Lynne Mackey

Impaired stress-induced pressure natriuresis increases cardiovascular load 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.

Adiposity Is Related to Gender Differences in Impaired Stress-Induced Pressure Natriuresis

Abstract—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.

P-131: Sex differences in stress induced pressure natriuresis in African-American youths

African-Americans are characterized by an increased prevalence of essential hypertension, with a greater prevalence for males than females. We have hypothesized that stress induced impaired sodium regulation contributes to disparity. Therefore, the purpose of this study was to examine the factors related to changes in urinary sodium excretion (UNaV) during an extended stress period in African-American youths. Methods: The 40 subjects were 21 males and 19 females aged 15 to 18 years. The subjects were placed on a controlled sodium intake (4,0006200 mg/day) for 3 days prior to testing to bring them into similar levels of sodium balance. The test was performed on the fourth day. It consisted of a two hour baseline period, a one hour stress period (competitive video game), and a two hour recovery period. The subjects were provided with water throughout the study. Urine samples were collected hourly and blood pressure (BP) each 15 minutes. Overall, U NaV increased from the baseline to the stress period (10 65 v 1368 mEq/hr; p,0.002) and decreased from stress to recovery (7 64 mEq/hr; p,0.0001). Systolic BP (SBP) increased from the baseline period to the stress period (115 610 v 119612 mm Hg; p,0.009) and decreased during the recovery period (112 610 mmHg; p,0.07). However, different patterns were observed for males and females. Females had significant increases in U NaV form baseline to stress (9 65 v 1469 mEq/hr; p,0.002), and a significant decrease during recovery (7 64 mEq/hr; p,0.0001). SBP did not increase during stress. In contrast, males did not show a significant change in U NaV during stress; however, they did show a significant increase in SBP (116 610 v 124611 mmHg; p,0.002) which was still elevated into the second hour of recovery (118 6 10 mmHg; P,0.01). In conclusion, these results are consistent with our hypothesis that stress induced impaired pressure natriuresis resulting in an increased BP load contributes to the increased prevalence of hypertension in African-American males.