Oral atorvastatin therapy increases nitric oxide-dependent cutaneous vasodilation in humans by decreasing ascorbate-sensitive oxidants

Spectral changes in skin blood flow during pressure manipulations or sympathetic stimulation

Skin blood flow is commonly determined by laser Doppler flowmetry (LDF). It has been suggested that pathophysiological conditions can be assessed by analysis of specific frequency domains of the LDF signals. We tested whether physiological stimuli that activate myogenic and neurogenic mechanisms would affect relevant portions of the laser Doppler spectrum. LDF sensors were placed on the right forearm of 14 healthy volunteers for myogenic (six females) and 13 for neurogenic challenge (five females). Myogenic responses were tested by positioning the arm ∼50° above/below heart level. Neurogenic responses were tested by immersing the left hand into an ice slurry with and without topical application of local anaesthetic. Short-time Fourier analyses were computed over the range of 0.06 to 0.15 Hz for myogenic and 0.02 to 0.06 Hz for neurogenic. No significant differences in spectral density were observed (P = 0.40) in the myogenic range with arm above (7 ± 54 × 10-4 dB) and below heart (7 ± 14 × 10-4 dB). Neurogenic spectral density showed no significant increase from baseline to cold pressor test (0.0017 ± 0.0013 and 0.0038 ± 0.0039 dB; P = 0.087, effect size 0.47). After application of anaesthetic, neurogenic spectral density was unchanged between the baseline and cold pressor test (0.0014 ± 0.0025 and 0.0006 ± 0.0005 dB; P = 0.173). These results suggest that changes in the myogenic and neurogenic spectral density of LDF signals did not fully reflect the skin vascular function activated by pressure manipulation and sympathetic stimulation. Therefore, LDF myogenic and neurogenic spectral density data should be interpreted with caution.

Climate change and the prevention of cardiovascular disease

Climate change is a worsening global crisis that will continue negatively impacting population health and well-being unless adaptation and mitigation interventions are rapidly implemented. Climate change-related cardiovascular disease is mediated by air pollution, increased ambient temperatures, vector-borne disease and mental health disorders. Climate change-related cardiovascular disease can be modulated by climate change adaptation; however, this process could result in significant health inequity because persons and populations of lower socioeconomic status have fewer adaptation options. Clear scientific evidence for climate change and its impact on human health have not yet resulted in the national and international impetus and policies necessary to slow climate change. As respected members of society who regularly communicate scientific evidence to patients, clinicians are well-positioned to advocate on the importance of addressing climate change. This narrative review summarizes the links between climate change and cardiovascular health, proposes actionable items clinicians and other healthcare providers can execute both in their personal life and as an advocate of climate policies, and encourages communication of the health impacts of climate change when counseling patients. Our aim is to inspire the reader to invest more time in communicating the most crucial public health issue of the 21st century to their patients.

Seven days of statin treatment improves nitric-oxide mediated endothelial-dependent cutaneous microvascular function in women with endometriosis

INTRODUCTION

Endometriosis is associated with systemic inflammation and increased risk of cardiovascular disease (CVD). Endothelial dysfunction is one of the first manifestations of CVD but is unexplored in women with endometriosis. HMG-CoA-reductase inhibitors (statins) exert potent anti-inflammatory effects, and have been proposed as an adjunctive therapy in women with endometriosis. We hypothesized that microvascular endothelial function would be impaired in otherwise healthy women with endometriosis mediated by reduced nitric oxide (NO)-dependent dilation and that short term statin administration would improve endothelial function.

METHODS

In 8 healthy control (HC: 33 ± 9 yr) and 8 women with endometriosis (EN: 34 ± 9 yr), laser-Doppler flux (LDF) was measured continuously during graded intradermal microdialysis perfusion of the endothelium-dependent agonist acetylcholine (Ach: 10-10-10-1 M) alone and in combination with the NO synthase inhibitor (L-NAME: 0.015 M). 6 EN repeated the microdialysis experiment following 7 days of oral atorvastatin treatment (10 mg). Cutaneous vascular conductance was calculated (CVC = LDF*mmHg-1) and normalized to site-specific maximum (28 mM sodium nitroprusside, 43 °C). The NO-dependent dilation was calculated as the difference between the areas under the dose response curves.

RESULTS

Ach-induced vasodilation was blunted in women with endometriosis (main effect p < 0.01), indicating impaired endothelial function. NO-dependent vasodilation was also reduced in women with endometriosis (HC: 217 ± 120.3 AUC vs. EN: 88 ± 97 AUC, p = 0.03). Oral atorvastatin improved Ach-induced (main effect p < 0.01) and NO-dependent (295 ± 153 AUC; p = 0.05) vasodilation in women with endometriosis.

CONCLUSION

Microcirculatory endothelium-dependent vasodilation is impaired in women with endometriosis, mediated in part by reductions in NO. Short-term oral atorvastatin improved endothelium-dependent vasodilation, suggesting that statin therapy may be a viable intervention strategy to mitigate accelerated CVD risk in women with endometriosis.

Reactive hyperemia augments local heat-induced skin hyperemia

NEW FINDINGS

What is the central question of this study? It is valuable to be able to monitor disease or treatment related changes in the microcirculation. Laser doppler flowmetry with local heating allows noninvasive monitoring of the skin microcirculation and its ability to vasodilate. Does reactive hyperemia augment the increase in skin blood flow elicited by local heating? What is the main finding and its importance? The results of this study show that the addition of reactive hyperemia to local heating results in greater vasodilation than heating alone. Thus, reactive hyperemia can augment local heat-induced hyperemia in the skin.

