Sensory nerve-mediated and nitric oxide-dependent cutaneous vasodilation in normotensive and prehypertensive non-Hispanic blacks and whites

Oral contraceptive pill phase alters mechanisms contributing to cutaneous microvascular function in response to local heating

The purpose of this study was to investigate the effect of oral contraceptive pill (OCP) phase on in vivo microvascular endothelium-dependent vasodilation and contributions of nitric oxide (NO), cyclooxygenase (COX), and endothelial-derived hyperpolarizing factors (EDHFs). Participants completed two experimental visits in random order, during the 1) low and 2) high hormone phase of the OCP cycle. Endothelium-dependent dilation was assessed in the cutaneous microvasculature via local heating at four intradermal microdialysis sites treated with: 1) lactated Ringer's (control), 2) 10 mM ketorolac (Keto, COX inhibitor), 3) 50 mM tetraethylammonium (TEA, calcium-activated potassium channel inhibitor), and 4) 10 mM ketorolac + 50 mM TEA (Keto + TEA). Perfusion of 20 mM Nω-nitro-l-arginine methyl ester (l-NAME) at each site was used to quantify the l-NAME-sensitive component of dilation, suggesting NO contribution. There was no effect of OCP phase on endothelium-dependent dilation (P = 0.75) or the l-NAME-sensitive component of the response (P = 0.09, d = 0.7) at control sites. Inhibition of COX increased baseline blood flow regardless of OCP phase (all P < 0.01). Control and Keto sites elicited greater endothelium-dependent dilation than TEA and Keto + TEA sites in both phases (all P < 0.0001). During the low hormone phase, the l-NAME-sensitive component was greater at control compared with TEA sites (P < 0.01). During the high hormone phase, the l-NAME-sensitive component was greater at Keto compared with TEA sites (P < 0.01). Within-participant differences between control and Keto sites support a phase-dependent restraint of NO activity via COX pathways (P = 0.01). These findings demonstrate that the OCP phase affects underlying mechanistic pathways contributing to cutaneous microvascular endothelial function.NEW & NOTEWORTHY This study investigates the effect of OCP phase on in vivo microvascular endothelium-dependent vasodilation and explores underlying mechanisms. Present findings suggest OCP phase does not affect overall microvascular endothelium-dependent dilation but does affect the underlying mechanisms. In women using OCP, there is a robust reliance on EDHF pathways and the COX pathway moderates basal microvascular blood flow and demonstrates a phase-dependent restraint of the NO pathway.

Quantification and interpretation of nitric oxide-dependent cutaneous vasodilation during local heating

