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

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.