ABSTRACT

The skin circulation has been proposed as a model of generalized microvascular function which could be monitored noninvasively using laser doppler flowmetry (LDF). The response to heat hyperemia (HH) is commonly used to monitor disease or treatment related changes in microvascular function. We hypothesized that reactive hyperemia would augment the increase in skin blood flow elicited by local heating. Fourteen healthy young adults were subjected to 3 different conditions: reactive hyperemia (RH; skin temperature controlled at 33°C), heat hyperemia (HH; 42°C held for 40 minutes), and HH+RH. Two Peltier-controlled thermomodules with laser LDF probes were placed on the right forearm to continuously monitor skin blood flow. A cuff was placed on the right upper arm to elicit RH by inflation to 220 mmHg for 5 minutes. This procedure was performed with skin temperature at 33°C and again after 40 min of local heating to 42°C. Beat-by-beat mean arterial pressure (MAP) obtained by a photoplethysmographic sensor on the middle finger of the left hand allowed calculation of cutaneous vascular conductance (CVC) as LDF / MAP. Both HH and RH increased LDF (p<0.0001 and p <0.0001, respectively) and CVC (p = 0.0001 and p<0.0001) above baseline values. LDF and CVC values were significantly higher during HH+RH when compared to RH or HH alone (p<0.0001). In summary, HH+RH resulted in greater vasodilation when compared to HH or RH alone. These results indicate that RH can augment local heat-induced hyperemia in the skin. This article is protected by copyright. All rights reserved.

Skin microvascular reactivity and subendocardial viability ratio in relation to dyslipidemia and signs of insulin resistance in non-diabetic hypertensive patients

OBJECTIVE

The aim of this study was to evaluate the influence of dyslipidemia and insulin resistance for the development of microvascular dysfunction in non-diabetic primary hypertension.

METHODS

Seventy-one patients with untreated primary hypertension were included. Skin microvascular reactivity was evaluated by laser Doppler fluxmetry with iontophoresis (acetylcholine, ACh and sodium nitroprusside, SNP) and heat-induced hyperemia. Myocardial microvascular function was estimated by the subendocardial viability ratio (SEVR) calculated from pulse wave analysis and applanation tonometry. Triglyceride x glucose (TyG index) and triglyceride/HDL cholesterol ratio were used as measurements of insulin resistance.

RESULTS

Skin microvascular dysfunction was associated with low HDL cholesterol, where Ach-mediated peak flux (r = .27, p = .025) and heat-induced peak flux (r = .29, p = .017) related to HDL cholesterol levels. ACh peak flux was inversely related to TG/HDL ratio (r = -.29, p = .016), while responses to local heating and SNP did not. SEVR did not relate to HDL and was unrelated to markers of insulin resistance. These findings were confirmed by multivariable analyses, including potential confounders.

CONCLUSIONS

Early microvascular dysfunction can be detected in non-diabetic hypertensive patients and is related to dyslipidemia and to signs of insulin resistance, thus predicting future cardiovascular risk.

Chronic statin therapy is associated with enhanced cutaneous vascular responsiveness to sympathetic outflow during passive heat stress

KEY POINTS

Impairments in both central sympathetic and peripheral microvascular function contribute to blunted reflex cutaneous vasodilatation during heat stress in healthy older adults. Hypercholesterolaemia is associated with decrements in neurovascular function; however, little is known about the impact of hypercholesterolaemia on the integrated responses to heat stress. Further, whether chronic statin therapy alters skin sympathetic outflow or its relation to cutaneous vascular conductance during heat stress is unknown. We demonstrate that reflex cutaneous vasodilatation is impaired in older hypercholesterolaemic adults but not in formerly hypercholesterolaemic adults currently treated with a statin compared to age-matched controls. Additionally, chronic statin treatment-induced improvements in reflex vasodilatation are mediated, in part, by increases in end-organ responsiveness to efferent sympathetic outflow during whole-body heating. These data add to the growing body of literature substantiating the beneficial pleiotropic neurovascular effects of chronic statin treatment and provide further support for the use of statins to confer additional cardioprotective benefits in older adults.

ABSTRACT

Attenuated reflex cutaneous vasodilatation in healthy human ageing is mediated by alterations in both central (sympathetic outflow) and peripheral (microvascular endothelial) function. Hypercholesterolaemia is associated with further impairments in neurovascular function. HMG-CoA reductase inhibitors (statins) improve cutaneous endothelium-dependent dilatation; however, whether statin therapy alters skin sympathetic nervous system activity (SSNA) or its relation to cutaneous vascular conductance (CVC) during passive heat stress is unknown. We hypothesized that (1) hypercholesterolaemic older adults would demonstrate blunted increases in both SSNA and CVC during passive heating and (2) chronic statin treatment would improve the response range and sensitivity of the SSNA:CVC relation. Reflex vasodilatation in response to a 1.0°C rise in oral temperature (T_or ; water perfused suit) was induced in 13 healthy normocholesterolaemic adults (62 ± 2 years; LDL = 113 ± 7 mg/dl), 10 hypercholesterolaemic adults (60 ± 1 years; LDL = 183 ± 2 mg/dl), and 10 previously hypercholesterolaemic adults (64 ± 1 years; LDL = 102 ± 2 mg/dl) treated with lipophilic statin (10-40 mg daily). SSNA (peroneal microneurography) and red cell flux (laser-Doppler flowmetry) in the innervated dermatome (dorsum of foot) were continuously measured. Reflex vasodilatation was blunted in hypercholesterolaemic adults, but not in statin-treated adults, compared to normocholesterolaemic adults (at ∆T_or  = 1.0°C: normal = 36 ± 1%CVC_max , high = 32 ± 1%CVC_max , statin = 38 ± 1%CVC_max ; P < 0.01). ∆SSNA was not different (at ∆T_or  = 1.0°C: normal: ∆ = 393 ± 96%, high: ∆ = 311 ± 120%, statin: ∆ = 256 ± 90%; P = 0.11). The slope of the SSNA:CVC relation was blunted in hypercholesterolaemic adults (0.02 ± 0.03%CVC_max /%_baseline ) compared to both normocholesterolaemic (0.09 ± 0.02%CVC_max /%_baseline ; P = 0.024) and statin-treated (0.12 ± 0.05%CVC_max /%_baseline ; P = 0.03) adults. Chronic statin treatment improves reflex cutaneous vasodilatation in formerly hypercholesterolaemic older adults by increasing end-organ responsiveness to sympathetic outflow during passive heat stress.