Human cutaneous microdialysis approaches for assessing nitric oxide (NO)-dependent blood flow include local heating (LH) of the skin until a plateau is reached, followed by infusion of a NO synthase inhibitor such as NG-nitro-l-arginine methyl ester (l-NAME); however, varied methods of quantifying and expressing NO-dependent vasodilation can obfuscate data interpretation and reproducibility. We retrospectively assessed NO-dependent vasodilation during LH to 39°C or 42°C, calculated as the 1) absolute contribution of the NO-dependent component (along with baseline and the non-NO-dependent component) to the total cutaneous vascular conductance (CVC) response to LH, normalized to maximal CVC (%CVCmax); 2) difference in %CVCmax (Δ%CVCmax) between the LH plateau and post-NO synthase inhibition (l-NAME plateau; Δ%CVCmax = LH plateau - l-NAME plateau); 3) percentage of the LH plateau attributable to Δ%CVCmax (%plateau = Δ%CVCmax/LH plateau × 100); and 4) %plateau when correcting for baseline. The LH plateaus during 39°C and 42°C were 48 ± 17%CVCmax (9 ± 5% baseline; 2 ± 4% non-NO dependent; 36 ± 15% NO dependent) and 88 ± 10%CVCmax (15 ± 8% baseline; 9 ± 10% non-NO dependent; 64 ± 13% NO dependent), respectively. The absolute contributions of the non-NO-dependent and NO-dependent components of the response (P < 0.0001) and the Δ%CVCmax (66 ± 14 vs. 38 ± 15%) were greater during 42°C compared with 39°C (all P ≤ 0.02); however, there were no differences between the two protocols in %plateau (75 ± 13 vs. 80 ± 10%; P = 0.57) or %plateauBL (88 ± 14 vs. 95 ± 8%; P = 0.31). For both protocols, the values were greater for %plateauBL versus Δ%CVCmax and %plateau (P ≤ 0.0001), and for %plateau versus Δ%CVCmax (P ≤ 0.05). Quantification of NO-dependent skin vasodilation responses to LH is dependent upon the mathematical approach and verbal description, which can meaningfully impact data interpretation and reproducibility.NEW & NOTEWORTHY Local heating protocols are commonly used in conjunction with intradermal microdialysis for assessing nitric oxide (NO)-dependent microvascular function in humans, but various methods used to quantify and describe NO-dependent vasodilation may impact data interpretation. We compared four approaches for quantifying NO-dependent cutaneous vasodilation during local heating at 39°C and 42°C. We identify discrepancies in calculated NO-dependent dilation responses that are dependent upon the mathematical approach and meaningfully impact data interpretation and reproducibility.

Racial Disparities in Anesthesia Care: A Systematic Review of Pain Management and Patient Outcomes

Racial disparities in healthcare are a prominent issue that needs to be addressed to improve the quality of care for all patients. There are several disparities and biases related to the perceived pain tolerance people of color (POC) patients have and their need for analgesics. These biases lead to inadequate pain management and decreased health outcomes. Our study aims to highlight these disparities and how they impact the care patients receive, specifically in the field of anesthesia. To conduct this study, a comprehensive systematic literature search was performed, articles were included and removed according to specific inclusion and exclusion criteria, and a systematic review was performed. Sixteen papers that met the inclusion and exclusion criteria were selected, and after data collection, correlations between POC and pain tolerance were assessed throughout the articles. The studies reviewed showed that there may be some correlation between racial background and perceived pain tolerance. While some studies found that racial disparities may negatively impact the care POC patients receive, others found that there was no correlation at all. Regardless, more studies need to be conducted to assess the factors influencing the treatment of POC in anesthesia.

The effect of endothelin a receptor inhibition and biological sex on cutaneous microvascular function in non-Hispanic Black and White young adults

The purpose of this study was to investigate whether endothelin-A receptor (ETAR) inhibition in non-Hispanic Black (NHB) and White (NHW) young adults depends on biological sex. We recruited females during low hormone (n = 22) and high hormone (n = 22) phases, and males (n = 22). Participants self-identified as NHB (n = 33) or NHW (n = 33). Participants were instrumented with two microdialysis fibers: (1) lactated Ringer's (control) and (2) 500 nM BQ-123 (ETAR antagonist). Local heating was used to elicit cutaneous vasodilation, and an infusion of 20 mM L-NAME to quantify NO-dependent vasodilation. At control sites, NO-dependent vasodilation was lowest in NHB males (46 ± 13 %NO) and NHB females during low hormone phases (47 ± 12 %NO) compared to all NHW groups. Inhibition of ETAR increased NO-dependent vasodilation in NHB males (66 ± 13 %NO), in both groups of females during low hormone phases (NHW, control: 64 ± 12 %NO, BQ-123: 85 ± 11 %NO; NHB, BQ-123: 68 ± 13 %NO), and in NHB females during high hormone phases (control: 61 ± 11 %NO, BQ-123: 83 ± 9 %NO). There was no effect for ETAR inhibition in NHW males or females during high hormone phases. These data suggest the effect of ETAR inhibition on NO-dependent vasodilation is influenced by biological sex and racial identity.

