Study of the nicotinic activity of very potent muscarinic agents

The nicotinic activity of seven cholinergic agents endowed with a very high muscarinic activity (carbachol, methylfurtrethonium, cis-2-methyl-4-trimethylammoniummethyl-1,3-dioxolane, cis-2-methyl-5-trimethylammoniummethil-1,3-oxathiolane, muscarine, muscarone, oxotremorine) has been studied on the frog rectus abdominis. Carbachol is the most active compound with an EC50 value of 1.98 X 10(-6) M; the ratio between nicotinic and muscarinc activity is 67. Methylfurtrethonium and oxotremorine are the least potent and also behave as "partial agonists". Muscarine is devoid of activity. It is concluded that the nicotinic component does not interfere with the evaluation of the muscarinic potency of the compounds under investigation.