Reflexes from isolated carotid sinuses of intact and vagotomized conscious dogs.

Exposure of the vascularly isolated carotid sinuses of 8 conscious dogs to static pressures between 50 and 240 mmHg caused significantly smaller increases [23 +/- 5(SE) mmHg] than decreases (37 +/- 4 mmHg) in arterial pressure frossure and heart rate and shifted the stimulus-response curve upward. Bilateral cervical vagotomy in conscious dogs caused sustained (3 h) increases in arterial pressure (40 +/- 5 mmHg), significantly larger than after atropinization (7 +/- 2 mmHg). In anesthetized, but not in conscious dogs, high sinus pressure reversed the hypertension caused by vagotomy. After vagotomy, low sinus pressure resulted in arterial pressures greater than 200 -mHg. In conscious dogs the carotid baroreflex can widely vary arterial pressure and heart rate despite buffering by extracarotid baroreceptors with vagal afferents, but cannot fully compensate for the acute loss of the latter. Extracarotid baroreceptors actively participate with carotid baroreceptors in the regulation of arterial pressure and better buffer carotid baroreflex-induced increases than decreases in arterial pressure.