Inhibition of superoxide and iNOS augment cutaneous nitric oxide-dependent vasodilation in non-Hispanic black young adults

We assessed the combined effect of superoxide and iNOS inhibition on microvascular function in non-Hispanic Black and non-Hispanic White participants (n = 15 per group). Participants were instrumented with four microdialysis fibers: (1) lactated Ringer's (control), (2) 10 μM tempol (superoxide inhibition), (3) 0.1 mM 1400 W (iNOS inhibition), (4) tempol + 1400 W. Cutaneous vasodilation was induced via local heating and NO-dependent vasodilation was quantified. At control sites, NO-dependent vasodilation was lower in non-Hispanic Black (45 ± 9% NO) relative to non-Hispanic White (79 ± 9% NO; p < 0.01; effect size, d = 3.78) participants. Tempol (62 ± 16% NO), 1400 W (78 ± 12% NO) and tempol +1400 W (80 ± 13% NO) increased NO-dependent vasodilation in non-Hispanic Black participants relative to control sites (all p < 0.01; d = 1.22, 3.05, 3.03, respectively). The effect of 1400 W (p = 0.04, d = 1.11) and tempol +1400 W (p = 0.03, d = 1.22) was greater than tempol in non-Hispanic Black participants. There was no difference between non-Hispanic Black and non-Hispanic White participants at 1400 W or tempol + 1400 W sites. These data suggest iNOS has a greater effect on NO-dependent vasodilation than superoxide in non-Hispanic Black participants.

Contribution of sensory nerves to cutaneous reactive hyperaemia in non-Hispanic Black and White young adults

NEW FINDINGS

What is the central question of this study? Does cutaneous sensory nerve-mediated vasodilatation differ between non-Hispanic Black and White young adults? What is the main finding and its importance? The magnitude of cutaneous reactive hyperaemia is lower in non-Hispanic Black relative to non-Hispanic White young adults, but the overall sensory nerve contribution is the same, suggesting that sensory nerve function is similar in both non-Hispanic Black and White young adults.

ABSTRACT

The aim of this study was to assess cutaneous sensory nerve function, independent of nitric oxide, in non-Hispanic Black and White young adults. We tested the hypothesis that cutaneous reactive hyperaemia and sensory nerve-mediated vasodilatation would be lower in non-Hispanic Black young adults relative to non-Hispanic White young adults. Twenty-four participants who self-identified as non-Hispanic Black (n = 12) or non-Hispanic White (n = 12) were recruited. All participants underwent three bouts of reactive hyperaemia. An index of skin blood flow was measured continuously using laser-Doppler flowmetry at a control site and at a site treated with topical 4% lignocaine to inhibit sensory nerve function. Peak reactive hyperaemia was lower in non-Hispanic Black relative to non-Hispanic White participants (P < 0.001). Total reactive hyperaemia was lower in non-Hispanic Black [mean (SD); control, 4085 (955)%CVCmax  s; lignocaine, 2127 (639) percent maximal cutaneous vascular conductance * seconds, %CVCmax  s] relative to non-Hispanic White [control: 6820 (1179)%CVCmax  s; lignocaine, 3573 (712)%CVCmax  s] participants (P < 0.001 for both sites). There was no difference between groups for the calculated contribution of sensory nerves to either the peak [non-Hispanic Black, 25 (14)%; non-Hispanic White, 19 (13)%] or total reactive hyperaemic response [non-Hispanic Black, 48 (10)%; non-Hispanic White, 47 (10)%]. These data suggest that cutaneous reactive hyperaemia is lower in non-Hispanic Black young adults, but the sensory nerve contribution is similar in non-Hispanic Black and White young adults.

