Comparison of autonomic responses in the trachea isolated from normal and albumin‐sensitive guinea‐pigs

1 Mechanical and electrical responses to stimulation of the parasympathetic and sympathetic nerves were compared in the trachea isolated from normal guinea-pigs and from guinea-pigs sensitized to albumin and exposed repeatedly to inhaled albumin (a model of bronchial asthma). 2 Sensitized trachealis exhibited mechanical hyper-responsiveness to vagal stimulation characterized by a shift to the left of the frequency-response relationship and a 71% increase in the maximum response. 3 Transmembrane potential was significantly less negative in sensitized trachealis cells. 4 The amplitude of the depolarization evoked by vagal stimulation (4 or more pulses) was significantly greater in sensitized tissues. Vagally-mediated depolarization was associated with the appearance of regenerative electrical activity (spikes) in sensitized but not in control tissues. 5 Spontaneous discharge of slow waves occurred in cells from both control and sensitized trachea but the proportion of spontaneously active cells was higher in sensitized tissues. Spontaneous depolarization, like nerve-mediated depolarization, gave rise to abortive spikes only in sensitized trachealis. 6 Inhibitory responses to stimulation of the sympathetic stellate ganglion, mediated by beta-adrenoceptors, were unaltered in sensitized trachealis. 7 Possible explanations for the hyper-responsiveness to vagal input in sensitized trachealis are discussed.