Acute resetting of carotid sinus baroreceptors. I. Dissociation between discharge and wall changes

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Abstract
The purpose of this study was to assess whether mechanical changes in the carotid sinus wall could account for acute resetting of the carotid sinus baroreceptors in chloralose-anesthetized dogs. Threshold pressure and pressure-discharge curves for single-unit baroreceptors were determined before and after the vascularly isolated carotid sinus was exposed to brief increases or decreases in base-line pressure. When intrasinus pressure was increased by 30 mmHg for 15 min, threshold pressure increased by 9 +/- 1.3 (SE) mmHg (n = 12), and when intrasinus pressure was decreased by 30 mmHg threshold pressure decreased by 14 +/- 4.2 mmHg (n = 9), with no change in gain of the pressure-discharge curves. In 14 experiments carotid sinus pressure was increased from 70 (control) to 160 mmHg for only 5 min (reset) and returned to 70 mmHg for 10 min (recovery). After exposure to the higher pressure, threshold pressure increased from 75 +/- 3.8 to 94 +/- 4.4 mmHg, and carotid sinus diameter (sonomicrometer) and calculated wall strain at each pressure increased. After the recovery period, baroreceptor threshold pressure returned to 75 +/- 4.1 mmHg, but diameter and wall strain remained elevated. We interpret our finding that baroreceptor resetting and recovery are not accompanied by reciprocal changes in carotid sinus diameter to indicate that a mechanical mechanism alone cannot explain acute resetting.