Role of vagal lung C-fibres in the cardiorespiratory effects of capsaicin in monkeys.
Apnoea, bradycardia and hypotension were elicited by right atrial injections of capsaicin in anaesthetized monkeys. At the threshold dose (2.5 +/- 0.3 microgram/kg), tachypnoea was elicited (latency 1.6 +/- 0.2 s) which got replaced by apnoea with higher doses of capsaicin. These responses persisted (1) after cooling the cervical vagi to 6-8 degrees C, and (2) after instilling xylocaine into the pericardial sac. Tachypnoea and apnoea were elicited after bilateral cervical vagotomy also, but only with higher doses and after a longer latency (5.0 +/- 0.3 s). Right atrial injection of capsaicin and insufflation of halothane stimulated vagal pulmonary C-fibre receptors with a latency of 1.7 +/- 0.7 s and 0.2 +/- 0.1 s, respectively. Tachypnoea/apnoea, bradycardia and hypotension were elicited by left atrial injection of capsaicin also (threshold dose: 5.0 +/- 1.2 micrograms/kg). The respiratory responses persisted (1) after instilling xylocaine into the pericardial sac, and (2) after bilateral cervical vagotomy suggesting that they were due to stimulation of non-cardiac receptors with sympathetic afferents. It is concluded that the initial respiratory responses elicited by right atrial injection of capsaicin were due to stimulation of pulmonary C-fibre receptors with vagal afferents.
Ravi
K
K
Department of Physiology, V.P. Chest Institute, University of Delhi, India.
Singh
M
M
D000280:Administration, Inhalation; D000818:Animals; D002211:Capsaicin / Q000494:pharmacology*; D002319:Cardiovascular System / Q000187:drug effects; D003080:Cold Temperature; D005260:Female; D006221:Halothane / Q000494:pharmacology; D006321:Heart / Q000187:drug effects*; D006325:Heart Atria; D007267:Injections; D008012:Lidocaine / Q000494:pharmacology; D008168:Lung / Q000294:innervation*; D008253:Macaca mulatta; D008297:Male; D009412:Nerve Fibers / Q000502:physiology*; D010496:Pericardium; D012137:Respiratory System / Q000187:drug effects*; D014628:Vagotomy; D014630:Vagus Nerve / Q000502:physiology*
D008012:Lidocaine; D002211:Capsaicin; D006221:Halothane