Effect of statins on the association between high temperature and all-cause mortality in a socioeconomically disadvantaged population: a cohort study

High temperature increases all-cause mortality. Thermoregulatory ability is impaired in persons with elevated serum cholesterol, but can be improved by the administration of statins, even in the short-term. We investigated whether the impact of high temperature (≥24 °C) on all-cause mortality among socioeconomically disadvantaged adults with a current or past indication for a statin is attenuated by current use of a statin with temperature dependence, by using claims data from five US Medicaid programs supplemented with Medicare claims for dual-enrollees and meteorological data from 1999-2010. We identified 3,508,948 persons (3,181,752 person-years) in a 1:1 propensity score-matched cohort. The incidence rate of all-cause mortality (deaths per 1,000 person-years) was 21.9 (95% confidence interval [CI]: 21.6 to 22.3) in current statin users and 30.1 (95% CI: 30.2 to 30.6) in former users. The adjusted odds ratios of mortality for current vs. former statin use were statistically significantly lower than 1.0, suggesting a protective effect of current statin use, on days with high temperature, with either daily average temperature or daily maximum temperature, and declined as daily average temperature increased from 29 °C and daily maximum temperature increased from 34 °C. These results were robust to the adjustment for daily relative humidity.

Attenuated cutaneous microvascular function in healthy young African Americans: Role of intradermal l-arginine supplementation

It has been established that endothelial function in conduit vessels is reduced in young African Americans (AA) relative to Caucasian Americans (CA). However, less is known regarding endothelial function in microvasculature of young AA. We hypothesized that microvascular function in response to local heating of skin is attenuated in young AA relative to age-matched CA due largely to the lack of NO bioavailability, which is in turn improved by intradermal l-arginine supplementation and/or inhibition of arginase. Nine AA and nine CA adults participated in this study. Participants were instrumented with four microdialysis membranes in the cutaneous vasculature of one forearm and were randomly assigned to receive 1) lactated Ringer's solution as a control site; 2) 20 mM NG-nitro-l-arginine (l-NAME) to inhibit NO synthase activity; 3) 10 mM l-arginine to local supplement l-arginine; or 4) a combination of 5.0 mM (S)-(2‑boronoethyl)-l-cysteine-HCL (BEC) and 5.0 mM Nω-hydroxy-nor-l-arginine (nor-NOHA) at a rate of 2.0 μl/min to locally inhibit arginase activity. Cutaneous vascular conductance (CVC) was calculated as red blood cell flux divided by mean arterial pressure. All CVC data were presented as a percentage of maximal CVC (%CVCmax) that was determined by maximal cutaneous vasodilation induced by 44 °C heating plus sodium nitroprusside administration. The response during the 42 °C local heating plateau was blunted in the AA at the control site (CA: 84 ± 12 vs. AA: 62 ± 6 vs. %CVCmax; P < 0.001). This response was improved in AA at the l-arginine site (Control: 62 ± 6 vs. l-arginine: 70 ± 18%CVCmax; P < 0.05) but not in the arginase inhibited site (Control: 62 ± 6 vs. Arginase inhibited: 62 ± 13%CVCmax; P = 0.91). In addition, the AA group had an attenuated NO contribution to the plateau phase during 42 °C local heating relative to the CA group (CA: 56 ± 14 vs. AA: 44 ± 6 Δ %CVCmax; P < 0.001). These findings suggest that 1) cutaneous microvascular function in response to local heating is blunted in young AA when compared to age-matched young CA; 2) this attenuated response is partly related to decrease in NO bioavailability in young AA; and 3) a local infusion of l-arginine, but not arginase inhibition, improves cutaneous microvascular responses to local heating in young AA relative to CA.

