Degradation of acetylcholine in human airways: role of butyrylcholinesterase

1 Neostigmine and BW284C51 induced concentration‐dependent contractions in human isolated bronchial preparations whereas tetraisopropylpyrophosphoramide (iso‐OMPA) was inactive on airway resting tone. 2 Neostigmine (0.1 μm) or iso‐OMPA (100 μm) increased acetylcholine sensitivity in human isolated bronchial preparations but did not alter methacholine or carbachol concentration‐effect curves. 3 In the presence of iso‐OMPA (10 μm) the bronchial rings were more sensitive to neostigmine. The pD2 values were, control: 6.05 ± 0.15 and treated: 6.91 ± 0.14. 4 Neostigmine or iso‐OMPA retarded the degradation of acetylcholine when this substrate was exogenously added to human isolated airways. A marked reduction of acetylcholine degradation was observed in the presence of both inhibitors. Exogenous butyrylcholine degradation was prevented by iso‐OMPA (10 μm) but not by neostigmine (0.1 μm). 5 These results suggest the presence of butyrylcholinesterase activity in human bronchial muscle and this enzyme may co‐regulate the degradation of acetylcholine in this tissue.