Cholinergic influence on the sensitivity of cough reflex in awake guinea-pigs

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.