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(Hypertension. 2006;48:120.)
© 2006 American Heart Association, Inc.

Original Articles

Influences of Norepinephrine Transporter Function on the Distribution of Sympathetic Activity in Humans

Antje F. Mayer; Christoph Schroeder; Karsten Heusser; Jens Tank; André Diedrich; Roland E. Schmieder; Friedrich C. Luft; Jens Jordan

From the Franz-Volhard Clinical Research Center (A.F.M., C.S., K.H., J.T., F.C.L., J.J.), Medical Faculty of the Charité, Max-Delbrueck Centrum, and HELIOS Klinikum, Berlin, Germany; Autonomic Dysfunction Service (A.D.), Vanderbilt University, Nashville, Tenn; and the Nephrology Research Laboratory (R.E.S.), University Erlangen-Nuremberg, Germany.

Correspondence to Jens Jordan, MD, Franz-Volhard-Clinical Research Center, Charité Campus Buch, Wiltbergstr. 50, Haus 129, 13125 Berlin, Germany. E-mail jordan{at}fvk.charite-buch.de

Previous studies suggest that neuronal norepinephrine transporter function may regulate the distribution of sympathetic activity among blood vessels, heart, and kidney; we tested the functional relevance in humans. Sixteen healthy men (26±1 years) ingested 8 mg of the selective norepinephrine reuptake transporter inhibitor reboxetine or a matching placebo on 2 separate days in a double-blind, randomized, crossover fashion. We monitored heart rate, thoracic bioimpedance, blood pressure, glomerular filtration rate, and renal blood flow. Ninety minutes after ingestion of the test medication, subjects were tilted to a 45° head-up position, where they remained for an additional 30 minutes. Reboxetine increased supine systolic blood pressure through an increase in cardiac output whereas systemic vascular resistance decreased. Furthermore, reboxetine increased heart rate, particularly with a head-up tilt. Supine plasma renin activity was 0.71±0.15 ng angiotensin (Ang)/L per mL/h with placebo and 0.36±0.07 ngAng/L per mL/h with reboxetine (P<0.01). Supine plasma Ang II concentrations were also decreased with reboxetine. Both plasma renin activity and Ang II concentrations remained suppressed during head-up tilt. On placebo, renal vascular resistance increased with head-up tilt. The response was abolished with norepinephrine reuptake inhibition. We conclude that norepinephrine reuptake function profoundly influences the distribution of sympathetic activity between the heart, vasculature, and kidney in humans. All of these changes are physiologically relevant because they lead to corresponding changes in organ function.

Key Words: sympathetic nervous system • norepinephrine • renal circulation • renin-angiotensin system

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