Fluid replacement modulates oxidative stress- but not nitric oxide-mediated cutaneous vasodilation and sweating during prolonged exercise in the heat

The roles of nitric oxide synthase (NOS), reactive oxygen species (ROS), and angiotensin II type 1 receptor (AT1R) activation in regulating cutaneous vasodilation and sweating during prolonged (≥60 min) exercise are currently unclear. Moreover, it remains to be determined whether fluid replacement (FR) modulates the above thermoeffector responses. To investigate, 11 young men completed 90 min of continuous moderate intensity (46% V̇o2peak) cycling performed at a fixed rate of metabolic heat production of 600 W (No FR condition). On a separate day, participants completed a second session of the same protocol while receiving FR to offset sweat losses (FR condition). Cutaneous vascular conductance (CVC) and local sweat rate (LSR) were measured at four intradermal microdialysis forearm sites perfused with: 1) lactated Ringer (Control); 2) 10 mM NG-nitro-l-arginine methyl ester (l-NAME, NOS inhibition); 3) 10 mM ascorbate (nonselective antioxidant); or 4) 4.34 nM losartan (AT1R inhibition). Relative to Control (71% CVCmax at both time points), CVC with ascorbate (80% and 83% CVCmax) was elevated at 60 and 90 min of exercise during FR (both P < 0.02) but not at any time during No FR (all P > 0.31). In both conditions, CVC was reduced at end exercise with l-NAME (60% CVCmax; both P < 0.02) but was not different relative to Control at the losartan site (76% CVCmax; both P > 0.19). LSR did not differ between sites in either condition (all P > 0.10). We conclude that NOS regulates cutaneous vasodilation, but not sweating, irrespective of FR, and that ROS influence cutaneous vasodilation during prolonged exercise with FR.

Edward F. Adolph Distinguished Lecture: Skin-deep insights into vascular aging

The skin is an accessible model circulation for studying vascular function and dysfunction across the lifespan. Age-related changes, as well as those associated with disease progression, often appear first in the cutaneous circulation. Furthermore, impaired vascular signaling and attendant endothelial dysfunction, the earliest indicators of cardiovascular pathogenesis, occur in a similar fashion across multiple tissue beds throughout the body, including the skin. Because microvascular dysfunction is a better predictor of long-term outcomes and adverse cardiovascular events than is large vessel disease, an understanding of age-associated changes in the control of the human cutaneous microcirculation is important. This review focuses on 1) the merits of using skin-specific methods and techniques to study vascular function, 2) microvascular changes in aged skin (in particular, the role of the endothelial-derived dilator nitric oxide), and 3) the impact of aging on heat-induced changes in skin vasodilation. While skin blood flow is controlled by multiple, often redundant, mechanisms, our laboratory has used a variety of distinct thermal provocations of this model circulation to isolate specific age-associated changes in vascular function. Skin-specific approaches and techniques, such as intradermal microdialysis coupled with laser-Doppler flowmetry (in vivo) and biochemical analyses of skin biopsy samples (in vitro), have allowed for the targeted pharmacodissection of the mechanistic pathways controlling skin vasoreactivity and study of the impact of aging and disease states. Aged skin has an attenuated ability to vasodilate in response to warm stimuli and to vasoconstrict in response to cold stimuli.

Endothelial function is impaired in the cutaneous microcirculation of adults with psoriasis through reductions in nitric oxide-dependent vasodilation

Psoriasis is an independent risk factor for cardiovascular disease; however, the underlying mechanisms are not fully understood. Deficits in conduit arterial function are evident in patients with psoriasis, but potential impairments in microcirculatory endothelial function remain unclear. We hypothesized that cutaneous microvascular dysfunction would be detectable in otherwise healthy individuals with psoriasis. Two intradermal microdialysis fibers were placed in (nonlesional) forearm skin of nine patients (3 men and 6 women, 39 ± 5 yr) with moderate (16 ± 2% of body surface area) plaque psoriasis and nine healthy (nonpsoriatic) control subjects (3 men and 6 women, 38 ± 5 yr) for local delivery of 1) lactated Ringer solution (control) and 2) 10 mM l-ascorbate (a nonspecific antioxidant). An index of skin blood flow was measured using laser-Doppler flowmetry during local heating (42°C). Nitric oxide (NO)-dependent vasodilation was directly quantified after perfusion of the nonspecific NO synthase inhibitor N^G-nitro-l-arginine methyl ester (15 mM). A third fiber was perfused with increasing concentrations (10^-10 - 10^-2 M) of norepinephrine to elicit adrenoreceptor-mediated cutaneous vasoconstriction. NO-dependent vasodilation was attenuated in patients with psoriasis (57 ± 5% and 39 ± 7% maximum cutaneous vascular conductance in control subjects and adults with psoriasis, respectively, P < 0.01). l-Ascorbate did not improve NO-dependent vasodilation ( P > 0.05). There was no group difference in maximal vasoconstriction or microvascular sensitivity to norepinephrine ( P > 0.05). These data suggest that NO bioavailability is reduced in otherwise healthy individuals with psoriasis, which contributes to systemic microvascular dysfunction. NEW & NOTEWORTHY In adults with psoriasis, reduced nitric oxide bioavailability mediates impaired endothelium-dependent vasodilation, independent of increases in oxidative stress. Furthermore, the degree of psoriatic symptomology is directly related to greater reductions in nitric oxide-dependent vasodilation.

