Submitted on November 14, 2002
Accepted on January 6, 2003
Afferent vagal pathways mediating respiratory reflexes evoked by reactive oxygen species in the lungs of anesthetized rats
Ting Ruan1, Ching-Yin Ho2, and Yu Ru Kou1*
1 Institute of Physiology, School of Medicine, National Yang-Ming University, Taipei, Taiwan
2 Department of Otolaryngology, Taipei Veterans General Hospital, Taipei, Taiwan
* To whom correspondence should be addressed. E-mail: yrkou{at}ym.edu.tw.
We investigated the afferent vagal pathways mediating respiratory reflexes evoked by reactive oxygen species in the lungs of anesthetized rats. Spontaneous inhalation of 0.2% aerosolized H2O2 acutely evoked initial bradypnea followed by delayed tachypnea which was frequently mixed with delayed augmented inspiration. The initial response was abolished after perivagal capsaicin treatment (PCT), but was prolonged during vagal cooling to 7 °C (VC); PCT and VC are known to differentially block the conduction of unmyelinated C and myelinated fibers, respectively. The delayed responses were eliminated during VC, but emerged earlier after PCT. A vagotomy, catalase (an antioxidant for H2O2), dimethylthiourea (an antioxidant for .OH), or deferoxamine (an antioxidant for .OH) largely or totally suppressed these reflexive responses, while sham nerve treatment, heat-inactivated catalase, saline vehicle, or iron-saturated deferoxamine failed to do so. These results suggest that 1) the H2O2-evoked initial and delayed airway reflexes are antagonistic and may result from stimulation of lung C fibers and rapidly adapting receptors, respectively; and 2) the reflex effects of H2O2 are in part due to the action of .OH on these afferents.