Endothelin A receptor inhibition increases nitric oxide-dependent vasodilation independent of superoxide in non-Hispanic Black young adults

Young non-Hispanic Black adults have reduced microvascular endothelial function compared with non-Hispanic White counterparts, but the mechanisms are not fully elucidated. The purpose of this study was to investigate the effect of endothelin-1 A receptor (ET_AR) and superoxide on cutaneous microvascular function in young non-Hispanic Black (n = 10) and White (n = 10) adults. Participants were instrumented with four intradermal microdialysis fibers: 1) lactated Ringer's (control), 2) 500 nM BQ-123 (ET_AR antagonist), 3) 10 μM tempol (superoxide dismutase mimetic), and 4) BQ-123 + tempol. Skin blood flow was assessed via laser-Doppler flowmetry (LDF), and each site underwent rapid local heating from 33°C to 39°C. At the plateau of local heating, 20 mM l-NAME [nitric oxide (NO) synthase inhibitor] was infused to quantify NO-dependent vasodilation. Data are means ± standard deviation. NO-dependent vasodilation was decreased in non-Hispanic Black compared with non-Hispanic White young adults (P < 0.01). NO-dependent vasodilation was increased at BQ-123 sites (73 ± 10% NO) and at BQ-123 + tempol sites (71 ± 10%NO) in non-Hispanic Black young adults compared with control (53 ± 13%NO, P = 0.01). Tempol alone had no effect on NO-dependent vasodilation in non-Hispanic Black young adults (63 ± 14%NO, P = 0.18). NO-dependent vasodilation at BQ-123 sites was not statistically different between non-Hispanic Black and White (80 ± 7%NO) young adults (P = 0.15). ET_AR contributes to reduced NO-dependent vasodilation in non-Hispanic Black young adults independent of superoxide, suggesting a greater effect on NO synthesis rather than NO scavenging via superoxide.NEW & NOTEWORTHY Endothelin-1 A receptors (ET_ARs) have been shown to reduce endothelial function independently and through increased production of superoxide. We show that independent ET_AR inhibition increases microvascular endothelial function in non-Hispanic Black young adults. However, administration of a superoxide dismutase mimetic alone and in combination with ET_AR inhibition had no effect on microvascular endothelial function suggesting that, in the cutaneous microvasculature, the negative effects of ET_AR in non-Hispanic Black young adults are independent of superoxide production.

Effects of biological sex and oral contraceptive pill use on cutaneous microvascular endothelial function and nitric oxide-dependent vasodilation in humans

The purpose of this study was to evaluate in vivo endothelial function and nitric oxide (NO)-dependent vasodilation between women in either menstrual or placebo pill phases of their respective hormonal exposure [either naturally cycling (NC) or using oral contraceptive pills (OCPs)] and men. A planned subgroup analysis was then completed to assess endothelial function and NO-dependent vasodilation between NC women, women using OCP, and men. Endothelium-dependent and NO-dependent vasodilation were assessed in the cutaneous microvasculature using laser-Doppler flowmetry, a rapid local heating protocol (39°C, 0.1 °C/s), and pharmacological perfusion through intradermal microdialysis fibers. Data are represented as means ± standard deviation. Men displayed greater endothelium-dependent vasodilation (plateau, men: 71 ± 16 vs. women: 52 ± 20%CVC_max, P < 0.01), but lower NO-dependent vasodilation (men: 52 ± 11 vs. women: 63 ± 17%NO, P = 0.05) compared with all women. Subgroup analysis revealed NC women had lower endothelium-dependent vasodilation (plateau, NC women: 48 ± 21%CVC_max, P = 0.01) but similar NO-dependent vasodilation (NC women: 52 ± 14%NO, P > 0.99), compared with men. Endothelium-dependent vasodilation did not differ between women using OCP and men (P = 0.12) or NC women (P = 0.64), but NO-dependent vasodilation was significantly greater in women using OCP (74 ± 11%NO) than both NC women and men (P < 0.01 for both). This study highlights the importance of directly quantifying NO-dependent vasodilation in cutaneous microvascular studies. This study also provides important implications for experimental design and data interpretation.NEW & NOTEWORTHY This study supports differences in microvascular endothelial function and nitric oxide (NO)-dependent vasodilation between women in low hormone phases of two hormonal exposures and men. However, when separated into subgroups of hormonal exposure, women during placebo pills of oral contraceptive pill (OCP) use have greater NO-dependent vasodilation than naturally cycling women in their menstrual phase and men. These data improve knowledge of sex differences and the effect of OCP use on microvascular endothelial function.

