Aortic chemoreflex control of coronary blood flow and cardiovascular function in health and hypertension

Abstract

Aortic and carotid bodies are peripheral chemoreceptors that detect and respond to changes in arterial oxygen. Reflex responses by carotid bodies to hypoxia have been well characterized however, the functional significance of aortic bodies both in health and disease are largely unknown. Given their location in the walls of the aortic arch near the heart, the aortic bodies may have a specialized role in regulating coronary blood flow. The interest in coronary blood flow stems from its impaired regulation in hypertension though the exact mechanisms of this are unclear. We hypothesized that aortic body activation causes an increase in coronary blood flow in the healthy state and that this response is impaired in hypertension. This and the neural mechanisms responsible were examined in conscious normal sheep and sheep with induced renovascular hypertension by unilateral clipping of the renal artery. Aortic body stimulation with a small bolus of potassium cyanide infused into the left ventricle produced a dose-dependent increase in coronary blood flow that was overall mediated by coronary vasodilatation in both normal and hypertensive sheep. In normal sheep, the coronary vasodilatation was attenuated by atropine, indicating that it was parasympathetically-mediated. In hypertensive sheep, the response was attenuated by propranolol, indicating that it was sympathetically-mediated. The increase in coronary blood flow was not mediated by carotid bodies. Aortic bodies also produced an increase in cardiac output and an increase in respiratory drive comparable to carotid bodies. The mechanism for the shift in the coronary response by aortic bodies from being parasympathetically-mediated in health to sympathetically-mediated in hypertension is unclear. In this regard, a closer inspection of the use of β-adrenergic blockers on long term coronary perfusion may be necessary. Overall, our novel results suggest a specialized role of aortic bodies in maintaining adequate oxygen supply to the heart that is differentially mediated in health and hypertension.