REFLEX CONTROL OF THE TRACHEAL VASCULATURE OF SHEEP

Arteries to the cervical trachea were perfused at constant flow in ane sthetized sheep. Perfusion pressures (PP), blood pressure (BP), and ch anges in tracheal smooth muscle tone (Ptr) were measured. Stimulation of pulmonary C-fiber receptors decreased PP (-6.5%) and BP (-16.8%) an d 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 P tr (+19.0%), changes reversed by vagotomy and therefore reflex. Stimul ation and inhibition of slowly adapting pulmonary stretch receptors ha d no vagal-dependent effect on PP and BP, but inflation decreased (-20 .3%) and deflation increased Ptr (+35.2%), effects abolished by vagoto my and therefore reflex. Systemic hypoxia increased PP and BP before a nd after vagotomy (+12.2 and +40.3%), effects.greatly reduced by cutti ng the carotid body nerves; it increased Ptr (+29.8%), an effect aboli shed by vagotomy and cutting the carotid body nerves. Systemic hyperca pnia increased PP (+16.9%), BP (+20.5%), and Ptr (+36.2%), the first t wo responses being unaffected by vagotomy and the last almost abolishe d. Stimulation of carotid body chemoreceptors by KCN increased PP (+22 .5%), BP (+104.7%), and Ptr (+8.5%), all responses prevented by cuttin g the carotid body nerves. Responses to intravenous injections of KCN were similar.