Effects of the parasympathomimetic drug methacholine and its antagonist atropine on mucociliary activity

The effect on the mucociliary (m.c.) activity of the parasympathomimetic drug methacholine and its antagonist atropine was studied with the aid of a newly developed animal test model, designed for evaluating the effect of pharmacological substances on the m.c. wave frequency. Methacholine i.a. (0.01-2 micrograms/kg) was found to give a dose-dependent acceleration of the m.c. wave frequency, and the threshold dose 0.03 +/- 0.02 (+/- S.D.) micrograms/kg is suggested to be within physiological limits. The anticholinergic drug atropine i.a. (0.05-0.5 mg/kg) did not influence the basal m.c. wave frequency, but a dose of 0.2 mg/kg reduced or abolished the responses to methacholine (0.05-2 micrograms/kg). These results indicate that the basal m.c. activity functions independently of parasympathetic activity in anesthetized animals, that parasympathomimetic drugs influence the m.c. activity and that the effects of these drugs can be reduced or blocked by atropine.