title: Neural-humoral responses during head-up tilt in healthy young white and black women.
abstract: Young black women have higher prevalence of hypertension during pregnancy compared to white women, which may be attributable to differences in blood pressure (BP) regulation. We hypothesized that young normotensive black women would demonstrate augmented muscle sympathetic nerve activity (MSNA) and renal-adrenal responses to orthostasis. Fifteen white and ten black women (30 ± 4 vs. 32 ± 6 years; means ± SD) had haemodynamics and MSNA measured during baseline (BL), 30 and 60° head-up tilt (HUT), and recovery. Blood was drawn for catecholamines, direct renin, vasopressin, and aldosterone. BL brachial systolic BP (SBP: 107 ± 6 vs. 101 ± 9 mmHg) and diastolic BP (DBP: 62 ± 4 vs. 56 ± 7 mmHg) were higher in white women (both p < 0.05). Δ DBP (60° HUT-BL) was greater in black women compared to white (p < 0.05). Cardiac output and total peripheral resistance were similar between groups. MSNA burst frequency was higher in whites (BL: 16 ± 10 vs. 14 ± 9 bursts/min, main effect p < 0.05) and increased in both groups during HUT (60°: 39 ± 8 vs. 34 ± 13 bursts/min, p < 0.05 from BL). Noradrenaline was higher in white women during 60° HUT (60° HUT: 364 ± 102 vs. 267 ± 89 pg/ml, p < 0.05). Direct renin was higher and vasopressin and Δ aldosterone tended to be higher in blacks (BL, direct renin: 12.1 ± 5.0 vs. 14.4 ± 3.7 pg/ml, p < 0.05; BL, vasopressin: 0.4 ± 0.0 vs. 1.6 ± 3.6 pg/ml, p = 0.065; Δ aldosterone: -0.9 ± 5.1 vs. 3.8 ± 7.5 ng/ml; p = 0.069). These results suggest that young normotensive white women may rely on sympathetic neural activity more so than black women who have a tendency to rely on the renal-adrenal system to regulate BP during an orthostatic stress.
authors.affiliation: Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas Dallas, TX, USA ; Department of Internal Medicine, University of Texas Southwestern Medical Center Dallas, TX, USA ; Department of Biological Sciences, Northern Arizona University Flagstaff, AZ, USA.
authors.forename: Sara S
authors.initials: SS
authors.lastname: Jarvis
authors.affiliation: Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas Dallas, TX, USA ; Department of Internal Medicine, University of Texas Southwestern Medical Center Dallas, TX, USA.
authors.forename: Shigeki
authors.initials: S
authors.lastname: Shibata
authors.affiliation: Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas Dallas, TX, USA ; Department of Internal Medicine, University of Texas Southwestern Medical Center Dallas, TX, USA.
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Okada
authors.affiliation: Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas Dallas, TX, USA ; Department of Internal Medicine, University of Texas Southwestern Medical Center Dallas, TX, USA.
authors.forename: Benjamin D
authors.initials: BD
authors.lastname: Levine
authors.affiliation: Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas Dallas, TX, USA ; Department of Internal Medicine, University of Texas Southwestern Medical Center Dallas, TX, USA.
authors.forename: Qi
authors.initials: Q
authors.lastname: Fu
keywords: aldosterone; muscle sympathetic nerve activity; renin