Cutaneous Microvascular Responses Research Articles

Divergent Vasodilator Mechanisms to Endothelial-Dependent Agonists with Advancing Age

Introduction: Microvascular function is maintained by a number of vasodilating factors, with nitric oxide (NO) and endothelial hyperpolarizing factors (EDHF) predominating. Advancing age is an independent risk factor in the development of cardiovascular disease, and NO-mediated vasodilation declines, or is unchanged, depending on the vascular bed examined, number of cardiovascular risk factors, or specific endothelial-dependent agonist used. Mechanisms contributing to cutaneous microvascular dysfunction with age have been attributed largely to reductions in NO signaling, but the role of EDHF-mediated dilation, particularly to acetylcholine (ACh), remains unclear. The purpose of this study was to determine the endothelial mechanisms contributing to age-induced cutaneous microvascular function and compare cutaneous microvascular function responses to those from isolated adipose arteriole preparations. We hypothesized that cutaneous microvascular vasodilation to ACh in older adults will be mediated primarily by EDHFs relative to young adults and that isolated adipose arteriole preparations will corroborate these findings. Methods: Four intradermal microdialysis fibers were placed in the skin of the ventral forearm of 9 young (3F/6M; 29±7 yrs) and 3 older adults (3F/0M; 59±11 yrs) for infusion of Ringer’s solution; L-NAME (10 mM), an NO synthase inhibitor; tetraethylammonium chloride (TEA; 50 mM), a non-specific K+ channel inhibitor; and a combination of L-NAME and TEA. Laser Doppler flowmetry and brachial mean arterial pressure were measured during infusion of ACh (10 mM and 100 mM) and in response to local heating to 39°C. Maximal vasodilation was assessed with heating to 43°C and infusion of sodium nitroprusside (28 mM). Adipose resistance arterioles for pressure myography were obtained from a gluteal biopsy or from surgical discard tissue, which were pre-constricted (ET-1), and ACh responses (10−9–10−4 M) were assessed in the presence of the above inhibitors. Cutaneous vascular conductance (CVC) and isolated arteriole responses are presented as % maximum vasodilation. Results: In response to local heating in young adults, L-NAME reduced vasodilator magnitude (Ringers 69.0±18.1% vs. L-NAME 30.3±12.1%; p< 0.05) while TEA did not have any effect (69±18% vs. 49±28%; p=0.20). Combined L-NAME and TEA reduced vasodilation (69±18% vs. 19±6%; p<0.05). Conversely, vasodilator magnitude to ACh was not different across the Ringers, L-NAME, or TEA sites (p=0.93-0.94), while combined inhibition of NOS and K+ channels with L-NAME and TEA, respectively, reduced vasodilator responsiveness (p<0.05). In isolated resistance arterioles, there were no differences in %max dilation to ACh across inhibitor sites (p=0.19) in young adults. In older adults, neither independent nor combined inhibition of NOS or K+ channels impacted vasodilator responses to local heating, while vasodilator magnitude to ACh was most impacted by combined inhibition with L-NAME and TEA (83±14% vs. 32±15%; p<0.05). Conclusion: Our data demonstrate that vasodilator plasticity in response to local heating is divergent with advancing age, relying on non-NO or K+ mechanisms relative to young adults, while NO and K+ mechanisms are suffcient to maintain ACh-mediated vasodilation. These findings further support the concept of diversity in vasodilator mechanisms within the microvasculature. NHLBI K99-HL161491 (WEH), K08-HL150340 (JJM), R01-HL160752 (JKF), R01-HL133029 (AB), and NICHD R01-HD099340 (MJD). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Acute impact of aerobic exercise on local cutaneous thermal hyperaemia.

Little is known about the acute changes in cutaneous microvascular function that occur in response to exercise, the accumulation of which may provide the basis for beneficial chronic cutaneous vascular adaptations. Therefore, we examined the effects of acute exercise on cutaneous thermal hyperaemia. Twelve healthy, recreationally active participants (11 male, 1 female) performed 30-minute cycling at 50% (low-intensity exercise, LOW) or 75% (high-intensity exercise, HIGH) maximum heart rate. Laser Doppler flowmetry (LDF) and rapid local skin heating were used to quantify cutaneous thermal hyperaemia before (PRE), immediately following (IMM) and 1-h (1HR) after exercise. Baseline, axon reflex peak, axon reflex nadir, plateau, maximum skin blood flow responses to rapid local heating (42°C for 30-min followed by 44°C for 15-min) at each stage were assessed and indexed as cutaneous vascular conductance [CVC=flux/mean arterial blood pressure (MAP), PU·mmHg-1], and expressed as a percentage of maximum (%CVCmax). Exercise increased heart rate (HR), MAP and skin blood flow (all P<0.001), and to a greater extent during HIGH (all P<0.001). The axon reflex peak and nadir were increased immediately and 1-h after exercise (all comparisons P<0.01 vs. PRE), which did not differ between intensities (peak: P=0.34, axon reflex nadir: P=0.91). The endothelium-dependent plateau response was slightly elevated after exercise (P=0.06), with no effect of intensity (P=0.58) nor any interaction effect (P=0.55). CONCLUSION: Exercise increases cutaneous microvascular axonal responses to local heating for up to 1-h, suggesting an augmented sensory afferent function post-exercise. Acute exercise may only modestly affect endothelial function in cutaneous microcirculation.