Acute dairy milk ingestion does not improve nitric oxide-dependent vasodilation in the cutaneous microcirculation

In epidemiological studies, chronic dairy milk consumption is associated with improved vascular health and reduced age-related increases in blood pressure. Although milk protein supplementation augments conduit artery flow-mediated dilation, whether or not acute dairy milk intake may improve microvascular function remains unclear. We hypothesised that dairy milk would increase direct measurement of endothelial nitric oxide (NO)-dependent cutaneous vasodilation in response to local skin heating. Eleven men and women (61 (sem 2) years) ingested two or four servings (473 and 946 ml) of 1 % dairy milk or a rice beverage on each of 4 separate study days. In a subset of five subjects, an additional protocol was completed after 473 ml of water ingestion. Once a stable blood flow occurred, 15 mm-N G -nitro-l-arginine methyl ester was perfused (intradermal microdialysis) to quantify NO-dependent vasodilation. Red-blood-cell flux (RBF) was measured by laser-Doppler flowmetry, and cutaneous vascular conductance (CVC=RBF/mean arterial pressure) was calculated and normalised to maximum (%CVCmax; 28 mm-sodium nitroprusside). Full expression of cutaneous vasodilation was not different among dairy milk, rice beverage and water, and there was no effect of serving size on the total vasodilatory response. Contrary to our hypothesis, NO-dependent vasodilation was lower for dairy milk than rice beverage (D: 49 (sem 5), R: 55 (sem 5) %CVCmax; P<0·01). Acute dairy milk ingestion does not augment NO-dependent vasodilation in the cutaneous microcirculation compared with a rice beverage control.

Cutaneous vasodilator and vasoconstrictor mechanisms in temperature regulation

In this review, we focus on significant developments in our understanding of the mechanisms that control the cutaneous vasculature in humans, with emphasis on the literature of the last half-century. To provide a background for subsequent sections, we review methods of measurement and techniques of importance in elucidating control mechanisms for studying skin blood flow. In addition, the anatomy of the skin relevant to its thermoregulatory function is outlined. The mechanisms by which sympathetic nerves mediate cutaneous active vasodilation during whole body heating and cutaneous vasoconstriction during whole body cooling are reviewed, including discussions of mechanisms involving cotransmission, NO, and other effectors. Current concepts for the mechanisms that effect local cutaneous vascular responses to local skin warming and cooling are examined, including the roles of temperature sensitive afferent neurons as well as NO and other mediators. Factors that can modulate control mechanisms of the cutaneous vasculature, such as gender, aging, and clinical conditions, are discussed, as are nonthermoregulatory reflex modifiers of thermoregulatory cutaneous vascular responses.

Effect of vitamin C on endothelial function in health and disease: a systematic review and meta-analysis of randomised controlled trials

BACKGROUND

Observational studies indicate that higher vitamin C intake is associated with reduced risk for cardiovascular diseases. However, randomised controlled trials (RCT) examining the effect of vitamin C on endothelial function (EF) have reported inconsistent results. The aims of this systematic review and meta-analysis were to determine the effect of vitamin C supplementation on EF and to investigate whether the effect was influenced by health status, study duration, dose and route of vitamin C administration.

METHODS

We searched the Medline, Embase, Cochrane Library, and Scopus databases from inception to May 2013 for studies that met the following criteria: 1) RCT with adult participants, 2) vitamin C administered alone, 3) studies that quantified EF using commonly applied methods including ultrasound, plethysmography and pulse wave analysis.

RESULTS

Pooling the data from 44 clinical trials showed a significant positive effect of vitamin C on EF (SMD: 0.50, 95% CI: 0.34, 0.66, P < 0.001). Stratification of the analysis by health outcome revealed improved EF in atherosclerotic (SMD: 0.84, 95% CI: 0.41, 1.26, P < 0.001), diabetic (SMD: 0.52, 95% CI: 0.21, 0.82, P < 0.001) and heart failure patients (SMD: 0.48, 95% CI: 0.08, 0.88, P < 0.02) after vitamin C supplementation. The effect size appeared to be unaffected by study design, duration, baseline plasma vitamin C concentration or route of administration of vitamin C. The meta-regression showed a significant positive association between vitamin C dose and improvement in EF (β: 0.00011, 95% CI: 0.00001, 0.00021, P = 0.03).

CONCLUSIONS

Vitamin C supplementation improved EF. The effect of vitamin C supplementation appeared to be dependent on health status, with stronger effects in those at higher cardiovascular disease risk. PROSPERO Database registration: CRD42013004567, http://www.crd.york.ac.uk/prospero/

Altered skin flowmotion in hypertensive humans

Essential hypertensive humans exhibit attenuated cutaneous nitric oxide (NO)-dependent vasodilation. Using spectral analysis (fast Fourier transformation) we aimed to characterize the skin flowmotion contained in the laser-Doppler flowmetry recordings during local heating-induced vasodilation before and after concurrent pharmacological inhibition of nitric oxide synthase (NOS) in hypertensive and age-matched normotensive men and women. We hypothesized that hypertensive subjects would have lower total power spectral densities (PSDs), specifically in the frequency intervals associated with intrinsic endothelial and neurogenic control of the microvasculature. Furthermore, we hypothesized that NOS inhibition would attenuate the endothelial frequency interval. Laser-Doppler flowmetry recordings during local heating experiments from 18 hypertensive (MAP: 108±2mmHg) and 18 normotensive (MAP: 88±2mmHg) men and women were analyzed. Within site NO-dependent vasodilation was assessed by perfusion of a non-specific NOS inhibitor (N(G)-nitro-l-arginine methyl ester; l-NAME) through intradermal microdialysis during the heating-induced plateau in skin blood flow. Local heating-induced vasodilation increased total PSD for all frequency intervals (all p<0.001). Hypertensives had a lower total PSD (p=0.03) and absolute neurogenic frequency intervals (p<0.01) compared to the normotensives. When normalized as a percentage of total PSD, hypertensives had reduced neurogenic (p<0.001) and augmented myogenic contributions (p=0.04) to the total spectrum. NOS inhibition decreased total PSD (p<0.001) for both groups, but hypertensives exhibited lower absolute endothelial (p<0.01), neurogenic (p<0.05), and total PSD (p<0.001) frequency intervals compared to normotensives. These data suggest that essential hypertension results in altered neurogenic and NOS-dependent control of skin flowmotion and support the use of spectral analysis as a non-invasive technique to study vasoreactivity.

