Airway receptors in cough.

Sulphur dioxide inhalation (200 ppm) suppresses the inflation apnea in rabbits, but not in dogs. In rabbits, SO2 blocks airway slowly adapting stretch receptors (SAR) while rapidly adapting irritant receptors (RAR) remain largely unaffected. We studied cough elicited by mechanical irritation of the extrapulmonary airways and larynx in 13 rabbits and 4 dogs, anesthetized and spontaneously breathing, before and after SO2 inhalation. In rabbits, once SO2 had blocked the Hering-Breuer inflation reflex, mechanical stimulation of the trachea and carina failed to elicit cough; laryngeal stimulation was still effective though the response was attenuated. In dogs, SO2 inhalation (even up to 1,000 ppm) did not abolish either inflation apnea or cough to tracheobronchial mechanical stimulation. We recorded the response to mechanical probing of tracheal RAR, before and after SO2 exposure, in 6 rabbits. We found that the activity of these RAR was still present after cough and inflation apnea had disappeared. These results suggest a significant role of slowly adapting airway receptors in the cough reflex.