Effects of sensory nerve blockade on cutaneous microvascular responses to ischemia-reperfusion injury.

Examine the effects of sensory nerve blockade on cutaneous post-occlusive reactive hyperemia (PORH) and local thermal hyperemia (LTH) following prolonged upper limb ischemia. In nine males [28years (standard deviation:6)], volar forearm skin blood flux normalized to maximum vasodilation (%SkBFmax) was assessed at control (CTRL) and sensory nerve blockade (EMLA) treated sites during the PORH response following 20-min of complete arm ischemia and during rapid LTH (33-42°C, 1°C·20s-1, held for ~30-min+20-min at 44°C) before and after ischemia-reperfusion (IR) injury. EMLA increased mean [95% confidence-interval] PORH amplitude by 21%SkBFmax ([9,33]; p=0.003), delayed time to peak by 111s ([40,182]; p=0.007) and increased area under the curve by 19,462%SkBFmax·s ([11,346,27,579]; p<0.001) compared to CTRL. For LTH, EMLA delayed onset time by 76s ([46,106]; p<0.001) Pre-IR and by 46s ([27,65]; p<0.001) Post-IR compared to CTRL. Post-IR onset time was delayed for CTRL by 26s ([8,43]; p=0.007), but was not different for EMLA (p>0.050) compared to Pre-IR. EMLA delayed time to initial peak by 24s ([4,43]; p=0.022, Main time effect) and it attenuated the initial peak by 27%SkBFmax ([12,43]; p=0.002) Pre-IR and by 16%SkBFmax ([3,29]; p=0.020) post-IR compared to CTRL. Post-IR, the initial peak was not different for CTRL (p>0.050), but it was increased by 16%SkBFmax ([5,26]; p=0.005) for EMLA compared to Pre-IR. Neither EMLA nor IR altered the steady-state heating plateau (all p>0.050). For the current model of IR injury, sensory nerves appear to have a negligible influence on the LTH response in non-glabrous forearm skin once vasodilation has been initiated.

Two Weeks Of Remote Ischemic Preconditioning Improved Cutaneous Microvascular Responses To Post-occlusive Reactive Hyperemia

PURPOSE: Repeated remote ischemic preconditioning (RIPC), induced by intermittent periods of ischemia and reperfusion in a limb body, improves non-nitric oxide (NO)-mediated endothelial-dependent cutaneous vasodilation. Post-occlusive reactive hyperemia (PORH) occurs following the release of a brief arterial occlusion and is principally mediated by non-NO mediated vasodilatory factors such as prostaglandins, sensory nerve axon reflex, and endothelium-derived hyperpolarizing factors (EDHFs). However, the role of repeated bouts of RIPC on the PORH response is unknown. The purpose of this study was to test whether two weeks of RIPC improves PORH elicited cutaneous microvascular hyperemia responses. METHODS: The study was conducted with twenty-one participants (Control; 24 ± 5 yr old, 4 M/4F, n = 8, RIPC; 22 ± 2 yr old, 7 M/6F, n = 13). The RIPC group received RIPC daily sessions over a two-week period (3 intervals of 4 days with RIPC followed by a 1 day break). Each RIPC session consisted of 4 repetitions of 5-minute arm blood flow occlusion interspersed by 5-minute reperfusion. PORH was elicited by brachial artery occlusion for 5 minutes by inflating an arm cuff to 200 mmHg, and the cutaneous hyperemic response was measured after cuff release. Skin blood flow measurements were collected with laser speckle contrast image (LSCI) before and after the repeated RIPC intervention. The control group did not receive RIPC but underwent repeated PORH measurements two weeks later. RESULTS: Both Time to Peak (Tp) and max/time improved after two weeks of RIPC (Tp; 16.5 ± 2.1 vs.15.2 ± 2.9 s, Pre vs. Post, p < 0.05, max/time; 0.11 ± 0.03 vs. 0.13 ± 0.04 CVC/s, Pre vs. Post, p < 0.05). The control group did not change after 2 weeks. CONCLUSIONS: These data suggest that non-NO mediated vasodilator responses in the skin microvasculature may be affected with 2 weeks of repeated RIPC.

Effect of Short‐Term Estradiol Exposure on Endothelin‐B Receptor‐Mediated Vasodilation in Postmenopausal Women

