| [ Summary ] |
Muscarinic receptor antagonists block the action of acetylcholine against muscarinic receptors which exist in the viscera, controlled by parasympathetic nerves, the central nervous system and ganglions. Clinically, they are seen to be drugs which produce parasympatholytic actions. In the area of the digestive tract they are used for diseases or pathologic states related to hypersecretion a/o hyperanakinesis due to hyperfunction of parasympathetic nerves, such as abdominal pain induced by spasm of the smooth muscles of the gastrointestinal tract, peptic ulcer, irritable bowel syndrome, etc. However, we must beware of overdosage because they display several adverse effects by acting against other muscarinic receptors, e.g. visual disturbances, an increase of intraocular pressure, thirst, palpitations, tachycardia, or dysuria. They were first used for treatment peptic ulcers with the expectation of acid-inhibitory action, but this action cannot be displayed well because of the dose-limitations in order to reduce adverse effects. Recently pirenzepine, which was developed as a drug to selectively antagonize the muscarinic receptors of the central nervous system and ganglions, has been used in place of the usual muscarinic receptor antagonists because it has been shown to display a relatively high affinity for parietal cells with a low affinity for smooth muscles and the heart. |