Chronic localized hypotension and resetting of carotid sinus baroreceptors. Electrophysiological and histological studies in the dog.

Resetting of carotid sinus (CS) baroreceptors to chronically elevated systemic pressure in hypertension has been demonstrated. The effects of chronic system hypotension on CS baroreceptor afferents has not been elucidated, however. The purpose of the present study was to determine the electrophysiological and histological characteristics of CS baroreceptors exposed to chronic hypotension. Chronic unilateral hypotension was produced by anastomosis of the common carotid artery to the external jugular vein. CS nerve activity and histology of the normotensive sinus (mean CS pressure +/- SD = 96 +/- 10.9 torr) were compared to those of the hypotensive sinus (mean CF pressure 50 +/- 14.2 torr) 44-49 days after anastomosis in nine mongrel dogs. An isolated CS pouch preparation was used to produce standard pressure changes. Threshold pressure for hypotensive sinuses (15.5 +/- 5.19 torr) was significantly less (P less than 0.05) than for normotensive sinuses (40.6 +/- 9.73 torr). Saturation pressure was also significantly less in the hypotensive sinus (P less than 0.05). There were no significant differences between slopes of the stimulus-response curve or in architecture of intima or media of the two sides. Thus, the stimulus-response curve was shifted to the left in chronic CS hypotension, and this effect could not be related to a change in CS light microscopic histology.