Respiratory and cardiovascular reflexes elicited by nasal instillation of capsaicin to anesthetized, spontaneously breathing dogs.

Cardiopulmonary reflexes elicited by capsaicin (CAPS) instilled into the nasal passages were determined in 6 anesthetized dogs breathing spontaneously. Nasal instillation of CAPS (10 microg/ml, 10 ml) induced: 1) apneic response characterized by an increase in expiration time; 2) bronchoconstrictor response characterized by an increase in lung resistance and a decrease in dynamic compliance; and 3) cardiovascular response characterized by a decrease in heart rate and an increase in arterial blood pressure. These reflex responses to CAPS were attenuated by pretreatment with a higher dose of CAPS (100 microg/ml, 10 ml), suggesting desensitization of CAPS-sensitive endings. These results suggest that marked cardiopulmonary reflexes are produced by nasal CAPS instillation, which may result, at least in part, from stimulation of nasal CAPS-sensitive sensory afferents.