Microvascular endothelial function following cessation of long-term oral contraceptive pill use: A case report

NEW FINDINGS

What is the main observation in this case? The main observation of this case report is substantial improvement in cutaneous microvascular endothelial function after cessation of long-term use of a fourth-generation oral contraceptive pill. This improvement appears independent of relative changes in the contribution of nitric oxide. What insights does it reveal? Our findings suggest that cessation of long-term, fourth-generation oral contraceptive pill use improves endothelial function within 20 months of cessation.

ABSTRACT

The purpose of this case report was to evaluate in vivo endothelial function and nitric oxide (NO)-dependent vasodilatation before and after the cessation of long-term (11-12 years) fourth-generation oral contraceptive pill (OCP) use in one young, healthy and premenopausal woman. This retrospective analysis includes data from six experimental visits: three visits during months 133-144 of fourth-generation OCP use and three visits 19-22 months after OCP cessation. Endothelium-dependent and NO-dependent vasodilatation were assessed in the cutaneous microvasculature using laser-Doppler flowmetry, a rapid local heating protocol (39°C, 0.1°C/s) and pharmacological perfusion through intradermal microdialysis fibres. The participant had consistent medical history and lifestyle behaviours throughout both hormonal exposures. Data are presented as the mean (SD). Endothelium-dependent vasodilatation was 42 (10)% of site-specific maximal cutaneous vascular conductance (CVCmax ) during OCP use and 63 (10)%CVCmax after OCP cessation (49% increase). Nitric oxide-dependent vasodilatation was 70 (5)% contribution of NO during OCP use and 60 (15)%NO after OCP cessation (15% reduction). Baseline blood flow was greater after OCP cessation, but maximal blood flow was reduced. Data from this case report support a substantial increase in cutaneous microvascular endothelial function assessed via local heating after cessation of long-term use of a fourth-generation OCP, which does not appear to be attributable to increased NO bioavailability. Overall, these data suggest an improvement in endothelial and microvascular function after the cessation of long-term use of a fourth-generation OCP.

Women with a history of preeclampsia have preserved sensory nerve-mediated dilatation in the cutaneous microvasculature

NEW FINDINGS

What is the central question of this study? Are sensory nerve-mediated vasodilatation and the NO-dependent contribution to that response attenuated in the cutaneous microvasculature of women who have had preeclampsia? What is the main finding and its importance? Women who have had preeclampsia demonstrate attenuated microvascular endothelium-dependent dilatation compared to women with a history of uncomplicated pregnancy. However, there are no differences in sensory nerve-mediated vasodilatation between groups. This suggests that the neurogenic response is not altered following preeclampsia, and that the NO-dependent vasodilatation of the neurogenic response is not related to endothelium-dependent NO-mediated dilatation in these women.

