Early depression of the baroreceptor sensitivity during onset of hypertension

Abstract

We studied the correlation of changes in gain sensitivity of the baroreceptors and the development of resetting of the baroreceptors 2 and 6 days after the onset of hypertension produced by siibdiaphragmatic aortic constriction in rats. Mean arterial pressure of anesthetized rats was maintained at approximately the same level as that of conscious rats, and baroreceptor function curves were studied on a beat-to-beat basis by computer. After 2 days of hypertension, the difference between the systolic pressure threshold and the control diastolic pressure was 13±2 mm Hg (125±3 versus 138±4 mm Hg). Individual values showed that in seven of nine hypertensive rats, the difference was less than 15 mm Hg, indicating complete resetting. After 6 days of hypertension, all rats exhibited complete resetting, when the systolic pressure threshold was similar to control diastolic pressure (143±4 versus 141±2 mm Hg), indicating, tnat more than 2 days of hypertension is necessary for full displacement of the pressure thresholds when all hypertensive rats are considered. Slopes of the baroreceptor curves after 2 and 6 days of hypertension showed that baroreceptor gain was depressed by 25% and 34%, respectively. The difference was not statistically significant (1.07±0.054% versus 0.94±0.049% and 1.43±0.075% in controls). When changes in pressure were circumscribed to a more physiological range, a depression of 25% in response to +10 mm Hg and 37% in response to −10 mm Hg was observed. The data indicate that a depression of the baroreceptor gain, similar toAthat observed previously after 2 months of hypertension, is already present after only 2–6 days of hypertension, when complete resetting is also detected. © 1992 American Heart Association, Inc.