Biological Synthesis of Acetylcholine

It was demonstrated that on incubation of the human placenta at a favorable temperature, viz., 37-38°C, there is an increase of acetylcholine (AC) reaching a maximum at the 4th hour. In view of the fact that no such increase occurs during incubation, if the tissue has been soaked in alcohol, or if the eserine (Es) saline extract of the tissue is incubated, the presence of an intracellular factor (“acetylizing endoenzyme”) was postulated. It was later claimed that the action of the cholinesterase may be reverted by Es or body temperature, for the washed tissue which is almost free of the cholinesterase does not show the AC synthesis as the unwashed tissue does. Sodium fluoride, quinine, prostigmine and berberine were found to have a similar action as Es. The suggestion of the intracellular factor was soon reinforced because certain forms of physical injury, such as grinding, freezing, and air-drying, applied to the placental tissue, destroy the intracellular factor, leaving the cholinesterase intact. Such tissue does not show AC-synthesis when incubated at 37.5°C or when Es is added. Similarly, cyanide kills the intracellular factor but spares the cholinesterase, and this cyanide-treated tissue fails to produce more AC in response to Es or the incubation at 37.5°C. Now it is possible to show that both factors appear to act together for the biological synthesis of AC in the presence of Es. It is known that the pressed juice of the placenta contains the cholinesterase but not the intracellular factor, while the placental tissue which has been thoroughly washed by an intraärterial saline infusion contains chiefly the intracellular factor with only a trace of the cholinesterase.