Methacholine is used only for bronchial hyperreactivity diagnostics. A synonym of
this drug is provocholine.
Acetyl-β-methylcholine bromide (methylcholine bromide, methacholine bromide, Mch), a muscarinic acetylcholine receptor agonist, may be used in studies that involve the indentification, characterization and mechanism of action of muscarinic acetylcholine receptors. Mch may be used as a reference material in procedures used to detect or quantify its presence.
Methacholine can exist as (S) and (R) enantiomers.Although the chemical is used as the racemic mixture, itsmuscarinic activity resides principally in the (S)-isomer.The (S)/(R) ratio of muscarinic potency for these enantiomersis 240:1.
A minor structural change is the presence of a methyl group at the β-carbon atom of
choline, which results in two main changes in the pharmacological profile of the molecule.
Unlike acetylcholine, methacholine is hydrolyzed only by acetylcholinesterase, and the
rate of hydrolysis is significantly less than with acetylcholine. Thus, the action of methacholine is significantly longer lasting than acetylcholine. Moreover, the presence of a
methyl group at the β-carbon of choline provides the compound with a greater selectivity
of action. Methacholine directly acts on muscarinic receptors of smooth muscle, glands,and the heart, and it has a very weak effect on nicotinic receptors of the autonomic ganglions of skeletal muscle.
Methacholine, 1-acetoxy-2-(N,N,N-trimethyl)propyl ammonium chloride
(13.1.4) or acetyl-β-methylcholine can be synthesized by any of the methods described
above [8]
