CARBACHOL IS A CHOLINE ESTER, IS A QUATERNARY AMMONIUM PARA-SYMPATHOMIMETIC WITH THE MUSCARINIC AND NICOTINIC ACTIONS OF ACETYLCHOLINE. CARBACHOL RELEASED FROM POSTGANGLIONIC PARASYMPATHETIC NERVES AND ALSO FROM SOME POSTGANGLIONIC SYMPATHETIC NERVES TO PRODUCE PERIPHERAL ACTIONS WHICH CORRESPOND TO THOSE OF MUSCARINE. IT IS NOT INACTIVATED BY CHOLINESTERASES SO THAT ITS ACTION ARE MORE PROLONGED THAN THOSE OF ACETYLCHOLINE.