Nucleus Tractus Solitarii (NTS): Does It Mask the Interaction of Blood Pressure and Thermal Energetics?

Abstract

It is generally accepted that sino-aortic (SA) baroreceptor reflexes are “reset” in both experimental and clinical forms of arterial hypertension. In the unanesthetized endotherm these reflexes tonically inhibit medullary vasomotor centres whose function is most often considered in the context of circulatory homeostasis: Elevation of systemic arterial blood pressure (BP) activates SA mechanoreceptors and elicits neurogenically mediated compensatory reductions in heart rate and peripheral vasomotor tone (1). It is less well acknowledged that circulation is quite responsive to even mild thermal demands and controls thermogenic effector systems. In a cool (10–15°C) environment most normoten-sive endotherms, including humans, exhibit tonic increases in cardiac output, stroke volume, and mean aortic BP that are associated with proportionally greater elevations in total body oxygen consumption (2–8). Such cardiovascular responses are part of a more general hemodynamic adjustment designed to coregulate the nutritive and heat dissipating functions of circulation.