Multireceptor activation of the pulmonary chemoreflex

Area of Science:

• Physiology
• Respiratory System
• Neuroscience

Background:

• Pulmonary C-fibers are known to initiate apnea and changes in breathing after capsaicin injection.
• The role of secondary stimulation of pulmonary stretch receptors via reflex bronchoconstriction in this response remains unclear.

Purpose of the Study:

• To determine the contribution of secondary stimulation of slowly adapting pulmonary stretch receptors to the breathing pattern changes induced by the pulmonary chemoreflex.
• To investigate the influence of muscarinic receptor blockade on the pulmonary chemoreflex.

Main Methods:

• The pulmonary chemoreflex was evoked in spontaneously breathing dogs using right atrial injections of capsaicin.
• Muscarinic receptors were blocked using atropine before capsaicin administration.
• Breathing pattern, arterial blood pressure, and heart rate were monitored.

Main Results:

• Capsaicin injection induced apnea, hypotension, bradycardia, rapid shallow breathing, and bronchoconstriction before atropine administration.
• After atropine blockade, bronchoconstriction was abolished, but other components of the pulmonary chemoreflex (apnea, hypotension, bradycardia, rapid shallow breathing) remained.
• The magnitude of change in all components except apnea was significantly attenuated after atropine treatment.

Conclusions:

• The classic pulmonary chemoreflex is a complex phenomenon primarily initiated by pulmonary C-fiber stimulation.
• Secondary stimulation of slowly adapting pulmonary stretch receptors, particularly via capsaicin-induced bronchoconstriction, significantly influences the overall pulmonary chemoreflex response.
• Muscarinic receptor blockade with atropine attenuates the pulmonary chemoreflex, highlighting the role of bronchoconstriction in modulating the response.