Characterization of antimuscarinic effect of cimetropium bromide in guinea pig ileum

Pharmacological characteristics of cimetropium bromide (cimetropium), a muscarinic receptor antagonist, were studied in longitudinal muscle preparations with myenteric plexus of guinea-pig ileum. Cimetropium was shown to have more potent antimuscarinic effect than butylscopolamine in inhibition of contraction of the preparations. Interestingly, when the inhibitory effects of cimetropium were compared in respect of relative potency to atropine between its effects on electrical field stimulation or nicotine-, and exogenous ACh-induced contraction, it has a more potent effect on the former contraction than that on the latter one. In the superfusion experiments of the preparation which had been preloaded with labelled choline, cimetropium decreased the labelled ACh release induced by electrical field stimulation under the muscarinic autoinhibition blocked-condition. From these findings, two pharmacologically characteristic effects of cimetropium in addition to post-synaptic muscarinic receptor antagonism were suggested: one is a weak effect on muscarinic autoreceptors in comparison to atropine and the Other is an inhibitory effect on the ACh release.