Characterization of muscarinic receptors on the isolated guinea pig ileum at pharmacologically low concentrations.

1. Several selective and non-selective muscarinic agonists (McN-A-343, RS-86, arecoline, oxotremorine-M, pilocarpine, cis-dioxolane, and acetylcholine) were examined for relaxant activity in the isolated guinea-pig ileum at pharmacologically low concentrations. 2. The concentrations studied include: 1 x 10(-12) M, 3 x 10(-12) M, 1 x 10(-11) M, 3 x 10(-11) M and 1 x 10(-10) M. 3. None of the compounds exhibited relaxant activity in both the field and non-field stimulated ileum. 4. All of the above compounds exert muscarinic agonist activity in a concentration range of 1 x 10(-9) M to 1 x 10(-6) M (Williams et al., 1992). 5. Thus, in the isolated guinea-pig ileum, muscarinic agonists do not exert relaxant activity of the gastrointestinal tract at low concentrations.