Endothelin (ET)‐1 contributes to endothelial dysfunction in postmenopausal women (PMW) via the ETB receptor. We have previously shown that the ETB receptor mediates vasodilation in young women, an effect that is lost in PMW. However, it is unclear if ETB receptor‐mediated dilation can be restored in PMW exposed to E2.PURPOSETo test the hypothesis that E2 exposure restores ETB receptor‐mediated vasodilation in PMW.METHODSWe tested 9 PMW (55±2 yrs, 24±3 kg/m2, 91±5 mmHg) who self‐reported natural menopause and were at least 1 year without menses. We measured vasodilation in the cutaneous microcirculation via local heating using laser Doppler flowmetry coupled with intradermal microdialysis during perfusions of lactated Ringer’s (control), ETB receptor antagonist (BQ‐788, 300nM) and ETA receptor antagonist (BQ‐123, 500nM). Cutaneous vascular conductance (CVC) was calculated during the plateau phase of local heating (42°C), and normalized to maximal vasodilation achieved by perfusion of sodium nitroprusside (28mM) and heating to 43°C. All women were tested at baseline (BL) and after 7 days of E2 (Vivelle‐Dot, 0.1mg/day, transdermal patch) administration (+E2). A two‐way repeated measures ANOVA was performed to compare %CVCmax in PMW before and after E2 exposure. Data presented are mean ± standard deviation.RESULTSE2 administration increased serum estradiol (BL: 45±29 vs +E2: 71±42 pg/mL, P&lt;0.01) and reduced follicle stimulating hormone (BL: 71±13 vs +E2: 57±17 pg/mL, P&lt;0.01), but there were no changes in serum progesterone (BL: 0.57±0.93 vs +E2: 0.53±0.88 pg/mL, P=0.14) nor plasma ET‐1 (BL: 1.62±0.66 vs +E2: 1.54±0.54 pg/mL, P=0.42). E2 administration had no effect on cutaneous microvascular responses (Time P=0.41, Drug P=0.17, Interaction P=0.71). At BL, vasodilatory responses to local heating were not different during control and ETB receptor antagonism (control: 83±8 vs. BQ‐788: 88±6 %CVCmax). Similarly, vasodilation was not altered at BL during ETA receptor antagonism in a subset of women (n=6, control: 83±8 vs. BQ‐123: 87±8 %CVCmax). E2 administration did not improve vasodilation in the control site (BL: 83±8 vs. +E2 85±13 %CVCmax). Furthermore, there was no effect of E2 exposure on cutaneous vasodilatory responses during perfusion of ETB (BL: 88±6 vs. +E2: 89±6 %CVCmax) nor ETA (n=6, BL: 87±8 vs +E2: 92±7 %CVCmax) receptor antagonists.CONCLUSIONThese preliminary data suggest that short‐term E2 exposure does not modulate ETB receptor function in PMW. These findings are in contrast to our observations in young women demonstrating that ETB receptors mediate vasodilation in the presence of E2. The role of alternative therapies to modulate ETB receptor function should be considered in future studies.

Cutaneous Microvascular Responses to Local Heating on Ventral and Dorsal Aspects of the Forearm

The cutaneous microvasculature is considered a representative vascular bed and is regularly used to interrogate the mechanisms of microvascular function in healthy and diseased humans. For instance, cutaneous dilation in response to local heating can provide an index of nitric oxide (NO) bioavailability. While the skin of the forearm is typically used for local heating studies, some studies have used the ventral forearm while others have used the dorsal forearm skin for this assessment. Since the dorsal aspect of the forearm typically has more hair and receives greater sun exposure than the ventral side, there is speculation that cutaneous dilation may differ from one side of the forearm to the other, in magnitude and/or mechanism. As such, studies utilizing different sides of the forearm may not be comparable. Therefore, we aimed to test the hypothesis that cutaneous local heating responses differ between the ventral and dorsal aspects of the forearm in response to the two most common temperature stimuli, 39°C and 42°C.MethodsTen young, normotensive individuals (6 men/4 women, age: 26 ± 2 years) were studied on two separate occasions separated by 2‐7 days. At each visit, 4 intradermal microdialysis fibers were placed in either the ventral or dorsal forearm, in a random order. Two fibers were perfused with Ringer’s solution to serve as control sites and the other 2 fibers were perfused with 10 mM N(G)‐Nitro‐L‐arginine methyl ester (L‐NAME) to inhibit NO synthase. Red blood cell flux (RBCF) was assessed at all sites via laser Doppler flowmetry. Each pair of sites (control and L‐NAME) was heated to either 39°C or 42°C for ~40‐45 min until RBCF plateaued. All sites were then infused with 28 mM sodium nitroprusside and heated to 43°C to establish maximal RBCF. Cutaneous vascular conductance (CVC) was calculated as RBCF / mean arterial pressure measured during the plateau and maximal phases. Plateau results are reported as a percentage of maximal CVC at each respective site. The relative NO contribution is reported as: [(control plateau – L‐NAME plateau)/control plateau] x 100.ResultsNo differences were observed at the control site between ventral and dorsal aspects of the forearm when heated to 39°C (62 ± 13 vs. 62 ± 16 % CVCmax, P=0.99). Likewise, the heating response to 42°C was similar across the forearm (ventral: 90 ± 9 vs. dorsal: 86 ± 12% CVCmax, P=0.21). The relative contribution of NO to the plateau was comparable across the forearm at 39°C (ventral: 70 ± 20 vs. dorsal: 66 ± 21%, P=0.71) and 42°C (ventral: 63 ± 16 vs. dorsal: 69 ± 11%, P=0.11).DiscussionThese preliminary findings suggest that cutaneous vasodilation elicited by local heating is similar on both sides of the forearm at both 39°C and 42 °C. Additionally, it appears that the relative contribution of NO to local heating‐induced microvascular vasodilation is not different across the forearm.

Delayed Cutaneous Microvascular Responses With Non-consecutive 3 Days of Remote Ischemic Preconditioning.

