What sets the long-term level of sympathetic nerve activity: is there a role for arterial baroreceptors?

Abstract

Malpas, Simon C. What sets the long-term level of sympathetic nerve activity: is there a role for arterial baroreceptors? Am J Physiol Regul Integr Comp Physiol 286: R1-R12, 2004; 10.1152/ajpregu.00496.2003.-Much of our knowledge of the influence of the sympathetic nervous system on the control of blood pressure is built on experimental approaches that focus very much on time scales Ͻ24 h. Although direct recordings of sympathetic nerve activity (SNA) over short time scales provide important information, it is difficult to place their relevance over the longer term where the development of chronic changes in blood pressure are likely to be a mixture of hormonal, renal, and neural influences. Recently new experimental approaches are now revealing a possible role for arterial baroreceptors in the chronic regulation of SNA. These studies reveal that chronic increases in blood pressure are associated with chronic changes in SNA that may be due to nonresetting of the blood pressure-SNA baroreflex relationship. This review discusses the implications of such information, highlighting new technologies for long-term recording of SNA that appear to hold much promise for revealing the role of SNA to the kidney for the long-term control of blood pressure. blood pressure; baroreflex; renal THE CONTROL OF ARTERIAL PRESSURE is a complex mixture of the long-and short-term influences of hormones, local vascular factors, and neural mechanisms. With regard to neural influences, much progress has been made in recent years on the central nervous system pathways involved in regulating sympathetic nerve activity (SNA) and the effect of that activity on vascular resistance. However, our knowledge of this control is mostly confined to short time scales of seconds and minutes, with a paucity of studies extending their focus to the longer term aspects (Ͼ24 h). Yet such information is liable to be critical in understanding the pathogenesis of hypertension where the onset of the disease is most likely to be a combination of slowly developing factors. As new tools for assessing sympathetic activity over longer time scales emerge, there is a growing desire and ability to understand longer term aspects of the regulation of SNA. It is recognized that pathways involved in regulating blood volume, osmolarity, and oxygen levels, as well as chronic changes in central nervous system function, are all likely to be important factors in understanding how SNA is controlled. However, given the revival in the hypothesis that arterial baroreflexes play a role in regulating the long-term levels of blood pressure, this review concentrates on the recent research supporting this concept. HISTORY

Sustained suppression of sympathetic activity and arterial pressure during chronic activation of the carotid baroreflex

“…Because technical limitations have precluded an understanding of the role of baroreflexes in long-term control of sympathetic activity and arterial pressure, the present findings are particularly important because they present a perspective that is diametrically opposite from studies using SAD. Furthermore, they are consistent with emerging evidence that the natural activation of the baroreflex in hypertension has sustained effects on cardiovascular function by chronically inhibiting sympathetic activity (1,13,17,19).…”

“…Both modifications were based on the arterial pressure and sympathetic responses to SAD, the most commonly used approach for studying the role of the baroreflex in long-term control of arterial pressure. The transient sympathetic activation and hypertension following SAD are often interpreted to indicate the unimportance of baroreflexes in long-term control of arterial pressure (4,13,17,19). In marked contrast, studies during 1 wk of electrical stimulation of the carotid sinus demonstrate a sustained effect of baroreflex activation to suppress sympathetic activity and arterial pressure.…”

Influence of Prolonged Baroreflex Activation on Arterial Pressure in Angiotensin Hypertension

“…In this regard, there has been a long-standing controversy as to whether baroreflexes play a role in the pathogenesis of hypertension. 9,13,14 This controversy stems from the paucity of techniques available to assess the long-term effects of the baroreflex on sympathetic activity, organ function, and arterial pressure. Solid arguments have been advanced to discount the role of baroreflexes in long-term control of sympathetic activity and arterial pressure.…”

Calculation of threshold and saturation points of sigmoidal baroreflex function curves

“…We propose that these be used as the standard equations for calculating threshold and saturation values when a logistic sigmoid function is used to model the open-loop baroreflex function curve. mathematical modeling; input-output relationship; baroreflex operating range; regression analysis THE BARORECEPTOR REFLEX is the major feedback control system regulating arterial blood pressure in the short term (5,14), and possibly also in the longer term (15,27). Numerous studies in humans and animals have demonstrated that the baroreceptor reflex can be reset under physiological conditions such as exercise (6 -8, 12, 17, 19 -24, 26, 28), sleep (18), heat stress (3), or pregnancy (4) and also pathological conditions such as hypertension (9,11) and cardiovascular deconditioning (10).…”