ABSTRACT

Women who have had preeclampsia (PE) demonstrate microvascular endothelial dysfunction, mediated in part by reduced nitric oxide (NO)-dependent mechanisms. Localized heating of the skin induces a biphasic vasodilatation response: a sensory nerve-mediated initial peak, followed by a sustained endothelium-dependent plateau. We have previously shown that the endothelium-dependent plateau is attenuated in PE. However, it is unknown if the sensory nerve-mediated initial peak is similarly attenuated. Therefore, the purpose of this study was to examine the effect of PE history on sensory nerve-mediated vasodilatation and the NO-dependent contribution to that response. We hypothesized that PE would have an attenuated initial peak and a reduced NO-dependent contribution to that response compared to women with a history of normotensive pregnancy (healthy controls, HC). Nine HC (31 ± 4 years) and nine PE (28 ± 6 years) underwent a standard local heating protocol (42°C; 0.1°C s^-1 ). Two intradermal microdialysis fibres were placed in the skin of the ventral forearm for the continuous local delivery of lactated Ringer solution alone (control) or 15-mM N^G -nitro-l-arginine methyl ester for nitric oxide synthase (NOS) inhibition. Red blood cell flux was measured at each site by laser Doppler flowmetry (LDF). Cutaneous vascular conductance was calculated (CVC = LDF/mean arterial pressure) and normalized to maximum (%CVC_max ; 28-mM SNP + local heat 43°C). There were no differences in the initial peak between groups (HC: 79 ± 8 vs. PE: 80 ± 10%CVC_max ; P = 0.936). NOS inhibition attenuated the initial peak in both HC (57 ± 18% CVC_max ; P = 0.003) and PE (54 ± 10%CVC_max ; P = 0.002). However, there were no differences in the NO-dependent portion of the initial peak (HC: 23 ± 16 vs. PE: 24 ± 9%; P = 0.777). The local heating plateau (HC: 99 ± 4 vs. PE: 88 ± 7%CVC_max ; P = 0.001) and NO contribution to the plateau (HC: 31 ± 9 vs. PE: 17 ± 14%; P = 0.02) were attenuated in PE. There was no relation between NO-dependent dilatation in the initial peak and NO-dependent dilatation in the plateau across groups (R²  = 0.005; P = 0.943). Women who have had PE demonstrate attenuated microvascular endothelium-dependent dilatation. However, there are no differences in sensory nerve-mediated vasodilatation following PE, suggesting that the NO-dependent vasodilatation of the neurogenic response is not related to endothelium-dependent NO-mediated dilatation in these women.

TRPA1 channel activation with cinnamaldehyde induces cutaneous vasodilation through NOS, but not COX and KCa channel, mechanisms in humans

ABSTRACT

Transient receptor potential ankyrin 1 (TRPA1) channel activation induces cutaneous vasodilation in humans in vivo. However, the mechanisms underlying this response remains equivocal. We hypothesized that nitric oxide (NO) synthase (NOS) and Ca2+ activated K+ (KCa) channels contribute to the TRPA1 channel-induced cutaneous vasodilation with no involvement of cyclooxygenase (COX). Cutaneous vascular conductance (CVC) in 9 healthy young adults was assessed at four dorsal forearm skin sites treated by intradermal microdialysis with either: 1) vehicle control (98% propylene glycol + 1.985% dimethyl sulfoxide + 0.015% lactated Ringer solution), 2) 10 mM L-NAME, a non-selective NOS inhibitor, 3) 10 mM ketorolac, a non-selective COX inhibitor, or 4) 50 mM tetraethylammonium, a non-selective KCa channel blocker. Cinnamaldehyde, a TRPA1 channel activator, was administered to each skin site in a dose-dependent manner (2.9, 8.8, 26 and 80 %, each lasting ≥30min). Administration of ≥8.8% cinnamaldehyde increased CVC from baseline at the vehicle control site by as much as 27.4% [95 % confidence interval of 5.3] (P<0.001). NOS inhibitor attenuated the cinnamaldehyde induced-increases in CVC at the 8.8, 26.0, and 80.0% concentrations relative to the vehicle control site (all P≤0.05). In contrast, both the COX inhibitor and KCa channel blockers did not attenuate the cinnamaldehyde induced-increases in CVC relative to the vehicle control site for all concentrations (all P≥0.130). We conclude that in human skin in vivo, NOS plays a role in modulating the regulation of cutaneous vasodilation in response to TRPA1 channel activation with no detectable contributions of COX and KCa channels.