The optimal frequency and duration of remote ischemic preconditioning (RIPC) that augments microvascular function is unknown. A single bout of RIPC increases cutaneous endothelial function for ∼48 h, whereas 1 week of daily RIPC bouts improves more sustained endothelium-independent function. We hypothesized that 3 days of RIPC separated by rest days (3QOD RIPC) would result in sustained increases in both endothelium-dependent and endothelium-independent functions. Cutaneous microvascular function was assessed in 13 healthy young participants (aged 20.5 ± 3.9 years; 5 males, 8 females) before 3QOD and then 24, 48, and 72 h and a week after 3QOD. RIPC consisted of four repetitions of 5 min of blood flow occlusion separated by 5 min of reperfusion. Skin blood flow responses to local heating (Tloc = 42°C), acetylcholine (Ach), and sodium nitroprusside (SNP) were measured using laser speckle contrast imaging and expressed as cutaneous vascular conductance (CVC = PU⋅mmHg–1). Local heating-mediated vasodilation was increased 72 h after 3QOD and the increased responsivity persisted a week later (1.08 ± 0.24 vs. 1.34 ± 0.46, 1.21 ± 0.36 PU⋅mmHg–1; ΔCVC, pre-RIPC vs. 72 h, a week after 3QOD; P = 0.054). Ach-induced cutaneous vasodilation increased a week after 3QOD (0.73 ± 0.41 vs. 0.95 ± 0.49 PU⋅mmHg–1; ΔCVC, pre-RIPC vs. a week after 3QOD; P < 0.05). SNP-induced cutaneous vasodilation increased 24 h after 3QOD (0.47 ± 0.28 vs. 0.63 ± 0.35 PU⋅mmHg–1; ΔCVC, pre-RIPC vs. 24 h; P < 0.05), but this change did not persist thereafter. Thus, 3QOD induced sustained improvement in endothelium-dependent vasodilation but was not sufficient to sustain increases in endothelium-independent vasodilation.

Cutaneous iontophoresis of vasoactive medications in patients with scleroderma-associated pulmonary arterial hypertension.

It remains unknown whether the cutaneous microvascular responses are different between patients with scleroderma-associated pulmonary arterial hypertension (SSc-PAH) and SSc without pulmonary hypertension (PH). We included 59 patients with SSc between March 2013 and September 2019. We divided patients into 4groups: (a) no PH by right heart catheterization (RHC) (n=8), (b) no PH by noninvasive screening tests (n=16), (c) treatment naïve PAH (n=16), and (d) PAH under treatment (n=19). Microvascular studies using laser Doppler flowmetry (LDF) were done immediately after RHC or at the time of an outpatient clinic visit (group b). The median (IQR) age was 59 (54-68) years, and 90% were females. The responses to local thermal stimulation and postocclusive reactive hyperemia, acetylcholine, and sodium nitroprusside iontophoresis were similar among groups. The microvascular response to treprostinil was more pronounced in SSc patients without PH by screening tests (% change: 340 (214-781)) compared with SSc-PAH (naïve+treatment) (Perfusion Units (PU) % change: 153 (94-255) % [p=.01]). The response to A-350619 (a soluble guanylate cyclase (sGC) activator) was significantly higher in patients with SSc without PH by screening tests (PU % change: 168 (46-1,296)) than those with SSc-PAH (PU % change: 22 (15-57) % [p=.006]). The % change in PU with A350619 was directly associated with cardiac index and stroke volume index (R: 0.36, p=.03 and 0.39, p=.02, respectively). Patients with SSc-PAH have a lower cutaneous microvascular response to a prostacyclin analog treprostinil and the sGC activator A-350619 when compared with patients with SSc and no evidence of PH on screening tests, presumably due to a peripheral reduction in prostacyclin receptor expression and nitric oxide bioavailability.

Cutaneous microvascular vasodilatory consequences of acute consumption of a caffeinated soft drink sweetened with high-fructose corn syrup.

This study tested the hypotheses that compared to drinking water, consumption of a caffeinated soft drink sweetened with high‐fructose corn syrup (HFCS) attenuates the cutaneous vasodilatory response to local skin heating without (Protocol 1) and following ischemia‐reperfusion injury (Protocol 2). In a randomized, counterbalanced crossover design, 14 healthy adults (25 ± 3 year, 6 women) consumed 500 ml of water (water) or a caffeinated soft drink sweetened with HFCS (Mtn. Dew, DEW). Thirty minutes following beverage consumption local skin heating commenced on the right forearm (Protocol 1), while on the left forearm ischemia‐reperfusion commenced with 20 min of ischemia followed by 20 min of reperfusion and then local skin heating (Protocol 2). Local skin heating involved 40 min of heating to 39℃ followed by 20 min of heating to 44℃. Skin blood flow (SkBf, laser Doppler) data were normalized to mean arterial pressure and are presented as a cutaneous vascular conductance (CVC) and as percentage of the CVC response during heating to 44℃ (%CVCmax). Protocol 1: During local heating at 39℃, no differences were observed in CVC (water: 2.0 ± 0.6 PU/mmHg; DEW: 2.0 ± 0.8 PU/mmHg, p = 0.83) or %CVCmax (water: 59 ± 14%; DEW 60 ± 15%, p = 0.84) between trials. Protocol 2: During local skin heating at 39℃, no differences were observed in CVC (water: 1.7 ± 0.5 PU/mmHg; DEW: 1.5 ± 0.5 PU/mmHg, p = 0.33) or %CVCmax (water: 64 ± 15%; DEW 61 ± 15% p = 0.62) between trials. The cutaneous microvascular vasodilator response to local heating with or without prior ischemia‐reperfusion injury is not affected by acute consumption of a caffeinated soft drink sweetened with HFCS.

