Relationship of body composition to stress-induced pressure natriuresis in youth.

BACKGROUND: The contribution of stress to obesity-related cardiovascular disease is uncertain. The purpose of this study was to examine the influence of body composition on stress-induced pressure natriuresis. METHODS: Dual energy x-ray absorptiometry was performed in 127 African American and white youths to assess lean body mass (LBM), fat mass (FM), and total percentage of body fat (%BF). The stress protocol was comprised of a 2-h baseline period, 1-h video game competition stressor, and 2-h recovery period. Blood and urine samples were collected hourly and blood pressure (BP) was obtained at 15-min intervals. RESULTS: Both BP and urinary sodium excretion(U(Na)V) increased from baseline to stress and returned to prestress levels after stress (P = .001 for each). The BP levels and changes were positively correlated with LBM. In contrast, levels and changes in sodium excretion U(Na)V were inversely correlated with FM and %BM. Multiple regression analyses that included ethnicity, sex, angiotensin II (Ang II), and measures of body composition in the models indicated the following: a) LBM was the best predictor of stress systolic BP and independently contributed with ethnicity to stress diastolic BP; b) ethnicity was the only independent predictor of the stress-related change in systolic and diastolic BP; c) LBM was the only independent predictor of the change in BP from stress to recovery for both systolic and diastolic BP; and d) total percent body fat accounted for 11.2% of the variance of stress U(Na)V, with Ang II contributing an additional 6.1%. CONCLUSIONS: Based on the results of this study, ethnicity and body composition are related to stress-induced pressure natriuresis.

Adiposity is related to gender differences in impaired stress-induced pressure natriuresis.

The purpose of this study was to determine if there are gender differences in stress-induced pressure natriuresis and to examine the effects of adiposity on these differences. The subjects were 151 boys and 141 girls 15 to 18 years of age who underwent a 5-hour stress protocol (2-hour prestress, 1-hour stress, 2-hour poststress) after being brought into similar levels of sodium balance. The gender-by-condition interaction was significant for systolic and diastolic blood pressure (P=0.001 for both), and the effect of condition was significant for sodium excretion (P=0.001). Systolic blood pressure was higher for boys throughout the protocol (P=0.001 for each) and correlated with body mass index at each condition (range in r=0.28 to 0.35; P<0.001 for each). Hemodynamically, in boys body mass index was correlated with cardiac output during stress (r=0.23; P=0.006), which was correlated with systolic blood pressure (r=0.21; P=0.01). With respect to natriuresis, body mass index was inversely correlated with sodium excretion during stress (r=-0.22; P=0.008) and positively correlated with angiotensin II in a subsample of boys (n=89: r=0.31; P=0.003). The inverse correlation between angiotensin II and sodium excretion during stress approached significance (r=-0.17; P<0.06). Similar results were not observed for girls. In conclusion, gender differences in stress-induced pressure natriuresis appear to be related to the influence of adiposity on both blood pressure and natriuresis.

Impaired stress-induced pressure natriuresis increases cardiovascularload in African American youths.

BACKGROUND: We hypothesized that impaired stress-induced pressure natriuresis increases blood pressure (BP) load. METHODS: The 118 African American youths were brought into similar levels of sodium balance. The protocol consisted of a 2-h baseline period, a 1-h stress period (competitive video games), and a 2-h recovery period. RESULTS: Normal pressure natriuresis (n = 80) resulted from a resistance-mediated (r = 0.23; P <.03) increase in BP (P <.001). In contrast, impaired pressure natriuresis (n = 38), leading to an extended period of elevated BP (P <.05), resulted from a volume-mediated (r = 0.55; P <.002) increase in BP (P <.001). CONCLUSIONS: Impaired stress-induced pressure natriuresis may contribute to the development of essential hypertension, particularly in African Americans.