Effects of drugs on the uptake of acetylcholine by human term placenta fragments.

An active concentrative component of the ACh accumulation in fragments of human term placenta followed kinetics predicted by the Michaelis-Menten equation (Km greater than 15 mM). This process was competitively inhibited by choline or hemicholinium-3, suggesting the possibility that a common carrier existed. Morphine reduced the 3 H-ACh uptake competitively. Imipramine, desmethylimipramine, haloperidol and chlorpromazine decreased the concentration ratios. This effect was uncompetitive with respect to chlorpromazine. Compared to drug actions on the ACh uptake in innervated tissue drug effects in the placenta were much less predictable for various classes of compounds.