Nonuniform, age-related decrements in regional sweating and skin blood flow

Aging is associated with attenuated thermoregulatory function that varies regionally over the body. Decrements in vasodilation and sweating are well documented with age, yet limited data are available concerning the regional relation between these responses. We aimed to examine age-related alterations in the relation between regional sweating (RSR) and skin blood flow (SkBF) to thermal and pharmacological stimuli. Four microdialysis fibers were inserted in the ventral forearm, abdomen, thigh, and lower back of eight healthy aged subjects (64 ± 7 yr) and nine young (23 ± 3 yr) during 1) ACh dose response (1 × 10(-7) to 0.1 M, mean skin temperature 34°C) and 2) passive whole body heating to Δ1°C rise in oral temperature (Tor). RSR and SkBF were measured over each microdialysis membrane using ventilated capsules and laser-Doppler flowmetry. Maximal SkBF was measured at the end of both protocols (50 mM SNP). Regional sweating thresholds and RSR were attenuated in aged vs. young at all sites (P < 0.0001) during whole body heating. Vasodilation thresholds were similar between groups (P > 0.05). Attenuated SkBF were observed at the arm and back in the aged, representing 56 and 82% of those in the young at these sites, respectively (0.5 ΔTor). During ACh perfusion, SkBF (P = 0.137) and RSR were similar between groups (P = 0.326). Together these findings suggest regional age-related decrements in heat-activated sweat gland function but not cholinergic sensitivity. Functional consequences of such thermoregulatory impairment include the compromised ability of older individuals to defend core temperature during heat exposure and a subsequently greater susceptibility to heat-related illness and injury.

Oral clopidogrel improves cutaneous microvascular function through EDHF-dependent mechanisms in middle-aged humans

Platelet P₂Y₁₂-ADP and COX-1 receptor inhibition with oral clopidogrel (CLO) and low-dose aspirin (ASA), respectively, attenuates reflex-mediated cutaneous vasodilation, but little is known about how these medications affect local vasodilatory signaling. Reactive hyperemia (RH) results in vasodilation that is mediated by sensory nerves and endothelium-derived hyperpolarization factors (EDHF) through large-conductance calcium-activated potassium channels, whereas slow local heating (LH) elicits vasodilation largely through the production of nitric oxide (NO). We hypothesized that CLO and ASA would attenuate locally mediated cutaneous vasodilation assessed by RH and LH (0.5°C/min). In a randomized, cross-over, double-blind placebo-controlled study, nine healthy men and women (56 ± 1 yr) took CLO (75 mg), ASA (81 mg), and placebo for 7 days. Skin blood flow was measured (laser-Doppler flowmetry, LDF) and cutaneous vascular conductance (CVC) was calculated (LDF/mean arterial pressure) and normalized to maximal CVC (%CVCmax: 43°C and 28 mM sodium nitroprusside). RH response parameters, including area under the curve (AUC), total hyperemic response (THR), and the decay constant tau (λ) were calculated. NO-dependent vasodilation during LH was assessed by calculating the difference in %CVCmax between a control site and an NO synthase-inhibited site (10 mM l-NAME: intradermal microdialysis). CLO augmented the AUC and THR (AUCclo = 3,783 ± 342; THRclo = 2,306 ± 266% CVCmax/s) of the RH response compared with ASA (AUCASA = 3,101 ± 325; THRASA = 1,695 ± 197% CVCmax/s) and placebo (AUCPlacebo = 3,000 ± 283; THRPlacebo = 1,675 ± 170% CVCmax/s; all P < 0.0001 vs. CLO). There was no difference in the LH response or calculated NO-dependent vasodilation among treatments (all P > 0.05). Oral CLO treatment augments vasodilation during RH but not LH, suggesting that CLO may improve cutaneous microvascular function.

Tetrahydrobiopterin increases NO-dependent vasodilation in hypercholesterolemic human skin through eNOS-coupling mechanisms

Localized exogenous R-tetrahydrobiopterin (R-BH(4)) corrects the deficit in local heat-induced vasodilation (VD) in hypercholesterolemic (HC) human skin through one of two plausible mechanisms: by serving as an essential cofactor to stabilizing endothelial nitric oxide (NO) synthase (eNOS) or through generalized antioxidant effects. We used the stereoisomer S-BH(4), which has the same antioxidant properties but does not function as an essential NOS cofactor, to elucidate the mechanism by which R-BH(4) restores cutaneous VD in HC humans. Intradermal microdialysis fibers were placed in 20 normocholesterolemic (NC), 13 midrange cholesterolemic (MC), and 18 HC (LDL: 94 ± 3, 124 ± 3 and 179 ± 6 mg/dl, respectively) men and women to perfuse Ringer (control site) and R-BH(4). In 10 NC, 13 MC, and 9 HC subjects (LDL: 94 ± 3, 124 ± 3, 180 ± 10 mg/dl), S-BH(4) was perfused at a third microdialysis site. Skin blood flow was measured during a standardized local heating protocol to elicit eNOS-dependent VD. After cutaneous vascular conductance (CVC = LDF/MAP) plateaued, NO-dependent VD was quantified by perfusing N(G)-nitro-l-arginine methyl ester (l-NAME). Data were normalized as %CVC(max). Fully expressed VD (NC: 97.9 ± 2.3 vs. MC: 85.4 ± 5.4, HC: 79.9 ± 4.2%CVC(max)) and the NO-dependent portion (NC: 62.1 ± 3 vs. MC: 45.8 ± 3.9, HC: 35.7 ± 2.8%CVC(max)) were reduced in HC (both P < 0.01 vs. NC), but only the fully expressed VD was reduced in MC (P < 0.01 vs. NC). R-BH(4) increased the fully expressed (93.9 ± 3.4%CVC(max); P < 0.01) and NO-dependent VD (52.1 ± 5.1%CVC(max); P < 0.01) in HC but not in NC or MC. S-BH(4) increased full-expressed VD in HC (P < 0.01) but did not affect NO-dependent VD in HC or MC. In contrast S-BH(4) attenuated NO-dependent VD in NC (control: 62.1 ± 3 vs. S-BH(4): 41.6 ± 7%CVC(max); P < 0.001). Exogenous R-BH(4) restores NO-dependent VD in HC human skin predominantly through NOS coupling mechanisms but increases full expression of the local heating response through generalized antioxidant properties.

