Cutaneous Vasodilator Response Research Articles

Involvement of nitric oxide synthase and reactive oxygen species in TRPA1-mediated cutaneous vasodilation in young and older adults.

To investigate the nitric oxide synthase (NOS) and reactive oxygen species (ROS) contributions of the cutaneous vasodilator response to transient receptor potential ankyrin-1 channel (TRPA1) activation in young and older adults. In sixteen young (20±2years, 8 females) and sixteen older adults (61±5years, 8 females), cutaneous vascular conductance normalized to maximum vasodilation (%CVCmax) was assessed at four dorsal forearm skin sites continuously perfused via microdialysis with: 1) vehicle solution (Control, 2% dimethyl sulfoxide, 2% Ringer, 96% propylene glycol), 2) 10mM Ascorbate (non-specific ROS inhibitor), 3) 10mML-NAME (non-specific NOS inhibitor), or 4) Ascorbate+L-NAME. The TRPA1 agonist cinnamaldehyde was co-administered at all sites [0% (baseline), 2.9%, 8.8%, 26.4%; ≥ 30min per dose]. %CVCmax was not different between groups for Control, L-NAME, and Ascorbate (all p>0.05). However, there were significant main dose effects for each site wherein %CVCmax was greater than baseline from 2.9% to 26.4% cinnamaldehyde for Control and Ascorbate, and at 26.4% cinnamaldehyde for L-NAME and Ascorbate+L-NAME (all p<0.05). For Ascorbate+L-NAME, there was a significant main group effect, wherein perfusion was 6 %CVCmax [95% CI: 2, 11, p<0.05] greater in the older compared to the young group across all cinnamaldehyde doses. There was a significant main site effect for area under the curve wherein L-NAME and Ascorbate+L-NAME were lower than Control and Ascorbate across groups (all p<0.05). The NOS-dependent cutaneous vasodilator response to TRPA1 activation is maintained in older adults, with no detectable contribution of ascorbate-sensitive ROS in either age group.

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.

Estradiol Augments Sensory Nerve‐Mediated Vasodilation in Young Women

Local heating of the skin elicits biphasic vasodilation: a sensory nerve‐mediated initial peak (axon reflex) and an endothelial‐dependent plateau. We have previously shown that sex hormones, particularly estradiol (E2), improves cutaneous endothelial‐dependent vasodilation, but less is known about the effects of E2 on cutaneous sensory nerve‐mediated vasodilation.PURPOSEWe tested the hypothesis that E2 enhances sensory‐nerve mediated vasodilation in response to local heating of the skin in young women.METHODSWe retrospectively analyzed data in 15 healthy young women (age 24 ± 4 yr; MAP 84 ± 6 mmHg; BMI 24 ± 3 kg/m2). Endogenous sex hormone production was suppressed with daily administration of a gonadotropin‐releasing hormone antagonist (GnRHant; Ganirelix) for 10 days. E2 (0.1 mg/day, Vivelle‐Dot) was added back via transdermal patch on days 4–10. Cutaneous vasodilatory responses to local heating were measured on days 4 and 10 using laser Doppler flowmetry during microdialysis perfusions of lactated Ringer’s (control), and in a subset of women (n=6), L‐NAME (non‐selective nitric oxide synthase inhibition). Cutaneous vascular conductance (CVC) was calculated during the initial peak of the axon reflex during local heating (42°C) and normalized to maximal vasodilation achieved by perfusion of sodium nitroprusside (28mM) and heating to 43°C.RESULTSSensory nerve‐mediated vasodilation increased during E2 administration compared to GnRHant (E2: 71 ± 15, GnRHant: 57 ± 18 %CVCmax; p=0.046). Blockade of nitric oxide with L‐NAME did not blunt the axon reflex during GnRHant (control: 57 ± 18 vs. L‐NAME: 50 ± 17 %CVCmax; p=0.401) or E2 administration (control: 71 ± 15 vs. L‐NAME: 52 ± 19 %CVCmax; p=0.152).CONCLUSIONThese preliminary findings suggest that E2 enhances sensory nerve‐mediated vasodilation in young women, and that this may occur through mechanisms independent of nitric oxide. Future mechanistic studies isolating the nitric oxide component and other pathways could help elucidate the role of E2 in sensory nerve‐mediated vasodilation.

TRPA1 Channel Activation With Cinnamaldehyde Induces Cutaneous Vasodilation Through NOS, but Not COX and KCa Channel, Mechanisms in Humans.

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 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 4 dorsal forearm skin sites treated by intradermal microdialysis with (1) 1.985% dimethyl sulfoxide + 0.015% lactated Ringer solution with propylene glycol (vehicle control), (2) 10 mM l-NAME, a nonselective NOS inhibitor, (3) 10 mM ketorolac, a nonselective COX inhibitor, or (4) 50 mM tetraethylammonium, a nonselective 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 ≥30 minutes). 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%, and 80% 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.