Acute Consumption of a Caffeinated Soft Drink Sweetened with High Fructose Corn Syrup Does Not Modify the Cutaneous Microvascular Response to Ischemia‐Reperfusion Injury

Background Copious intake of soft drinks sweetened with high fructose corn syrup (HFCS) is associated with a heightened risk of cardiovascular disease, which is likely contributed to by chronic HFCS mediated endothelial dysfunction occurring secondary to decreased nitric oxide (NO) bioactivity. Acute consumption of a soft drink sweetened with HFCS does not affect cutaneous vasodilation during local heating, a functional test of NO bioactivity in the cutaneous microvasculature. However, this study was undertaken in the absence of a basal reduction in NO bioactivity, such as is speculated to occur with chronic intake of HFCS. Therefore, the present study tested the hypothesis that the cutaneous vasodilatory response to local skin heating following ischemia-reperfusion injury, which acutely reduces NO bioactivity, is attenuated following acute consumption of a caffeinated soft drink sweetened with HFCS compared to water. Methods In a randomized, counter-balanced crossover design, fourteen healthy young adults (six women) consumed 500 mL of either tap water (H2O) or a caffeinated soft drink sweetened with HFCS (Mtn. Dew®, DEW). 30 min following consumption, participants underwent 20 min of forearm ischemia and 20 min of reperfusion. Local skin heating at the forearm to 39⁰C was performed for 40 min and increased to 44⁰C for 20 min. Skin blood flow (SkBF) was measured on the dorsal forearm using laser Doppler flowmetry, blood pressure was measured using the Penaz method, and heart rate was measured via 3-lead electrocardiogram. Cutaneous vascular conductance (CVC) was calculated as the quotient of SkBF and mean arterial pressure (MAP). SkBF and CVC data during local heating to 39⁰C, which is mostly a NO mediated response, were normalized as a percentage of maximal values obtained during local skin heating to 44⁰C. Data are presented as mean ± SD. Results During local skin heating at 44⁰C, there were no differences observed between H20 and DEW trials for SkBF (H2O: 252 ± 37 PU; DEW: 240 ± 35 PU, p = 0.317), CVC (H2O: 2.6 ± 0.4 PU/mmHg; DEW: 2.4 ± 0.5 PU/mmHg, p =0.215), MAP (H2O: 96 ± 6 mmHg; DEW: 101 ± 10 mmHg, p = 0 .162), and heart rate (H2O: 59 ± 7 bpm; DEW 60 ± 10 bpm, p = 0.654). During local skin heating to 39°C, no differences were observed in absolute SkBF (H2O: 154 ± 44 PU; DEW: 152 ± 44 PU, p = 0.879), percent of maximal SkBF (H20: 60.6 ± 12.2%; DEW 62.4 ± 12.7% p = 0.272), absolute CVC (H2O: 2 ± 0.5 PU/mmHg; DEW: 1.5 ± 0.5 PU/mmHg, p = 0.368), or percent of maximal CVC (H2O): 63.8 ± 13.9%; DEW 62.6 ± 13.7% p = 0.787) in the DEW and H2O trials. However, during local heating at 39°C DEW did result in a higher MAP (H2O: 92 ± 7 mmHg; DEW: 100 ± 12 mmHg, p = 0.022) and heart rate (H2O: 56 ± 7 bpm; DEW 59 ± 8 bpm, p = 0.032) compared to H2O. Conclusion Under conditions of ischemia-reperfusion injury, these data indicate that, compared to an equivalent volume of water, consumption of 500 mL of a caffeinated soft drink sweetened with HFCS does not affect the cutaneous vasodilatory response to local heating, a mostly nitric oxide mediated response.

Independent and Cumulative Effects of Superoxide and iNOS on Cutaneous NO‐Dependent Vasodilation in Normotensive Non‐Hispanic Blacks and Whites

Cardiovascular disease is the foremost cause of morbidity and mortality in non-Hispanic Blacks (NHB). This may be due, in part, to reduced microvascular endothelial nitric oxide (NO) bioavailability and increased oxidative stress. The purpose of this study was to investigate the role of iNOS and superoxide, individually and cumulatively, in the cutaneous microvascular response to local heating in normotensive NHB and non-Hispanic Whites (NHW). Participants (n = 6 per group) were instrumented with four microdialysis fibers 1) lactated Ringer's solution (control), 2) 0.1 mM 1400W iNOS inhibitor, 3) 10 μM tempol, a superoxide dismutase mimetic to scavenge superoxide, and 4) combined 1400W + tempol. Following perfusate infusion, local skin temperature was increased via rapid local heating to 39°C (0.1°C s-1). Once skin blood flow plateaued, 20 mM L-NAME was infused to quantify endothelial NOS-dependent vasodilation to the local heating response. Following L-NAME infusion, the local heaters were increased to 43°C and 54mM of sodium nitroprusside was infused to elicit maximal cutaneous vasodilation. Skin blood flow was measured via laser-doppler flowmetry (LDF) throughout the local heating protocol. Percent NO contribution (%NO) was calculated as the difference between the local heating plateau and the post-L-NAME plateau multiplied by 100. Data are means ± SD. The %NO contribution was reduced at control sites in NHB relative to NHW (46 ± 5 vs. 62 ± 10 %NO, p = 0.03). Each experimental site was significantly different compared to control in NHB participants [(1400W, 63 ± 7 %NO, p = 0.01); (tempol, 61 ± 8 %NO, p = 0.01); (combined, 77 ± 9 %NO, p < 0.01)]. There was no effect of any of the treatments on %NO in NHW participants. Percent NO contribution at the combined site in NHB was significantly higher compared to control in NHW (p = 0.02). These data indicate combined superoxide scavenging and iNOS inhibition can increase endothelial NO-dependent cutaneous vasodilation more than either treatment alone in NHB.

