ABSTRACT
The muscarinic receptor antagonists interact with the muscarinic receptors, produce no stimulant or agonist effects by themselves, but inhibit the effects of endogenously released Ach or exogenously introduced muscarinic agonists. The principal targets for antagonism are the postjunctional M2 and M3 muscarinic receptors on cardiac and smooth muscle and glandular tissues, which are normally activated by the release of Ach from postganglionic parasympathetic nerve terminals. Muscarinic receptors are distributed throughout the brain and, provided that the antagonist is capable of crossing the blood-brain barrier, the central effects upon mood, behaviour and cognitive powers with therapeutic doses are primarily due to antagonism of muscarinic receptors. The competitive tertiary amine class of muscarinic antagonists has been combined with the ß-haloalkylamine structure to produce irreversible muscarinic antagonists. The prototype antimuscarinic agent is atropine and a description of its pharmacology serves to illustrate the pharmacological effects of muscarinic blockade in general and remains relevant to the majority of therapeutically useful agents.
