Reflex modulation of carotid sinus baroreceptor activity in the dog.

Carotid sinus baroreceptor (CBR) sensitivity may be increased by electrical stimulation of sympathetic nerves passing to the carotid sinus region. It remains unknown if reflexly induced changes in efferent sympathetic discharge affect CBR function. In 17 anesthetized dogs, we reflexly induced alterations in sympathetic discharge and recorded CBR activity originating from a vascularly isolated carotid sinus. The stimulus to the baroreceptors was pulsatile with constant mean and pulse pressure. Occlusion of the contralateral common carotid artery (n = 6) resulted in a reflex increase in arterial pressure (116 +/- 10 to 153 +/- 14 mmHg) and an increase (121 +/- 2% of control) in baroreceptor activity (P less than 0.05). Inferior vena caval occlusion (n = 6), which induced a reduction in arterial pressure (145 +/- 19 to 75 +/- 21 mmHg), also provoked an increase (141 +/- 10% of control) in baroreceptor discharge (P less than 0.05). Raising pressure (to 200 mmHg) in the contralateral carotid sinus (n = 7) resulted in a reflex decrease in arterial pressure (169 +/- 16 to 129 +/- 13 mmHg) and a reduction (82 +/- 3% of control) in baroreceptor activity (P less than 0.05). The changes in baroreceptor discharge were abolished by ipsilateral cervical sympathectomy or ganglionic blockade (n = 4). Our findings demonstrate that reflexly induced alterations in the activity of sympathetic fibers innervating the carotid sinuses can modulate baroreceptor discharge.