Capsaicin-induced bronchial vasodilation in dogs: central and peripheral neural mechanisms.
In 21 anesthetized dogs, we placed a flow probe around the right bronchial artery and examined changes in bronchial blood flow and bronchial vascular conductance when pulmonary C-fibers were stimulated by right atrial injection of capsaicin. When vagus nerves were intact, capsaicin evoked a pulmonary depressor chemoreflex and increased bronchial blood flow by 125% and bronchial vascular conductance by 175%; flow in an adjacent intercostal artery did not increase. Injection of color-coded microspheres revealed that blood flow to mucosa of lower trachea and to a peripheral bronchus doubled, whereas flow to posterior tracheal wall increased little. Cooling (to -1 degree C) or cutting cervical vagi (in 17 dogs) abolished the pulmonary chemoreflex and abolished all bronchial vascular effects in nine dogs but 33% of the vasodilation persisted in eight. In five of six dogs, this persisting vasodilation was potentiated by phosphoramidon (a neutral endopeptidase inhibitor that retards breakdown of neuropeptides released by C-fibers). Atropine reduced the capsaicin-induced bronchial vasodilation by approximately 30%. We conclude that the bronchial vasodilation was largely due to a centrally mediated vagal reflex and that a neuropeptide-dependent axon-reflex component was also present in about one-half the dogs.
Pisarri
T E
TE
Cardiovascular Research Institute, University of California, San Francisco 94143-0130.
Coleridge
J C
JC
Coleridge
H M
HM
D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001285:Atropine / Q000494:pharmacology; D001794:Blood Pressure / Q000187:drug effects; D001980:Bronchi / Q000098:blood supply*; D002211:Capsaicin / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D002302:Cardiac Output / Q000187:drug effects; D002490:Central Nervous System / Q000187:drug effects*; D004285:Dogs; D006020:Glycopeptides / Q000494:pharmacology; D006339:Heart Rate / Q000187:drug effects; D008863:Microspheres; D009092:Mucous Membrane / Q000098:blood supply / Q000187:drug effects; D009431:Neural Conduction / Q000187:drug effects; D010525:Peripheral Nerves / Q000187:drug effects*; D012018:Reflex / Q000187:drug effects; D012039:Regional Blood Flow / Q000187:drug effects; D014628:Vagotomy; D014664:Vasodilation / Q000187:drug effects*
D000900:Anti-Bacterial Agents; D006020:Glycopeptides; D001285:Atropine; D002211:Capsaicin; C008890:phosphoramidon