Young, non-Hispanic Black men and women exhibit divergent peripheral and cerebral vascular reactivity.

NEW FINDINGS: What is the central question of the study? Do peripheral and cerebral vascular function differ between young non-Hispanic Black men and women? What is the main finding and its importance? The non-Hispanic Black women in this study presented greater peripheral conduit artery and cerebrovascular reactivity, yet similar peripheral microvascular function relative to the non-Hispanic Black men. These preliminary findings suggest that young Black women and men possess divergent vascular function, possibly contributing to the unique non-Hispanic Black sex differences in cardiovascular and cerebrovascular diseases. ABSTRACT: In the USA, cardiovascular and cerebrovascular diseases remain more prominent in the non-Hispanic Black (BL) population relative to other racial/ethnic groups. Typically, sex differences emerge in the manifestation of these diseases, though these differences may not fully materialize in the BL population. While numerous mechanisms are implicated, differences in vascular function likely contribute. Research has demonstrated blunted vasodilatation in several vascular regions in BL versus non-Hispanic White individuals, though much of this work did not assess sex differences. Therefore, this study aimed to ascertain if indices of vascular function are different between young BL women (BW) and men (BM). Eleven BW and 15 BM (22 (4) vs. 23 (3) years) participated in this study. Each participant underwent testing for brachial artery flow-mediated dilatation (FMD), post-occlusive reactive hyperaemia and cerebral vasomotor reactivity during rebreathing-induced hypercapnia. BW exhibited greater adjusted FMD than BM (P < 0.05 for all), but similar or lower reactive hyperaemia when assessed as blood velocity (P > 0.39 for all) or blood flow reactivity (P < 0.05 for all), respectively. Across a range of hypercapnia, BW had greater middle cerebral artery blood velocity and cerebrovascular conductance index than BM (P < 0.001 for both). These preliminary data suggest that young BW have greater vascular function relative to young BM, though this was inconsistent across different indices. These findings provide insight into the divergent epidemiological findings between BM and BW. Further research is needed to elucidate possible mechanisms and relate these physiological responses to epidemiological observations.

Blunted hyperemic response to mental stress in young, non-Hispanic black men is not impacted by acute dietary nitrate supplementation.

Non-Hispanic black individuals suffer from an elevated prevalence of hypertension and cardiovascular disease (CVD) relative to other populations. This elevated disease risk is, in large part, related to impaired vascular function, secondary to reduced nitric oxide (NO) bioavailability. Emerging evidence suggests that dietary nitrate supplementation improves several cardiovascular parameters, including vascular function, in part by increased NO bioavailability. However, whether these findings extend to a population of black individuals is unknown. This study tested the hypothesis that forearm blood flow responses in young, non-Hispanic, black (BL) men during a mental stress challenge would be blunted relative to young, non-Hispanic, white (WH) men. We further hypothesized that acute dietary nitrate supplementation would improve this response in BL men. This study comprised two parts (phase 1 and phase 2). Phase 1 investigated the difference in blood flow responses between young, BL, and WH men. In contrast, phase 2 investigated the effect of acute nitrate supplementation on the responses in a subset of the BL men from phase 1. Eleven (nine for phase 2) BL and eight WH men (23 ± 3 vs. 24 ± 4 yr, respectively) participated in this double-blind, placebo-controlled, randomized, crossover study. During each visit, hemodynamic responses during 3 min of mental stress were assessed in the brachial artery using duplex Doppler ultrasound. Phase 1 was completed in one visit, whereas phase 2 was completed over two visits separated by ∼1 wk. During phase 2, data were collected before and 2-h postconsumption of a beverage either high in nitrate content or nitrate depleted. In phase 1, peak forearm blood flow (FBF; P < 0.001), total FBF (P < 0.01), and forearm vascular conductance (FVC; P < 0.001) were blunted in the BL. During phase 2, prebeverage responses were similar to phase 1 and were unaffected following beverage consumption (P > 0.05 vs. prebeverage for all variables). These data indicate that young, BL men have blunted microvascular vasodilatory responses to acute mental stress, which may not be altered following acute nitrate supplementation.NEW & NOTEWORTHY This study tested the hypothesis that non-Hispanic black (BL) men have a blunted forearm hyperemic response to mental stress, which would be augmented following acute nitrate supplementation. The increase in forearm blood flow during mental stress was attenuated in BL men and was not impacted by nitrate supplementation. This supports findings of altered vascular function in this population. This is especially important as BL experience a higher prevalence of stress, which contributes to CVD risk.