Cutaneous microvascular dysfunction correlates with serum LDL and sLOX-1 receptor concentrations

The human cutaneous circulation is an accessible and representative regional circulation for investigating mechanisms of microvascular dysfunction, a systemic disease process occurring early in the pathogenesis of atherosclerosis. Elevated concentrations of low-density lipoproteins ([LDL]) are highly atherogenic and independently associated with the severity of coronary atherosclerosis through their actions on the lectin-like oxidized LDL receptors (LOX-1). We hypothesized that cutaneous microvascular dysfunction, as measured by a decrement in endothelial nitric oxide- (NO-) dependent vasodilation during local heating, would be correlated with serum [LDL], oxidized [LDL], and soluble LOX-1 receptors [sLOX-1]. Intradermal microdialysis fibers were placed in the skin of 53 otherwise healthy men and women (aged 52±8 years) whose serum [LDL] ranged from 72 to 233 mg/dL. Skin blood flow was measured by laser Doppler flowmetry over a local forearm skin site as it was heated (42°C) to induce sustained local vasodilation. After flux plateaued, L-NAME was infused to block endothelial NO synthase in order to determine the NO-dependent portion of the vasodilatory response. Data were normalized to maximal cutaneous vascular conductance (CVC). NO-dependent vasodilation was reduced as a linear function of [LDL] (R(2)=0.303, p<0.001), oxidized [LDL] (R(2)=0.214, p<0.001), and [sLOX-1] (R(2)=0.259, p=0.026) but was unrelated to high-density lipoprotein (HDL) concentration (R(2)=0.003, p=0.68). Hypercholesterolemia-induced microvascular dysfunction is related to various LDL markers and involves a reduction in NO-dependent vasodilation that appears to be a progressive process measurable in the skin microcirculation.

Endothelial nitric oxide synthase mediates cutaneous vasodilation during local heating and is attenuated in middle-aged human skin

Local skin heating is used to assess microvascular function in clinical populations because NO is required for full expression of the response; however, controversy exists as to the precise NO synthase (NOS) isoform producing NO. Human aging is associated with attenuated cutaneous vasodilation but little is known about the middle aged, an age cohort used for comparison with clinical populations. We hypothesized that endothelial NOS (eNOS) is the primary isoform mediating NO production during local heating, and eNOS-dependent vasodilation would be reduced in middle-aged skin. Vasodilation was induced by local heating (42°C) and during acetylcholine dose-response (ACh-DR: 0.01, 0.1, 1.0, 5.0, 10.0, 50.0, 100.0 mmol/l) protocols. Four microdialysis fibers were placed in the skin of 24 men and women; age cohorts were 12 middle-aged (53 ± 1 yr) and 12 young (23 ± 1 yr). Sites served as control, nonselective NOS inhibited [N(G)-nitro-l-arginine methyl ester (l-NAME)], inducible NOS (iNOS) inhibited (1400W), and neuronal NOS (nNOS) inhibited (N(ω)-propyl-l-arginine). After full expression of the local heating response, l-NAME was perfused at all sites. Cutaneous vascular conductance was measured and normalized to maximum (%CVC(max): Nitropress). l-NAME reduced %CVCmax at baseline, all phases of the local heating response, and at all ACh concentrations compared with all other sites. iNOS inhibition reduced the initial peak (53 ± 2 vs. 60 ± 2%CVC(max); P < 0.001); however, there were no other differences between control, nNOS-, and iNOS-inhibited sites during the phases of local heating or ACh-DR. When age cohorts were compared, NO-dependent vasodilation during local heating (52 ± 6 vs. 68 ± 4%CVC(max); P = 0.013) and ACh perfusion (50 mmol/l: 83 ± 3 vs. 93 ± 2%CVC(max); 100 mmol/l: 83 ± 4 vs. 92 ± 3%CVC(max); both P = 0.03) were reduced in middle-aged skin. There were no differences in NOS isoform expression obtained from skin biopsy samples between groups (all P > 0.05). These data suggest that eNOS mediates the production of NO during local heating and that cutaneous vasodilation is attenuated in middle-aged skin.

