Muscarinic receptor agonists and antagonists

Although four different subtypes of the muscarinic acetylcholine (ACh) rece ptor with functional correlates are known to exist (function for M5 is stil l unclear), all muscarinic agonists and antagonists in clinical practice on ly show very weak selectivity. Therefore, intensive investigations are in p rogress to develop subtype selective ligands. This review describes the fir st M1 agonists and antagonists of the presynaptic M2 receptor, which can be used in the treatment of Alzheimer's disease (AD), and M3 antagonists, whi ch will be useful in the treatment of urinary urge incontinence. In additio n, muscarinic agonists were found to exhibit analgesic effects and M4 antag onists may be useful in the treatment of movement disorders. However, the l atter two pharmacological findings will need more research work to become e stablished in clinical trials.