ABSTRACT
Atropine and its allied drugs (hyoscyamine, scopolamine, homatropine, etc.) are autonomic blocking agents that inhibit the action of the postganglionic cholinergic nerves and were, therefore, formerly designated as depressants of the parasympathetic system, or as antiparasympathomimetic agents. These drugs differ from nicotine and curare, which are also depressants of the parasympathetic system but which act as blocking agents on preganglionic cholinergic nerves. Atropine in therapeutic doses has no effect on the nicotinic actions of acetylcholine but specifically blocks all muscarinic responses of injected acetylcholine, whether excitatory as in the intestine, or inhibitory as in the heart. It fails, however, to block all cholinergic nerve stimulations and also exerts effects that are not explicable on the basis of its antagonism to acetylcholine. In addition to their action in blocking the muscarinic effects of acetylcholine, atropine and its allies exert important effects on the central nervous system (see also Figures 12 and 26).
