Sodium balance and the reflex regulation of baroreceptor function

The study of the mechanisms by which variations in salt intake affect cardiovascular function has progressed from characterizing hemodynamic and renal effects to investigating the role of sodium (Na+) on sympathetic neuronal function. The consequences of altered sodium balance on the regulation of vasomotor activity and the integration of baroreceptor reflexes is a relatively neglected area of research. This report summarizes the significance of the disturbance in baroreceptor function that is associated with alterations in Na+ homeostasis and assesses the possible mechanisms in a study of the interaction of the carotid sinus and vagal afferent reflexes in dogs exposed to sodium depletion or sodium loading. We also discuss the relationship between acute changes in cerebrospinal fluid Na+ concentration and sympathetic nerve activity in both the absence and presence of cardiopulmonary reflexes and after blockade of the systemic effects of vasopressin. The studies provide important evidence for a previously unsuspected action of Na+ upon the central circuits involved in integrating the interaction between low- and high-pressure baroreflexes.