Rapid baroreceptor resetting in chronic hypertension. Implications for normalization of arterial pressure.

Abstract

The purpose of this study was to examine the ability of baroreceptors of renal hypertensive rabbits to reset rapidly during acute changes in arterial pressure. The carotid sinus (CS) was vascularly isolated and baroreceptor activity was recorded during slow ramp increases in CS pressure in hypertensive (one-kidney, one wrap; 127±3 mm Hg) and normotensive (one-kidney, no wrap; 85 ±3 mm Hg) rabbits anesthetized with chloralose. Control measurements were made after holding pressure for 10-15 minutes at the level of arterial pressure recorded before each experiment Baroreceptor threshold pressure (PtJ was higher in hypertensives (78 ±4 mm Hg) compared with normotensives (55 ±3 mm Hg, p<0.05), and nerve activity was less in hypertensives over a wide range of pressure. CS distensibility (sonomicrometers) was not significantly different in the two groups. After increasing holding pressure from control by 30 and 60 mm Hg for 10-15 minutes, the extent of baroreceptor resetting (A P^/A holding pressure x 100%) in normotensives was 39±6% and 33±2%, respectively, but only 14±5% and 9±3% in hypertensives (p<0.05). After decreasing holding pressure by 30 and 60 mm Hg, resetting was similar in normotensives (32±6% and 28±3%) and hypertensives (34±3% and 30±4%). In hypertensive rabbits, acute (10-15 minutes) exposure of baroreceptors to normotension (71 ± 4 mm Hg) decreased Pa, to 62 ±4 mm Hg and increased nerve activity to levels not significantly different from those of normotensive animals without altering CS distensibility. The results indicate that in chronic renal hypertension: 1) further upward resetting of baroreceptors during acute increases in pressure is suppressed; 2) in contrast, downward resetting during acute decreases in pressure is preserved; 3) baroreceptor activity is restored rapidly after brief exposure of the CS to normal pressure; and 4) changes in CS distensibility do not explain decreased baroreceptor activity in chronic hypertension nor restoration of activity after acute normalization of pressure. Impairment of acute upward resetting and preservation of downward resetting should be beneficial since they would oppose further increases in pressure and facilitate lowering of pressure. (Hypertension 1991;17:72-79) B aroreceptors buffer fluctuations in arterial pressure by causing reflexly mediated reciprocal changes in both heart rate and sympathetic nerve activity. 1 These changes keep the level of arterial pressure at a predetermined operating level or set point. When changes in pressure are sustained for several minutes, however, baroreceptors are reset rapidly and the baroreceptor pressure-activity curve shifts in the direction of pressure change to function at a new set point. 2 -5 This allows baroreceptors to buffer fluctuations of arterial pressure effectively because the new pressure set point remains on the steep portion of the reset pressure-activity curve. However, resetting provides positive feedback in the control of arterial pressure. During acute hypotension, baroreceptor activity increase...

Effects of antihypertensive agents on arterial baroreceptor reflexes in conscious rats.

“…44 However, it has been recently demonstrated that without increasing the arterial compliance, a brief period of normalization of blood pressure results in restoration of baroreceptor function. 45 Furthermore, as noted previously, 46 at 10 weeks of age the aortic wall characteristics of SHR and WKY rats are equivalent. This notion is supported by other investigators, 47 who observed that baroreceptor reflex sensitivity increased with age in WKY rats and that the low baroreceptor reflex sensitivity was retained throughout 4-20 weeks of age in SHR.…”

Structural Changes in AMPA-Receptive Neurons in the Nucleus of the Solitary Tract of Spontaneously Hypertensive Rats

“…One puzzling aspect of these studies is that the morphological changes seen in the SHR are consistent with an increase in glutamatergic synaptic activity, not a decrease. Aortic baroreceptors are known to reset 36 and thus are thought to decrease their activity during hypertension. However, the long-term consequences of hypertension on baroreceptor afferents are not fully understood, nor are the central changes in response to alterations in afferent activity.…”

Baroreflex sensitivity, blood pressure buffering, and resonance: what are the links? Computer simulation of healthy subjects and heart failure patients

“…At the baroreceptors, the systolic blood pressure S n is compared with a low-pass filtered systolic blood pressure reference value. This value functions as a dynamic blood pressure set point, mimicking the physiological process of baroreceptor resetting (47,50,51). The pressure variability source is added at the input of the baroreflex, rendering a sample-and-hold systolic blood pressure variability signal SBP, the first model output signal.…”

“…On the one hand, neural control of blood pressure by sympathetically induced vasoconstriction is relatively fast (seconds). On the other hand, baroreceptor resetting (47,50,51) limits the maximal duration during which baroreflex mediated buffering of a stressor may continue. In our simulations, the BPV frequency characteristics in Fig.…”