Altered autonomic control or coronary artery blood flow by the aortic body chemoreceptors in conscious normotensive and hypertensive sheep

Abstract

Peripheral arterial chemoreceptors monitor the chemical composition of the blood. While, the carotid bodies located at the bifurcation of the common carotid arteries have been extensively studied. The physiological role of the aortic bodies located in the walls of the aortic arch remains relatively under-studied, and its role in hypertension is unexplored.We hypothesized that activation of the aortic bodies would increase coronary blood flow in the normotensive state and that the parasympathetic nerves to the heart would mediate this.Experiments were conducted in conscious and anesthetized ewes instrumented to record arterial pressure, coronary blood flow, and cardiac output. Two groups of animals were studied, one made hypertensive using a 2 kidney one-clip model (HTN. n=6) and a sham-clipped normotensive group (Con. n=6). Unilateral renal clipping increased resting mean arterial pressure (Con: 84±5 vs HTN 115±6 mmHg). The aortic body chemoreceptors were stimulated by a bolus infusion of potassium cyanide (KCN; 10-30 μg/kg) into the left ventricle.Activation of the aortic bodies in the normotensive and hypertensive animals resulted in a significant increase in coronary blood flow ( P<0.05, 2-way ANOVA, interaction effect), which was not different between groups. In normotensive sheep, the aortic body chemoreflex-mediated coronary vasodilation was attenuated by atropine infusion. Interestingly, the coronary vasodilation in hypertensive animals was not altered by the blockade of muscarinic receptors but was attenuated after propranolol infusion ( P<0.05, interaction effect). Bilateral vagotomy is not possible in conscious animals; under anesthesia, the coronary blood flow response to aortic body stimulation was significantly attenuated in normotensive sheep. Neither atropine nor propranolol affected the aortic body chemoreflex meditated changes in either group's blood pressure, heart rate, or cardiac output. This data suggests that the aortic bodies play an important role in modulating coronary blood flow and that their effector mechanism is altered in hypertension. Many patients with hypertension are on beta-blockers. Our finding indicates that the aortic bodies modulate coronary blood flow via a beta-adrenergic mechanism in hypertension, which may have important implications for regulating coronary blood flow during exertion in hypertensive patients. Work is supported by the Health Research Council (HRC) of New Zealand. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.