Abstract
The actions of both reversible and irreversible anticholinesterase drugs on the nerve-free smooth muscle of the chick amnion are described. The tertiary compound physostigmine and the irreversible inhibitor diisopropylfluorophosphonate were found to be active in causing contractions, whereas the quaternary compound neostigmine and the irreversible inhibitor Mipafox were only slightly active in this respect. Manometric studies showed that all four compounds were highly active, however, in inhibiting the cholinesterase found in the chick amnion. The effects produced by these compounds in the organ bath are thought to be due to the accumulation of endogenously produced acetylcholine within the tissue. Evidence for an intracellular action of endogenously produced acetylcholine in the smooth muscle of the chick amnion is discussed.