The affinity of the antagonist dicyclomine for subtypes of muscarinic receptors has been assessed in the myenteric plexus-longitudinal muscle preparation of the guinea-pig. 2. Dicyclomine had a high affinity (pA2 9.13) for the neuronal M1-receptor whose activation by pilocarpine causes an increase in acetylcholine release. Dicyclomine had a low affinity for both the prejunctional M2-receptor (pA2 7.61) mediating inhibition of the electrically-evoked acetylcholine release and the postjunctional M2-receptor (pA2 7.21). 3. It is concluded that dicyclomine distinguishes between M1- and M2-muscarinic receptors in functional experiments.
