Extent of rapid baroreceptor resetting during first hours of hypertension.

Rapid or acute resetting of the aortic baroreceptors was studied in anesthetized rats during the onset and maintenance of hypertension produced by subdiaphragmatic aortic constriction for up to 6 h. After 2 min of hypertension, the systolic threshold pressure for activation of the baroreceptors increased by 33% of the total 27-mmHg increase of the control diastolic pressure. Maximal resetting of 46 and 52% was demonstrable after 20 and 30 min of hypertension. The shifts in pressure threshold were accompanied by parallel shifts in the entire baroreceptor function curves. After 30 min of hypertension, resetting was only partially (60%) reversed within the 30 min of pressure normalization. Resetting did not progress with time. Six hours after aortic constriction, resetting was only 38% (vs. 32% after 30 min). The data indicate that acute or rapid resetting of the aortic baroreceptors reaches a maximum within 20-30 min (40-50%) and remains stable for up to 6 h, with no apparent change in the baroreceptor gain.