Local tetrahydrobiopterin administration augments reflex cutaneous vasodilation through nitric oxide-dependent mechanisms in aged human skin

Functional constitutive nitric oxide synthase (NOS) is required for full expression of reflex cutaneous vasodilation that is attenuated in aged skin. Both the essential cofactor tetrahydrobiopterin (BH(4)) and adequate substrate concentrations are necessary for the functional synthesis of nitric oxide (NO) through NOS, both of which are reduced in aged vasculature through increased oxidant stress and upregulated arginase, respectively. We hypothesized that acute local BH(4) administration or arginase inhibition would similarly augment reflex vasodilation in aged skin during passive whole body heat stress. Four intradermal microdialysis fibers were placed in the forearm skin of 11 young (22 ± 1 yr) and 11 older (73 ± 2 yr) men and women for local infusion of 1) lactated Ringer, 2) 10 mM BH(4), 3) 5 mM (S)-(2-boronoethyl)-l-cysteine + 5 mM N(ω)-hydroxy-nor-l-arginine to inhibit arginase, and 4) 20 mM N(G)-nitro-l-arginine methyl ester (l-NAME) to inhibit NOS. Red cell flux was measured at each site by laser-Doppler flowmetry (LDF) as reflex vasodilation was induced. After a 1.0°C rise in oral temperature (T(or)), mean body temperature was clamped and 20 mM l-NAME was perfused at each site. Cutaneous vascular conductance was calculated (CVC = LDF/mean arterial pressure) and expressed as a percentage of maximum (%CVC(max); 28 mM sodium nitroprusside and local heat, 43°C). Vasodilation was attenuated at the control site of the older subjects compared with young beginning at a 0.3°C rise in T(or). BH(4) and arginase inhibition both increased vasodilation in older (BH(4): 55 ± 5%; arginase-inhibited: 47 ± 5% vs. control: 37 ± 3%, both P < 0.01) but not young subjects compared with control (BH(4): 51 ± 4%CVC(max); arginase-inhibited: 55 ± 4%CVC(max) vs. control: 56 ± 6%CVC(max), both P > 0.05) at a 1°C rise in T(or). With a 1°C rise in T(or), local BH(4) increased NO-dependent vasodilation in the older (BH(4): 31.8 ± 2.4%CVC(max) vs. control: 11.7 ± 2.0%CVC(max), P < 0.001) but not the young (BH(4): 23 ± 4%CVC(max) vs. control: 21 ± 4%CVC(max), P = 0.718) subject group. Together these data suggest that reduced BH(4) contributes to attenuated vasodilation in aged human skin and that BH(4) NOS coupling mechanisms may be a potential therapeutic target for increasing skin blood flow during hyperthermia in older humans.

Acute localized administration of tetrahydrobiopterin and chronic systemic atorvastatin treatment restore cutaneous microvascular function in hypercholesterolaemic humans

Elevated oxidized low-density lipoproteins (LDL) are associated with vascular dysfunction in the cutaneous microvasculature, induced in part by upregulated arginase activity and increased globalized oxidant stress. Since tetrahydrobiopterin (BH(4)) is an essential cofactor for endothelial nitric oxide synthase (NOS3), decreased bioavailability of the substrate l-arginine and/or BH(4) may contribute to decreased NO production with hypercholesterolaemia. We hypothesized that (1) localized administration of BH(4) would augment NO-dependent vasodilatation in hypercholesterolaemic human skin, which would be further increased when combined with arginase inhibition and (2) the improvement induced by localized BH(4) would be attenuated after a 3 month oral atorvastatin intervention (10 mg). Four microdialysis fibres were placed in the skin of nine normocholesterolaemic (NC: LDL = 95 ± 4 mg dl(-1)) and nine hypercholesterolaemic (HC: LDL = 177 ± 6 mg dl(-1)) men and women before and after 3 months of systemic atorvastatin. Sites served as control, NOS inhibited, BH(4), and arginase inhibited + BH(4) (combo). Skin blood flow was measured while local skin heating (42°C) induced NO-dependent vasodilatation. After the established plateau l-NAME was perfused in all sites to quantify NO-dependent vasodilatation (NO). Data were normalized to maximum cutaneous vascular conductance (CVC). Vasodilatation at the plateau and NO-dependent vasodilatation were reduced in HC subjects (plateau HC: 70 ± 5% CVC(max) vs. NC: 95 ± 2% CVC(max); NO HC: 45 ± 5% CVC(max) vs. NC: 64 ± 5% CVC(max); both P < 0.001). Localized BH(4) alone or combo augmented the plateau (BH(4): 93 ± 3% CVC(max); combo 89 ± 3% CVC(max), both P < 0.001) and NO-dependent vasodilatation in HC (BH(4): 74 ± 3% CVC(max); combo 76 ± 3% CVC(max), both P < 0.001), but there was no effect in NC subjects (plateau BH(4): 90 ± 2% CVC(max); combo 95 ± 3% CVC(max); NO-dependent vasodilatation BH(4): 68 ± 3% CVC(max); combo 58 ± 4% CVC(max), all P > 0.05 vs. control site). After the atorvastatin intervention (LDL = 98 ± mg * dl(-1)) there was an increase in the plateau in HC (96 ± 4% CVC(max), P < 0.001) and NO-dependent vasodilatation (68 ± 3% CVC(max), P < 0.001). Localized BH(4) alone or combo was less effective at increasing NO-dependent vasodilatation after the drug intervention (BH(4): 60 ± 5% CVC(max); combo 58 ± 2% CVC(max), both P < 0.001). These data suggest that decreased BH(4) bioavailability contributes in part to cutaneous microvascular dysfunction in hypercholesterolaemic humans and that atorvastatin is an effective systemic treatment for improving NOS coupling mechanisms in the microvasculature.