Acetylcholine. An acetic acid ester of the organic base choline, acetylcholine is one of the substances which mediates the transmission of nerve impulses from one nerve to another, or from a nerve to the organ it acts on such as muscles. It acts on both muscarinic receptors ( blocked by atropine and responsible for ganglionic and parasympathetic and also for sympathetic innervation of sweat glands) and nicotinic receptors (responsible for transmission of nerve impulses to muscles and blocked by curare, thus causing paralysis). Acetylcholine is rapidly destroyed by cholinesterase, an enzyme present in th blood. Anticholinergic drugs such as physostigmine prolong the action of acetylcholine.