Human placental cholinergic system: Occurrence, distribution and variation with gestational age of acetylcholine in human placenta

Abstract

Although acetylcholine (ACh)-like activity was demonstrated in human placental extracts by a number of investigators, substances responsible for this activity were not identified. We found by gas Chromatographic techniques that the major component of the ACh-like activity of the term placenta was ACh (112 ± 7 nmoles/g of wet tissue). These results were confirmed by the separation of ACh from other quaternary ammonium compounds by column chromalography using Amberlite CG-50 resin. The placenta could be stored at 4 for a number of days without significant loss of ACh. Freezing and thawing of the placenta destroyed ACh. This indicates that ACh is bound within membranes. There were high concentrations of ACh in all segments of the placenta. The ACh concentrations in the concentric segments next to the periphery and the umbilical cord were lower than ACh concentrations in other segments. The concentrations of ACh in floating villi and the basal plate, which included the anchoring villi, were about 322 and 210% respectively, of that of the chorionic plate. There was variation in ACh content with gestational age: the highest concentration was found at about 22 weeks (wk) of gestation (nmoles/g at 9–12 wk, 129; 13–16 wk, 342 ± 31; 17–20 wk, 317 ± 32; 21–24 wk, 723 ± 63; 25–28 wk, 231; 29–32 wk, 249; 33–36 wk, 153 ± 15; 37–40 wk, 105 ± 7; and 41–44 wk, 88 ± 5). These observations associate ACh with syncytiotrophoblast. Choline acetyltransferase (ChA) has a similar pattern of variation with gestational age. The placental cholinergic system (as indicated by ChA ACh) was fully formed at the early fetal period of histogenesis and functional maturation, during which the fetus exhibits the fastest rate of growth.