Abstract 10682: Acute Vagal Stimulation Attenuates Cardiac Metabolic Response to Beta-adrenergic Stress in Chronically Instrumented Dogs
The interest for cardiac parasympathetic innervation has been recently revitalized by experimental and clinical evidence of a beneficial effect of cervical right vagus stimulation (VS) on failing hearts, which are notoriously under high sympathetic tone. However, the influence of VS on cardiac function and metabolism, especially in conditions of adrenergic stress, is still little understood. We tested the hypothesis that acute VS alters the balance between free fatty acid (FFA) and carbohydrate oxidation and opposes the metabolic effects of beta-adrenergic stimulation. A clinical-type selective stimulator of the vagal efferent fibers was connected to the intact right vagus in chronically instrumented dogs. VS was set to reduce heart rate by 30 beats/min, then the confounding effects of bradycardia were excluded by pacing the heart at 165 beats/min. 3H-oleate and 14C-glucose were infused and paired blood samples were withdrawn from aorta and coronary sinus to measure myocardial oxygen consumption, FFA and glucose oxidation and lactate uptake. External work was quantified by calculating the left ventricular pressure-diameter area (PDA). The heart was subjected to beta-adrenergic stress by infusing 5, 10 and 15 µg/kg/min of dobutamine before and during VS. We found that VS did not significantly affect baseline cardiac performance, hemodynamics and myocardial metabolism. However, at peak dobutamine stress, VS limited the increase 1) in left ventricular PDA from 235.9±72.8% to 167.3±55.8%, and in cardiac oxygen consumption from 173.9±23.3% to 127.9±6.2% (all P<0.05), therefore mechanical efficiency was not enhanced 2) in glucose oxidation from 0.024±0.004 to 0.013±0.003 µmol/beat, and in lactate uptake from 0.028±0.004 to 0.022±0.004 µmol/beat (all P<0.05). FFA oxidation was not increased by beta-adrenergic stress and fell below baseline during VS only at the lowest dose of dobutamine. The functional, but not the metabolic changes, were reversed by 0.01 mg/kg atropine I.V. Our data show, for the first time, that, while acute right VS does not affect baseline cardiac metabolism it attenuates myocardial oxygen consumption, glucose oxidation and lactate uptake in response adrenergic stress, thus functioning as a “cardio-selective beta-blocker”.
- © 2012 by American Heart Association, Inc.