ROLE OF PULMONARY C-FIBERS IN ADENOSINE-INDUCED RESPIRATORY INHIBITION IN ANESTHETIZED RATS

The clinical use of adenosine is commonly associated with pulmonary si de effects, namely dyspnea, that suggest the possible involvement of b ronchopulmonary sensory afferents. Our objective in this study was to characterize the effects of adenosine on breathing and to determine wh ether the vagal pulmonary afferents play a role in mediating these eff ects. We measured respiratory and cardiovascular changes in anesthetiz ed, spontaneously breathing rats after bolus injections of adenosine a t therapeutic doses. Right atrial injection of adenosine (0.04-0.6 mg/ kg) elicits, in a dose-dependent manner, a pulmonary chemoreflex-like response consisting of a delayed apnea, bradycardia, and hypotension. In contrast, the classic capsaicin-elicited pulmonary chemoreflex occu rs immediately after injection. Perineural capsaicin treatment of the cervical vagi blocked the adenosine-induced respiratory inhibition. Le ft ventricular administration of adenosine failed to elicit an apneic response. Pretreatment with the adenosine Al-receptor antagonist 8-cyc lopentyl-1,3-dipropylxanthine attenuated the adenosine-induced apnea. These results indicate that adenosine elicits a respiratory inhibition via stimulation of pulmonary C fibers and that activation of the A(1) -receptor is probably involved. It is unclear, however, what accounts for the exceedingly long latency in this response.