Rapid resetting of the carotid baroreceptor reflex in the cat

The carotid baroreceptor depressor reflex of the chloralose-anesthetized cat was examined to determine the role of the prevailing carotid pressure in determining the threshold, gain, and range of operation of the reflex response. After the pressure of an isolated perfused carotid sinus was held at 80 mmHg for 20 min the threshold pressure necessary to elicit the reflex systemic blood pressure response was 78 +/- 2.9 (SE) mmHg (n = 5). When carotid pressure was maintained for 20 min at 120 and 160 mmHg the threshold rose to 113 +/- 2.9 and 126 +/- 3.0 mmHg, respectively. The resetting of the threshold to a stable value upon elevating or reducing carotid sinus pressure was accomplished within 15--20 min. The entire range of operation of the reflex response was shifted to higher carotid pressures as the holding pressure was elevated. The midrange gain of the response was unchanged at the three holding pressures tested. These findings indicate that the carotid baroreceptor reflex need not operate over a fixed range but that the range may be rapidly adjustable to the prevailing pressure. When arterial pressure is sustained at a level that is elevated or depressed from normal the carotid baroreceptor reflex acutely resets to operate in the range of the prevailing pressure with a threshold that has moved toward the prevailing pressure.