Acute NaCl Loading Reveals a Higher Blood Pressure for a Given Serum Sodium Level in African American Compared to Caucasian Adults

Megan M Wenner, Erin P Paul, Austin T Robinson, William C Rose, William B Farquhar, Megan M Wenner, Erin P Paul, Austin T Robinson, William C Rose, William B Farquhar

Abstract

Purpose: African American individuals are more prone to salt-sensitive hypertension than Caucasian individuals. Small changes in serum sodium (Na+) result in increased blood pressure (BP). However, it remains unclear if there are racial differences in BP responsiveness to increases in serum Na+. Therefore, the purpose of this investigation was to determine if African American adults have altered BP responsiveness to acute changes in serum Na+ compared to Caucasian adults. Methods: We measured beat-by-beat BP, serum Na+, plasma renin activity (PRA), angiotensin II (Ang II), and aldosterone (Aldo) during a 60-min 3% NaCl infusion (hypertonic saline infusion, HSI) in 39 participants (19 African Americans, age: 23 ± 1, 20 Caucasians, age: 25 ± 1). Data reported as African American vs. Caucasian cohort, mean ± SEM. Results: Baseline BP and serum Na+ were similar between groups and increased during HSI in both African American and Caucasian participants (p < 0.01). However, the peak change in serum Na+ was greater in African American participants (Δ5.8 ± 0.34 vs. Δ4.85 ± 0.38 mmol/L, p = 0.03). There was a significant group effect (p = 0.02) and an interaction between race and serum Na+ on systolic BP (p = 0.02). Larger categorical changes in serum Na+ corresponded to changes in systolic BP (p < 0.01) and African American participants demonstrated greater systolic BP responses for a given categorical serum Na+ increase (p < 0.01). Baseline Aldo was lower in African American adults (7.2 ± 0.6 vs. 12.0 ± 1.9 ng/dL, p = 0.03), there was a trend for lower baseline PRA (0.59 ± 0.9 vs. 1.28 ± 0.34 ng/mL/h, p = 0.07), and baseline Ang II was not different (14.2 ± 1.8 vs. 18.5 ± 1.4 pg/mL, p = 0.17). PRA and Aldo decreased during the HSI (p ≤ 0.01), with a greater decline in PRA (Δ-0.31 ± 0.07 vs. Δ-0.85 ± 0.25 ng/mL/h, p < 0.01) and Aldo (Δ-2.5 ± 0.5 vs. Δ-5.0 ± 1.1 ng/dL, p < 0.01) in Caucasian participants. However, the racial difference in PRA (p = 0.57) and Aldo (p = 0.59) reduction were no longer significant following baseline covariate analysis. Conclusion: African American individuals demonstrate augmented serum Na+ to an acute hypertonic saline load and greater systolic BP responsiveness to a given serum Na+. The altered BP response may be attributable to lower basal PRA and Aldo and a subsequently blunted RAAS response during the HSI.

Keywords: RAAS; blood pressure; hypertonic saline; osmolality; race.

Figures

FIGURE 1
FIGURE 1
The influence of race and serum Na+ on systolic BP. At a given serum Na+, African American adults had a greater systolic BP. Statistically significant main effects and interaction listed on graph; all p < 0.05. Data presented as mean ± SEM.
FIGURE 2
FIGURE 2
(A) Systolic BP changes corresponding to different categorical levels of changes in serum sodium; and (B) proportion of categorical serum sodium changes for African American and Caucasian participants. Statistically significant main or interaction effect where p < 0.05. Data presented as mean ± SEM.
FIGURE 3
FIGURE 3
Renin-angiotensin-aldosterone system (RAAS) response to HSI. (A) PRA (African American n = 16, Caucasian n = 12) measured at baseline and throughout the HSI (top panel) and peak responses (bottom); (B) Aldo (African American n = 18, Caucasian n = 20) measured at baseline and throughout the HSI (top panel) and peak responses (bottom); and (C) Ang II (African American n = 16, Caucasian n = 12) measured at baseline and throughout the HSI (top panel) and peak responses (bottom). African American participants are represented in closed circles (•) and Caucasian participants in open circles (∘). Statistically significant main or interaction effect where p < 0.05. Data presented as mean ± SEM.

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