Baroreceptor reflex cardiovascular control in mongrel dogs and racing greyhounds

The open-loop carotid sinus baroreflex control of arterial pressure-flow relations were compared in mongrel dogs and racing greyhounds (GH) anesthetized with alpha-chloralose. The carotid sinuses were bilaterally isolated and perfused under controlled pressure. Pulsatile pressure and flow were simultaneously measured in the ascending aorta, the celiac, superior mesenteric, left renal, and right iliac arteries. Open-loop set point values of mean arterial pressure were higher in GH before and after vagotomy. Reflex gains were similar before vagotomy but lower in GH after vagotomy. The overall range of control of arterial pressure was the same before vagotomy but smaller in GH after vagotomy. The variation of mean arterial pressure with mean carotid sinus pressure in GH was shifted toward higher pressure levels similar to resetting. The overall effects of vagotomy on carotid sinus baroreceptor reflex responses were smaller in GH. Operating point values of regional resistance were generally smaller in GH. Operating point sensitivities of regional resistance were the same except for the iliac bed, which was more sensitive in GH. These results document significant regional differences in the baroreceptor control of regional hemodynamics between mongrels and greyhounds that could contribute to altered responses especially to "hypertensive" perturbations.