Lung reflexes and nasal vascular resistance in the anaesthetized dog.

1. In pentobarbitone-anaesthetized dogs the nasal vasculature was perfused on both sides, and nasal vascular and airflow resistances were measured together with blood pressure, heart rate and tidal airflow. 2. Capsaicin was injected intravenously to stimulate lung C-fibre receptors, and veratrine to stimulate pulmonary stretch receptors and cardiac receptors. Injections with both drugs were repeated after pulmonary denervation and after cervical vagosympathectomy. 3. Intravenous capsaicin caused hypotension, bradycardia and rapid shallow breathing, together with a decrease in nasal vascular resistance and little change in nasal airways resistance. Denervation showed that these effects came from lung reflexes, presumably from C-fibre receptors. 4. Intravenous veratrine caused similar effects to capsaicin before denervations, presumably due to stimulation of slowly adapting pulmonary stretch receptors. Left atrial injections of veratrine caused hypotension, bradycardia and hyperpnoea, together with an increase in nasal vascular resistance and little change in nasal airways resistance. Thus cardiac receptors seem to increase nasal vascular resistance. 5. Injections of capsaicin and veratrine into the nasal circulation decreased nasal vascular resistance, with a stimulation of breathing and changes in blood pressure. Denervations indicated that these were a combination of local and reflex actions.