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Reflex bronchoconstriction induced by capsaicin in the dog
Summary
Capsaicin injection into pulmonary circulation triggers reflex bronchoconstriction in dogs. This vagal reflex may aid fluid movement from lung microvasculature to the peribronchial space.
Area of Science:
- Pulmonary Physiology
- Respiratory Reflexes
- Neurogenic Inflammation
Background:
- The role of pulmonary receptors in regulating airway caliber is not fully understood.
- Capsaicin is a known stimulant of sensory nerves, including those in the lungs.
Purpose of the Study:
- To investigate if stimulation of pulmonary receptors by capsaicin causes reflex changes in airway size.
- To elucidate the neural pathways involved in this reflex.
Main Methods:
- Anesthetized, mechanically ventilated dogs were used.
- Airway diameters were measured using roentgenography after tantalum dust outlining.
- Capsaicin was injected into the right and left ventricles, and effects on airway diameter, heart rate, and pressures were recorded.
- Vagotomy was performed to assess the role of the vagus nerve.
Main Results:
- Right ventricular capsaicin injection caused significant bronchoconstriction (20% decrease in airway diameter), reduced heart rate, and lowered aortic and pulmonary artery pressures.
- Left ventricular capsaicin injection had less pronounced effects, not altering airway diameter.
- Vagotomy abolished the capsaicin-induced changes in airway diameter and heart rate.
Conclusions:
- Pulmonary receptors sensitive to capsaicin can induce reflex bronchoconstriction via the vagus nerve.
- This vagal reflex may play a role in regulating fluid balance in the lung by reducing peribronchial pressure.