Microvascular Vasodilatory Consequences of Acute Consumption of a High Fructose Caffeinated Soft Drink

PurposeExcessive intake of high fructose sugar sweetened beverages is associated with a greater risk of cardiovascular disease. This increased risk may be attributed, in part, to fructose‐mediated elevations in vasoconstrictor tone. Compared to water, consumption of a high fructose caffeinated soft drink elicits vasoconstriction in the kidneys and augments the renal vasoconstrictor response during sympathetic stimulation. It is unknown if these observed effects are specific to the kidneys or are indicative of a systemic vascular response. Endothelial dysfunction, which is characterized by a pro‐vasoconstrictor shift mostly due to reductions in nitric oxide bioavailability, is one of the earliest pathogenic vascular changes leading to cardiovascular disease. Experimental investigation of microvascular endothelial function may offer insight into the mechanisms contributing to the elevated cardiovascular disease risk associated with intake of high fructose sugar sweetened beverages. Therefore, the purpose of this study was to test the hypothesis that acute consumption of a high fructose caffeinated soft drink attenuates the cutaneous microvascular vasodilatory response to local heating, a primarily nitric oxide mediated response.MethodsIn a randomized cross‐over design, 8 healthy adults (26 ± 2 y, 4 women) consumed either 500 mL of a high‐fructose caffeinated beverage (Mountain Dew®, Soda) or 500 mL of water (H2O) while resting supine. Red blood cell flux, an index of skin blood flow, was measured at two sites on the dorsal aspect of the forearm using laser‐Doppler flowmetry probes seated in a local heater. Skin blood flow, blood pressure (finger photoplethysmography) and heart rate (ECG) were continuously measured. Data were analyzed at baseline, 30 min post‐consumption, and the last 5 min following 40 min of local heating at 39°C and 20 min of local heating at 44°C. Heating at 39°C was chosen because at this skin temperature and duration of heating the skin blood flow response is primarily nitric oxide dependent. Skin blood flow measures were averaged between sites and expressed as cutaneous vascular conductance (CVC), calculated as skin blood flow divided by mean arterial pressure. Data are presented as a percentage of the CVC response to local heating at 44°C (CVCmax).ResultsMean arterial pressure did not differ between Soda and H2O at any time‐point (P=0.82). Heart rate was higher in Soda during local heating to 44°C (56 ± 7 vs. 52 ± 8 bpm, P=0.04), but did not differ at any other time‐point (P≥0.35). CVCmax did not differ between the Soda (3.5 ± 1.2 PU/mmHg) and H2O (3.4 ± 0.5 PU/mmHg) trials (P=0.82). CVC 30 min post‐consumption (Soda: 9 ± 7, H2O: 13 ± 18% CVCmax, P=0.53) or during local heating at 39°C (Soda: 58 ± 17, H2O: 58 ± 18% CVCmax, P=0.91) were not different between Soda and H2O.ConclusionsThese preliminary findings suggest the cutaneous microvascular vasodilator response to local heating is not affected by acute consumption of high fructose caffeinated beverage. It is possible that the vasoconstrictor response following acute high fructose caffeinated soft drink consumption may be specific to the kidneys and that systemic changes may not occur.

Acute consumption of flavanol-rich cocoa beverage improves attenuated cutaneous microvascular function in healthy young African Americans

Flavanols have beneficial effects on vascular health and we have recently demonstrated that cerebral vasodilatory capacity in healthy young African Americans (AA) is improved with acute flavanol intake relative to aged-matched Caucasian Americans (CA). However, whether the positive benefits of acute flavanol consumption would also be present in the cutaneous microvascular circulation of AA remains unknown. Thus, we hypothesized that acute consumption of flavanol-rich cocoa (FC) would improve the previously reported reduced cutaneous microvascular responses to local heating in young AA. Seven AA and seven CA participated in this double-blind crossover study. Data were collected on two different days, separated by a minimum of one week. Two intradermal microdialysis membranes were inserted in the forearm and each site was randomly assigned to receive lactated Ringer's solution or NO synthase (NOS) inhibitor. Participants were randomly assigned to consume either a non-flavanol containing (NF) beverage or FC beverage. Cutaneous vascular conductance (CVC) was calculated as cutaneous blood flux/mean arterial pressure and normalized as % maximal CVC (%CVCmax). The difference in %CVCmax between the Ringer's site and NOS inhibited site was calculated to assess NO contribution (Δ %CVCmax). In the Ringer's site, acute consumption of FC beverage improved %CVCmax during 39 °C heating when compared to NF beverage in AA (NF: 36 ± 6 vs. FC: 47 ± 5%CVCmax; P < .01) while there was similar %CVCmax during 39 °C heating between beverages in CA (NF: 55 ± 4 vs. FC: 59 ± 5%CVCmax; P = .40). During 39 °C heating, NO contribution was significantly higher with FC beverage than NF beverage in AA (NF: 27 ± 5 vs. FC: 35 ± 4 Δ %CVCmax; P = .03) while there was similar NO contribution between beverages in CA (NF: 42 ± 4 vs. FC: 45 ± 4 Δ %CVCmax; P = .36). This data suggests that acute consumption of FC could be a therapeutic solution to improve an attenuated microvascular function in young AA.