Fast-food meal reduces peripheral artery endothelial function but not cerebral vascular hypercapnic reactivity in healthy young men.

Consumption of a representative fast-food meal (FFMeal) acutely impairs peripheral conduit artery vascular function; however, the effect on cerebral vascular function remains unknown. This study tested the hypothesis that a FFMeal would impair cerebral vascular function as indexed by an attenuated increase in cerebral vascular conductance (CVCI) in the middle cerebral artery (MCA) during a hypercapnic challenge. Ten healthy men (age: 24 ± 3 years, BMI: 24.3 ± 3.8 kg/m2 ) were studied under two conditions; a standardized FFMeal (990 kcals, 50% fat, 36% carbohydrate, 14% protein, and 2120 mg sodium) and a fasting control condition. Basal hemodynamics, cerebral vasomotor reactivity (CVMR), and brachial artery flow-mediated dilation (BA FMD) were completed after an overnight fast (Pre) and again 2 h and 4 h later both days. To assess CVMR, subjects rebreathed from a 5-L bag while MCA velocity (MCAVmean ) was measured using transcranial Doppler (TCD) ultrasound and converted into CVCI (MCAVmean /mean arterial pressure). Peripheral artery endothelial function was assessed via BA FMD following a standard 5-min occlusion protocol. As expected, BA FMD was reduced at 2 h (Pre: 6.6 ± 1.7% vs. 5.2 ± 1.8%, P = 0.01). However, despite significant impairment in BA FMD, neither peak CVCI%baseline nor CVMR was affected by the FFMeal (Control-Pre: 1.9 ± 1.1, 2 h: 2.1 ± 1.1, 4 h: 1.7 ± 1.1 ∆CVCI%·∆PET CO2-1 vs. FFMeal-Pre: 2.1 ± 1.1, 2 h: 2.2 ± 0.7, 4 h: 1.9 ± 0.9 ∆CVCI%·∆PET CO2-1 , time × condition P = 0.88). These results suggest that cerebral vascular reactivity to hypercapnia in healthy young men is not altered by an acute FFMeal.

Sex differences in the mechanisms mediating blunted cutaneous microvascular function in young black men and women.

The black population exhibits attenuated vasodilatory function across their lifespan, yet little is known regarding the mechanisms of this impairment. Recent evidence suggests a potential role for oxidative stress. Therefore, we tested the hypothesis that NADPH oxidase (NOX) and/or xanthine oxidase (XO) contribute to blunted nitric oxide (NO)-mediated cutaneous microvascular function in young black adults. In 30 white and black subjects (8 men and 7 women in each group), local heating was performed while NOX and XO were inhibited by apocynin and allopurinol, respectively, via intradermal microdialysis. The plateau in cutaneous vascular conductance (red blood cell flux/mean arterial pressure) during 39°C local heating at each site was compared with a control site perfused with lactated Ringer solution. Subsequent inhibition of NO synthase via Nω-nitro-l-arginine methyl ester allowed for quantification of the NO contribution to vasodilation during heating. Black individuals, relative to white individuals, had a blunted cutaneous vascular conductance plateau at the control site (45 ± 9 vs. 68 ± 13%max, P < 0.001) that was increased by both apocynin (61 ± 15%max, P < 0.001) and allopurinol (58 ± 17%max, P = 0.005). Black men and black women had similar responses to heating at the control site ( P = 0.99), yet apocynin and allopurinol increased this response only in black men (both P < 0.001 vs. control). The NO contribution was also increased via apocynin and allopurinol exclusively in black men. These findings suggest that cutaneous microvascular function is reduced because of NOX and XO activity in black men but not black women, identifying a novel sex difference in the mechanisms that contribute to blunted vascular responses in the black population. NEW & NOTEWORTHY We demonstrate that cutaneous microvascular responses to local heating are consistently reduced in otherwise healthy young black men and women relative to their white counterparts. Inhibition of NADPH oxidase and xanthine oxidase via apocynin and allopurinol, respectively, augments microvascular function in black men but not black women. These data reveal clear sex differences in the mechanisms underlying the racial disparity in cutaneous microvascular function.