Increased Sympathetic Nerve Activity Following Resection of Coarctation of the Thoracic Aorta

Twenty patients who underwent resection of the thoracic aorta and six patients operated on for hiatial hernia, patent ductus, mitral insufficiency, or A-V fistula were studied to determine whether there was an increase in sympatho-adrenal medullary activity following resection. Daily 24-hour urine samples were collected from each patient and control, and outputs of noradrenaline (norepinephrine) and adrenaline (epinephrine) were determined. The preoperative outputs were similar in the coarctation group and the controls. Postoperatively, however, although noradrenaline was elevated in both groups, it was elevated more in the coarctation group and remained elevated for a longer period than in the control subjects. Both the subjects with coarctation and the controls had marked increases in urinary output of adrenaline after operation. In the coarctation group, however, the increase was greater and extended for a longer period. The mechanism for increase in noradrenaline output seems to be directly related to the baroreceptors. After resection of aorta for coarctation, pressure in the proximal segment of the aorta decreases. The proximal baroreceptors then reduce their inhibitory influence on the bulbar vasomotor centers, and these centers, in order to compensate for the decreased proximal blood pressure, increase sympathetic nerve activity which is reflected by an increased release of noradrenaline.