Effect of iNOS on Cutaneous Thermal Hyperemia in Non‐Hispanic Blacks versus Non‐Hispanic Whites

Non‐Hispanic Blacks exhibit a blunted cutaneous microvascular response to local heating due, in part, to a decrease in nitric oxide (NO) bioavailability compared to non‐Hispanic Whites. Inducible NO synthase (iNOS) is known to contribute to vascular dysfunction; however, it is unknown whether iNOS contributes to microvascular dysfunction in NHB. The purpose of this study was to examine the role of iNOS on cutaneous microvascular function in NHB vs. NHW. Young, healthy non‐Hispanic Black and White participants (n = 4 per group) were instrumented with 2 microdialysis fibers for infusion of lactated Ringer's solution (control) and 0.1 mM 1400W (iNOS inhibitor), respectively. Following Ringer's and 1400W infusion, local skin temperature was increased via rapid local heating to 39°C at a rate of 0.1°C s−1. Once skin blood flow plateaued, 20 mM L‐NAME was infused to quantify endothelial NO synthase (eNOS)‐dependent vasodilation to the local heating response. Following L‐NAME infusion, the local heaters were increased to 43°C and 54mM of sodium nitroprusside was infused to elicit maximal endothelium‐independent cutaneous vasodilation. Skin blood flow was measured via laser‐doppler flowmetry (LDF) throughout the local heating protocol. Cutaneous vascular conductance (CVC) was calculated as LDF flow divided by mean arterial pressure and normalized to maximum (%CVCmax). iNOS inhibition minimally increased the initial peak in non‐Hispanic Blacks (33±6 vs. 41±8 %CVCmax) but had no effect in non‐Hispanic Whites (53±9 vs. 55±6 %CVCmax), suggesting an increased sensory nerve response in non‐Hispanic Blacks following blockade. Inhibition of iNOS (66±10 %CVCmax) did not alter microvascular function compared to control (70±14 %CVCmax) in non‐Hispanic Whites; however, microvascular function increased (47±11 vs. 60±10 %CVCmax) in non‐Hispanic Blacks, suggesting an increase in basal iNOS concentrations. Notably, iNOS inhibition in non‐Hispanic Blacks increased %CVCmax to a level similar to non‐Hispanic Whites. The %NO‐dependent vasodilation did not change in non‐Hispanic Whites with infusion of 1400W (60±5 vs. 61±5 %); however, infusion of 1400W increased the %NO‐dependent vasodilation in non‐Hispanic Blacks (44±6 vs. 57±3 %), suggesting increased levels of circulating iNOS impairs endothelial‐dependent vasodilation. These findings indicate iNOS‐derived NO contributes to reduced eNOS‐dependent microvascular vasodilation in young, healthy non‐Hispanic Blacks.Support or Funding InformationGrant Number: 1R01HL141205‐01This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

The effect of aging on vasomotion responses to varying rates of local heating.

We compared the cutaneous microvascular vasomotion responses of 8 young (23 ± 1 yr) and 8 older (68 ± 2 yr) adults in the forearm and leg using laser‐Doppler fluxmetry (LDF) and wavelet analysis to investigate endothelial, neurogenic, and myogenic activity. We measured cutaneous microvascular responses at uncontrolled basal temperature (27 ± 2.2 °C), controlled basal temperature (33 °C), and initial vasodilation (onset of heating), and sustained vasodilation, at 42 and 44 °C, in response to both a slow (0.1 °C · 10 s‐1) and a fast (0.5 °C · 10 s‐1) local heating protocol. At baseline (no heating), there were no differences between the groups (all P &gt; 0.05). At a controlled local temperature of 33 °C (thermoneutral), neurogenic activity was higher in the leg of the young compared to the older group (P = 0.04). Following the initiation of the heating protocols, the young participants responded with higher neurogenic activity in the forearm compared to the older group during fast local heating (P = 0.03), but not in response to slow local heating (P &gt; 0.05). In the leg, the young group had higher endothelial nitric oxideindependent activity compared to the older group (P = 0.01) for both heating protocols. The young group also had an increase in endothelial nitric oxide‐dependent activity during the slow protocol (P &lt; 0.001), while the older cohort experienced increases in neurogenic (P = 0.02) and myogenic (P = 0.04) activity. Following 35 min at 42 °C, neurogenic activity was significantly increased in the leg of the older group compared to the young group during the slow heating protocol (P = 0.02). Furthermore, after increasing local temperature from 42 to 44 °C, the older adults had higher endothelial nitric oxide‐independent activity (P = 0.04) in the forearm of the fast protocol while the young subjects had higher neurogenic activity (P = 0.04). Neurogenic activity in the leg of the older group was increased (P = 0.02) during the fast protocol at 44 °C. These results suggest that regional differences in the response to local heating persist with age and that the primary mechanisms responsible for vasodilation caused by local heating are diminished with age; however, overall vasodilation is offset by the other mechanisms. Moreover, our results suggest that as we age the reliance on endothelial activity shifts from endothelial nitric oxide‐dependent to endothelial nitric oxide‐independent mechanisms. These data suggest that the cutaneous bioavailability of nitric oxide is diminished with age.Support or Funding InformationBall State University SPA Fellows StipendThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

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.