Na+-K+-ATPase plays a major role in mediating cutaneous thermal hyperemia achieved by local skin heating to 39°C

Na⁺-K⁺-ATPase is integrally involved in mediating cutaneous vasodilation during an exercise-heat stress, which includes an interactive role with nitric oxide synthase (NOS). Here, we assessed if Na⁺-K⁺-ATPase also contributes to cutaneous thermal hyperemia induced by local skin heating, which is commonly used to assess cutaneous endothelium-dependent vasodilation. Furthermore, we assessed the extent to which NOS contributes to this response. Cutaneous vascular conductance (CVC) was measured continuously at four forearm skin sites in 11 young adults (4 women). After baseline measurement, local skin temperature was increased from 33°C to 39°C to induce cutaneous thermal hyperemia. Once a plateau in CVC was achieved, each skin site was continuously perfused via intradermal microdialysis with either: 1) lactated Ringer solution (control), 2) 6 mM ouabain, a Na⁺-K⁺-ATPase inhibitor, 3) 20 mM l-NAME, a NOS inhibitor, or 4) a combination of both. Relative to the control site, CVC during the plateau phase of cutaneous thermal hyperemia (∼50% max) was reduced by the lone inhibition of Na⁺-K⁺-ATPase (-19 ± 8% max, P = 0.038) and NOS (-32 ± 4% max, P < 0.001), as well as the combined inhibition of both (-37 ± 9% max, P < 0.001). The magnitude of reduction was similar between NOS inhibition alone and combined inhibition (P = 1.000). The administration of both Na⁺-K⁺-ATPase and NOS inhibitors fully abolished the plateau of CVC with values returning to preheating baseline values (P = 0.439). We show that Na⁺-K⁺-ATPase contributes to cutaneous thermal hyperemia during local skin heating to 39°C, and this response is partially mediated by NOS.NEW & NOTEWORTHY Cutaneous thermal hyperemia during local skin heating to 39°C, which is highly dependent on nitric oxide synthase (NOS), is frequently used to assess endothelium-dependent cutaneous vasodilation. We showed that Na⁺-K⁺-ATPase mediates the regulation of cutaneous thermal hyperemia partly via NOS-dependent mechanisms although a component of the Na⁺-K⁺-ATPase modulation of cutaneous thermal hyperemia is NOS independent. Thus, as with NOS, Na⁺-K⁺-ATPase may be important in the regulation of cutaneous endothelial vascular function.

Inhibition of iNOS augments cutaneous endothelial NO-dependent vasodilation in prehypertensive non-Hispanic Whites and in non-Hispanic Blacks

We tested the hypothesis that inducible nitric oxide synthase (iNOS) contributes to reduced nitric oxide (NO)-dependent vasodilation in non-Hispanic Blacks and prehypertensive non-Hispanic Whites. Twenty Black and twenty White participants (10 normotensive, 10 prehypertensive per group; n = 40 total) participated in this study. Participants were instrumented with two microdialysis fibers, and each site was randomized as control (lactated Ringer) or iNOS inhibition (0.1 mM 1400W). Laser-Doppler flow probes and local heaters were used to measure skin blood flow and heat the skin to induce vasodilation, respectively. Each site was heated from 33°C to 39°C (rate: 0.1°C/s). Once a plateau was established, 20 mM nitro-l-arginine methyl ester (l-NAME), a nonspecific NOS inhibitor, was infused at each site to quantify NO-dependent vasodilation. At control sites, %NO-dependent vasodilation was reduced in prehypertensive Whites (47 ± 10%NO) and in both normotensive and prehypertensive Blacks (39 ± 9%NO and 28 ± 5%NO, respectively) relative to normotensive Whites (73 ± 8%NO; P < 0.0001 for all comparisons). Compared with respective control sites, iNOS inhibition increased NO-dependent vasodilation in prehypertensive Whites (68 ± 8%NO) and in both normotensive and prehypertensive Blacks (78 ± 8%NO and 55 ± 6%NO, respectively; P < 0.0001 for all comparisons). We failed to find an effect for normotensive Whites (77 ± 7%NO). After iNOS inhibition, %NO-dependent vasodilation was similar between normotensive Whites, prehypertensive Whites, and normotensive Blacks. Inhibition of iNOS increased NO-dependent vasodilation to a lesser extent in prehypertensive Blacks. These data suggest that iNOS contributes to reduced NO-dependent vasodilation in prehypertension and in Black participants.NEW & NOTEWORTHY Inducible nitric oxide synthase (iNOS) is typically upregulated in conditions of increased oxidative stress and may have detrimental effects on the vasculature. Endothelial nitric oxide (NO), which is cardioprotective, is reduced in prehypertensive non-Hispanic Whites and in non-Hispanic Blacks. We found that inhibition of iNOS can increase endothelial NO-dependent vasodilation in prehypertensive White participants and in both normotensive and prehypertensive Black participants.Inducible nitric oxide (NO) synthase (iNOS) can be upregulated under conditions of increased oxidative stress and may have detrimental effects on the vasculature. Endothelial NO, which is cardioprotective, is reduced in prehypertensive non-Hispanic Whites and in non-Hispanic Blacks. We found that inhibition of iNOS can increase endothelial NO-dependent vasodilation in prehypertensive White participants and in both normotensive and prehypertensive Black participants.

