clothing the chorionic villi, involving mainly the syncytium. With the esterase method of Nachlas and Seligman 12 , however, carried out on sections of acetone-fixed, paraffin-embedded material, the trophoblast showed no reaction.