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.

Abstract P276: A High Sodium Diet Reduces Cutaneous Microvascular Function In Normotensive Individuals With Salt Sensitive Blood Pressure

Impaired vascular function likely contributes to the association between dietary sodium intake and the development of cardiovascular disease. Using the cutaneous microvasculature as a model, we have previously shown that a high sodium (HS) diet blunts local heating-induced vasodilation in normotensive individuals with salt resistant (SR) blood pressure (BP). However, the effect of a HS diet on the cutaneous microvasculature in normotensive salt sensitive (SS) individuals remains unclear. Therefore, we tested the hypothesis that cutaneous microvascular function is reduced by a HS diet to a greater degree in SS compared to SR individuals. After each 7-day controlled feeding diet (low sodium (LS) = 20 mmol/day; HS = 300 mmol/day), an intradermal microdialysis fiber was inserted in the ventral forearm and perfused with Ringer’s solution. Skin blood flow (SkBF) was continuously monitored via laser Doppler flowmetry and a local heating unit was placed over the fiber and heated to 42°C until SkBF reached a stable plateau. Site-specific maximal SkBF was determined by perfusing 28mM sodium nitroprusside and heating to 43°C. Mean arterial pressure (MAP) was assessed at regular intervals on the contralateral arm and was used to calculate cutaneous vascular conductance (CVC = SkBF / MAP). Subjects wore a 24-hr ambulatory BP monitor and collected their urine on the final day of each diet. Fourteen subjects (9W / 5M, 42 ± 14 yr) whose MAP increased &gt;5 mmHg (Δ8 ± 1 mmHg) on the HS diet were defined as SS and were compared to 14 age- (43± 14 yr) and sex-matched SR subjects (Δ1 ± 3 mmHg). SS and SR had similar MAP at baseline (88 ± 9 vs. 90 ± 8 mmHg, P = 0.88) and urinary sodium excretion was increased similarly across groups by the HS diet (Δ239 ± 104 vs. Δ220 ± 66 mmol / 24 hr, P = 0.20). Cutaneous vasodilation in response to local heating was decreased on the HS diet relative to the LS diet in both SS (Δ-9 ± 9 %CVCmax, P = 0.005) and SR (Δ-9 ± 9 %CVCmax, P=0.005); however, there was not a group x diet interaction (P = 0.99). In contrast to our hypothesis, these results suggest that the deleterious effects of high sodium diets on cutaneous microvascular function are similar in normotensive salt sensitive and salt resistant individuals.

Effect of sensory blockade and rate of sensory stimulation on local heating induced axon reflex response in facial skin.

Local neuronal circuits in non-glabrous skin drive the initial increase of the biphasic cutaneous vasodilation response to fast non-noxious heating. Voltage-sensitive Na+ (NaV) channel inhibition blocks the afferent limb of the non-glabrous forearm cutaneous axon reflex. Slow local heating does not engage this response. These mechanisms have not been adequately investigated or extended into areas associated with flushing pathology. We hypothesized that despite regional differences in sensory afferents, both sensory blockade and slowing the heating rate would abate the cutaneous axon reflex-mediated vasodilator responses in facial skin. We measured skin blood flow responses (laser-Doppler flowmetry) of 6 healthy subjects (5 female) to non-noxious forearm, cheek, and forehead local heating, expressed as a percentage of cutaneous vascular conductance at plateau (CVC=flux/mean arterial pressure). We assessed CVC during fast (1°C/30s) and slow (1°C/10min) local heating to 43°C in both NaV inhibition (topical 2.5% lidocaine/prilocaine) and control conditions. NaV inhibition decreased forearm (control: 84±4, block: 34±9%plateau, p<0.001) and trended toward decreased forehead (control: 90±3, block: 68±3%plateau, p=0.057) initial CVC peaks but did not alter cheek responses (control: 90±3, block: 92±13%plateau, p=0.862) to fast heating. Slow heating eliminated the initial CVC peak incidence for all locations, and we observed similar results with combined slow heating and NaV inhibition. Slower sensory afferent activation rate eliminated the axon reflex response in facial and non-glabrous skin, but topical sensory blockade did not block axon reflex responses in flushing-prone cheek skin. Thus, slower heating protocols are needed to abate facial, particularly cheek, axon reflex responses.

Regional variation in nitric oxide-dependent cutaneous vasodilatation during local heating in young adults.

