Journal of Applied Physiology, Vol 75, Issue 5 2173-2179, Copyright © 1993 by American Physiological Society
Reflex control of the tracheal vasculature of sheep
S. E. Webber and J. G. Widdicombe
Department of Physiology, St. George's Hospital Medical School, London, United Kingdom.
Arteries to the cervical trachea were perfused at constant flow in
anesthetized sheep. Perfusion pressures (PP), blood pressure (BP), and
changes in tracheal smooth muscle tone (Ptr) were measured. Stimulation of
pulmonary C-fiber receptors decreased PP (-6.5%) and BP (-16.8%) and
increased Ptr (+61.5%), changes prevented by vagotomy and therefore reflex.
Stimulation of cardiac receptors and slowly adapting pulmonary stretch
receptors decreased PP (-7.9%) and BP (-21.0) and increased Ptr (+19.0%),
changes reversed by vagotomy and therefore reflex. Stimulation and
inhibition of slowly adapting pulmonary stretch receptors had no
vagal-dependent effect on PP and BP, but inflation decreased (-20.3%) and
deflation increased Ptr (+35.2%), effects abolished by vagotomy and
therefore reflex. Systemic hypoxia increased PP and BP before and after
vagotomy (+12.2 and +40.3%), effects greatly reduced by cutting the carotid
body nerves; it increased Ptr (+29.8%), an effect abolished by vagotomy and
cutting the carotid body nerves. Systemic hypercapnia increased PP
(+16.9%), BP (+20.5%), and Ptr (+36.2%), the first two responses being
unaffected by vagotomy and the last almost abolished. Stimulation of
carotid body chemoreceptors by KCN increased PP (+22.5%), BP (+104.7%), and
Ptr (+8.5%), all responses prevented by cutting the carotid body nerves.
Responses to intravenous injections of KCN were similar.
