Localization of irritant receptors in the airways of the dog.

In dogs the authors have recorded from single fibres of the vagus nerve the action potentials originating from rapidly adapting receptors (irritant receptors) of the tracheo-bronchial tree activated both by inflation and deflation and by i.v. injection of histamine. A gross localization between extrapulmonary airways was established for 196 such receptors by probing the structures containing them. For 82 receptors a precise localization was determined within the extrapulmonary airways and for 51 receptors, localized in the lung parenchyma, a further precise localization was established along the intrapulmonary airways be dissecting the lung tissue. 66.9% of these receptors were found to be in the intrapulmonary airways and 33.1% in the extrapulmonary airways. Their distribution along the tracheo-bronchial tree resulted as follows: 4.75% in the higher 2/3 of the trachea, 9.25% in the lower 1/3 of the trachea and the carina, 19.0% in the main bronchus, 25.0% in the lobar bronchi, 36.8% in bronchi having a diameter larger than 1 mm and 5.2% in bronchi having a diameter smaller than 1 mm. Therefore the concentration of irritant receptors increases going from the upper trachea to the lobar bronchi and then sharply decreases reaching the smaller airways.