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Departments of Medicine (Cardiology) and Cellular and Molecular Physiology, General Clinical Research Center, Pennsylvania State University College of Medicine, The Milton S. Hershey Medical Center, Hershey, Pennsylvania 17033; and Department of Exercise Science, University of Georgia, Athens, Georgia 30602
The purpose of the
present study was to determine sympathetic vascular transduction in
young normotensive black and white adults. We hypothesized that blacks
would demonstrate augmented transduction of muscle sympathetic nerve
activity (MSNA) into vascular resistance. To test this hypothesis,
MSNA, forearm blood flow, heart rate, and arterial blood pressure were
measured during lower body negative pressure (LBNP). At rest, no
differences existed in arterial blood pressure, heart rate, forearm
blood flow, and forearm vascular resistance (FVR). Likewise, LBNP
elicited comparable responses of these variables for blacks and whites.
Baseline MSNA did not differ between blacks and whites, but whites
demonstrated greater increases during LBNP (28 ± 7 vs. 55 ± 18%, 81 ± 21 vs. 137 ± 42%, 174 ± 81 vs. 556 ± 98% for 
5, 15, and 40 mmHg LBNP, respectively;
P < 0.001). Consistent with smaller increases in MSNA
but similar FVR responses during LBNP, blacks demonstrated greater
sympathetic vascular transduction (%FVR/%MSNA) than whites (0.95 ± 0.07 vs. 0.82 ± 0.07 U; 0.82 ± 0.11 vs. 0.64 ± 0.09 U; 0.95 ± 0.37 vs. 0.35 ± 0.09 U; P < 0.01). In summary, young whites demonstrate greater increases in MSNA
during baroreceptor unloading than age-matched normotensive blacks.
However, more importantly, for a given increase in MSNA, blacks
demonstrate greater forearm vasoconstriction than whites. This finding
may contribute to augmented blood pressure reactivity in blacks.
autonomic nervous system; blood flow; hypertension; vascular resistance; stress reactivity; racial differences
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