1. We studied the effects of an intraperitoneal (i.p.) administration of atropine on bronchomotor tone induced by carbachol aerosols in anaesthetized and ventilated guinea-pigs and on the sensitivity of cough reflex to capsaicin aerosols in awake guinea-pigs. 2. The intraperitoneal administration of atropine (10-8-10-6 M kg-1) reduced carbachol (8 mg ml-1; 1 min)-induced increases in pulmonary insufflation pressure and a complete inhibition was achieved at a dose of 10-6 M kg-1 in anaesthetized guinea-pigs. 3. In awake guinea pigs, capsaicin aerosols (10-5-10-3 M) caused dose-dependent increases in the number of coughs. Atropine (10-7-10-6 M kg-1 i.p.) shifted the dose-response curves to capsaicin to the right in a dose-dependent fashion. Carbachol aerosols, at the maximal concentration (2 mg ml-1) that did not cause bronchoconstriction, shifted them to the left compared with the control. 4. Atropine (10-6 M kg-1 i.p.) significantly increased the provocative concentration of capsaicin that caused five coughs (P < 0.01) and carbachol aerosols (2 mg ml-1) significantly decreased it (P < 0.01). 5. We conclude that cholinergically mediated airway tone regulates cough sensitivity in awake guinea pigs.
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