Insulin Resistance Adversely Affects Cutaneous Microvascular Perfusion Responses to Insulin Iontophoresis in Spinal Cord Injury

Insulin is a vasoactive hormone and second messenger of nitric oxide that facilitates endothelial-mediated dilatation of the microvasculature with assistance by the sympathetic nervous system (SNS). The sensitivity or resistance of endothelial-mediated mechanisms that regulate skin blood flow may play an integral role in optimizing skin perfusion in vascular beds where SNS vasomotor impairment is present. Spinal cord injury (SCI) is characterized by interruption of supraspinal SNS control of sublesional vasomotor tone. PURPOSE: To determine the effects of insulin resistance (IR) on sublesional cutaneous perfusion responses to insulin provocation in persons with SCI. METHODS: A prospective, open-label, non-randomized, placebo-controlled investigation was performed in persons with SCI and an able-bodied (AB) cohort. These groups were subdivided based on fasting plasma insulin (FPI) concentration cut-offs for IR (≥13.13 mIU/ml) or insulin sensitive (IS: <13.13 mIU/ml) designations into four subgroups: ABIS (n=21); SCIS (n=21); ABIR (n=9); SCIR (n=11). Laser Doppler flowmetry characterized the peak blood perfusion unit (BPU) responses (percent change from baseline) to insulin or placebo iontophoresis in the lower extremities, and the corresponding BPU responses were log10 transformed to facilitate comparisons. The NetIns BPU response was calculated (Insulin-Placebo BPU responses) to provide the effect of insulin to that of the acetylcholine-mediated BPU response. RESULTS: The groups were matched for demographics. By study design, FPI was different between the IS and IR subgroups. In ABIS, the BPU responses to insulin were significantly greater than placebo (p<0.05 and p<0.0001, respectively). In ABIR and SCIR, insulin did not produce a BPU response that differed from placebo. In SCIS, the insulin BPU response was greater than placebo (p<0.0001). The NetIns response was significantly greater in both IS groups compared to their corresponding IR group. CONCLUSIONS: Persons with SCI have sublesional microvascular endothelial dysfunction. The presence of IR has a further confounding effect on endothelial-mediated changes to cutaneous perfusion and appears to be an important modifiable risk factor for the optimization of cutaneous perfusion in the lower extremities of persons with SCI.

Microvascular reactivity to thermal stimulation in patients with diabetes mellitus and polyneuropathy.

The study aimed to investigate local thermally induced microvascular reactivity in patients with type 1 (T1DM) or type 2 diabetes mellitus (T2DM) and polyneuropathy and to compare it with healthy controls. A hundred and fourteen subjects were investigated divided into 3 groups: 1st group -20 patients with T1DM; 2nd group -50 patients with T2DM; 3rd group -44 healthy controls. The skin perfusions of the first tiptoe were monitored by laser Doppler flowmetry during thermal test. The initial (PUi) and basal perfusions at 32°C (PUb) tended to be higher in the DM groups and the PUb of T1DM group was higher compared with the healthy subjects. The perfusion responses to heating were attenuated in the patients compared with the controls. The calculated vasodilator heat-induced indices were significantly lower and the vasoconstrictor indices during relative cooling in the recovery period were significantly higher in DM patients related to the healthy subjects. The reduced cutaneous microvascular responses to local thermal stimulation in the plantar sides of the toes of both T1DM and T2DM patients with polyneuropathy were similar to those found by previous studies in other investigated sites of glabrous and nonglabrous skin of patients with DM.

Assessment of microvascular endothelial function in type 1 diabetes using laser speckle contrast imaging

ObjectiveTo test whether laser speckle contrast imaging (LSCI) coupled with physiological post-occlusive reactive hyperemia (PORH) and pharmacological iontophoresis of acetylcholine (ACh) as local vasodilator stimuli could distinguish between cutaneous microvascular responses of Type 1 Diabetes (T1DM)’s patients with endothelial dysfunction and that of healthy controls. MethodsPatients with T1DM aged ≥12years completed a clinical-epidemiological questionnaire. Data detailing patients' such as daily insulin dose, duration of diabetes, and use of pharmaceuticals such as antihypertensive drugs and statins that could interfere with endothelial function were obtained. Vascular reactivity was assessed in the forearm by LSCI and PORH at baseline and during iontophoresis of ACh using increasing anodic currents of 30, 60, 90, 120, 150 and 180μA in 10second intervals. ResultsThis study included 50 patients with T1DM and 30 control subjects. The mean resting flux did not differ between patients and control subjects. T1DM patients exhibited endothelial dysfunction upon challenge with physiological or pharmacological stimuli. The microvascular response to both ACh and PORH (i.e., maximum response at peak and amplitude) were significantly reduced in patients with diabetes compared with control subjects (p<0.001). ConclusionWe demonstrated that endothelium-dependent skin microvascular vasodilator responses are significantly impaired in patients with T1DM compared to healthy subjects investigated using LSCI coupled with ACh iontophoresis and PORH. Additionally, we find that LSCI is a promising methodology for studying physiological vascular reactivity in T1DM.

Cutaneous microvascular responses to reactive hyperaemia and their relation to small arterial compliance in healthy males

Cutaneous microvascular responses to reactive hyperaemia and their relation to small arterial compliance in healthy males