A correlative review of acetylcholine synthesis in relation to histopathology of the human syncytiotrophoblast.

Acetylcholine (ACh) is localized in the syncytiotrophoblast layer of the human placental villous tissue. An attempt was made to correlate the ACh synthesis in different pathological placentas with the histopathology of the syncytiotrophoblast available in the literature. The ACh synthesis was estimated by 'in vitro' incubation of the placental tissue. Full-term (36-38 weeks) vaginally delivered pathological placentas and hydatid moles (28 weeks) were compared with normal placentas of the same age. The results suggested that: ACh synthesis is normal in states with normal syncytiotrophoblast (e.g., healthy greater than 42 week placenta, placenta praevia, twins, and hydramnios); high ACh synthesis is correlated with hormonal and immunological changes (e.g., diabetes mellitus and Rh-incompatibility); low levels of ACh synthesis occur in states with moderate syncytial degeneration (e.g., nephrotic syndrome and essential hypertension); very poor ACh synthesis occurs when syncytial degeneration is advanced (e.g., preeclampsia, eclampsia, intra-uterine death of fetus, vesicles of hydatid mole and placental tissue infarcts); and ACh synthesis is nil in material that is completely devoid of syncytiotrophoblast (e.g., placental tissue-like material, which rarely appears in between the vesicles of hydatid moles). In essence, the degree of reduction in ACh synthesis seems to correlate with the state of the syncytiotrophoblast in various pathological conditions; and ACh synthesis is greatly reduced during syncytial degeneration. It is concluded that the capacity of the placenta to synthesize ACh reflects the state of the syncytiotrophoblast.