Human placental choline acetyltransferase activity at parturition.

Choline acetyltransferase (ChAT) activity measured in human placentae obtained during labour, or after labour of spontaneous onset, was significantly lower than that measured in placentae obtained before the onset of labour. The reduction in ChAT activity may partly account for the reduction in placental acetylcholine (ACh) content and release into maternal vessels at this time. When cycloheximide (10 micrograms/ml) was infused for 3 h into both fetal and maternal vessels of the perfused placental lobule, it did not significantly alter placental ChAT activity or ACh output from the fetal vessels, though it significantly reduced placental beta HCG release from the maternal side of the perfused lobule. These results suggest that regulation of placental ChAT activity at the time of human parturition may be due to endogenous modulators of its activity, rather than to acute changes in the synthesis of this enzyme.