Four weeks of vitamin D supplementation improves nitric oxide-mediated microvascular function in college-aged African Americans

Reduced nitric oxide (NO)-mediated cutaneous vasodilation, secondary to increased oxidative stress, presents in young African American (AA) compared with European American (EA) adults and may be modulated by vitamin D status. We assessed cutaneous microvascular function in 18 young, healthy (21 ± 2 yr; 9 men, 9 women) subjects before (pre, 8 AA, 10 EA) 4 wk of 2,000 IU/day oral vitamin D supplementation and in 13 subjects after (post, 7 AA, 6 EA) 4 wk of 2,000 IU/day oral vitamin D supplementation. Serum vitamin D concentrations [25(OH)D] were measured at each visit. Three intradermal microdialysis fibers placed in the ventral forearm were randomized for treatment with 10 μM Tempol, 100 μM apocynin, or lactated Ringer's solution (control). Local heating (39°C) induced cutaneous vasodilation; red cell flux was measured at each site (laser-Doppler flowmetry), and cutaneous vascular conductance (CVC = flux/MAP) was expressed as a percentage of maximum (28 mM sodium nitroprusside, +43°C) for each phase of local heating. After stable elevated blood flow was attained, 15 mM N^G-nitro-l-arginine methyl ester (l-NAME; NO synthase inhibitor) was perfused at all sites to quantify the NO contribution to cutaneous vasodilation (%NO), calculated as the difference between local heating and l-NAME plateaus. Serum [25(OH)D], the magnitude of the local heating response, and %NO were all lower in AAs versus EAs (P < 0.01). Tempol (P = 0.01), but not apocynin (P ≥ 0.19), improved the local heating response and %NO. Four weeks of supplementation improved serum [25(OH)D], the local heating response, and %NO in AAs (P ≤ 0.04) but not in EAs (P ≥ 0.41). Vitamin D supplementation mitigated endothelial dysfunction, an antecedent to overt cardiovascular disease (CVD), in otherwise healthy, young AA adults.NEW & NOTEWORTHY Endothelial dysfunction, an antecedent to overt cardiovascular disease (CVD), is observed earlier and more frequently in otherwise healthy African Americans (AAs) when compared with other ethnic groups. Vitamin D may modulate endothelial function, and darkened skin pigmentation increases risk of vitamin D deficiency. We show that 4 wk of 2,000 IU/day vitamin D supplementation improves microvascular responses to local heating in AAs. Ensuring adequate vitamin D status may mitigate development of cardiovascular dysfunction in this at-risk population.