What is the central question of this study? Are regional differences in nitric oxide (NO)-dependent cutaneous vasodilatation during local skin heating present in young adults? What is the main finding and its importance? NO-dependent cutaneous vasodilatation varied across the body. The abdomen demonstrated larger NO contributions, while the chest demonstrated smaller NO contributions, compared to other regions. This exploratory work is an important first step in characterizing regional heterogeneity of cutaneous microvascular control across the torso and limbs. Equally, it serves to generate hypotheses for future studies examining regional cutaneous microvascular control in ageing and disease. Regional variations in cutaneous vasodilatation during local skin heating exist across the body. While nitric oxide (NO) is a well-known modulator of this response, the extent of regional differences in NO-dependent cutaneous vasodilatation during local skin heating remains uncertain. In 16 habitually active young adults (8 females; 25±5years), cutaneous vascular conductance, normalized to maximum vasodilatation (% CVCmax ), was assessed at the upper chest, abdomen, dorsal forearm, thigh and lateral calf during local skin heating. Across all regions, local skin temperatures were simultaneously increased from 33 to 42°C (1°Cper 10s), and held until a stable heating plateau was achieved (∼40min). Next, with local skin temperature maintained at 42°C, 20mM of NG -nitro-l-arginine methyl ester (l-NAME) was continuously infused at each site until a stable l-NAME plateau was achieved (∼40min). The difference between heating and l-NAME plateaus was identified as the NO contribution for each region. There was no evidence for region-specific responses at baseline (P=0.561), the heating plateau (P=0.351) or l-NAME plateau (P=0.082), but there was for the NO contribution (P=0.048). Overall, point estimates for between-region differences in the NO contribution varied across the body from 0 to 19% CVCmax . The greatest effects were observed for the abdomen, wherein the NO contribution was consistently greater than for the other regions (range: 9-19% CVCmax ). The chest was consistently lower than the other regions (range: 7-19% CVCmax ). The smallest effects were observed between limb regions (range: 0-2% CVCmax ). These findings advance our understanding of the mechanisms influencing regional variations in the cutaneous vasodilator response to local skin heating in young adults.

Delayed window of improvements in skin microvascular function following a single bout of remote ischaemic preconditioning.

What is the central question of this study? Animal infarct studies indicate a delayed window of cardiac protection after remote ischaemic preconditioning (RIPC); however, the presence and duration of this delayed effect have not been examined in human microvasculature in vivo. What is the main finding and its importance? Cutaneous vasodilatation induced by local heating or ACh was increased significantly 24 and 48h after a single bout of RIPC, respectively. Neither response persisted beyond ∼48h. Sodium nitroprusside-induced cutaneous vasodilatation was not altered. These findings reveal a delayed increase in microvascular endothelial function after a single bout of RIPC. Remote ischaemic preconditioning (RIPC) induces protective effects from ischaemia-reperfusion injury. In the myocardium and conduit vasculature, a single bout of RIPC confers delayed protection that begins 24h afterwards and lasts for 2-3days. However, the extent and the time line in which a single bout of RIPC affects the human microvasculature are unclear. We hypothesized that a single bout of RIPC results in a delayed increase in skin microvascular function. Sixteen healthy participants (age, 23±4years; seven males, nine females; MAP, 82±7mmHg) were recruited to measure cutaneous microvascular function immediately before a single bout of RIPC and 24, 48 and 72h and 1week after the bout. The RIPC consisted of four repetitions of 5min of arm blood flow occlusion interspersed by 5min reperfusion. Skin blood flow responses to local heating (local temperature of 42°C), ACh and sodium nitroprusside were measured by laser speckle contrast imaging and expressed as the cutaneous vascular conductance (CVC; in perfusion units per millimetre of mercury). Vasodilatation in response to local heating was increased 24 and 48h after RIPC (ΔCVC, 1.05±0.07 vs. 1.18±0.07 and 1.24±0.08PUmmHg-1 , pre- vs. 24 and 48h post-RIPC; P<0.05). Acetylcholine-induced cutaneous vasodilatation increased significantly 48h after RIPC (ΔCVC, 0.71±0.07vs. 0.93±0.12PUmmHg-1 , pre- vs. 48h post-RIPC; P<0.05) and returned to baseline thereafter. Sodium nitroprusside-mediated vasodilatation did not change. Thus, a single bout of RIPC elicited a delayed response in the microvasculature, resulting in an improvement in the endothelium-dependent cutaneous vasodilatory response that peaked ∼48h post-RIPC.

ET‐1 Receptor Function in Women of Different Reproductive Age but Similar Chronological Age

Endothelial dysfunction is a primary driver of hypertension and cardiovascular disease. Our lab has previously shown that endothelin-1 (ET-1), which contributes to endothelial dysfunction, is regulated by changes in ovarian hormones in premenopausal women (PRE). Additionally, while the ETB receptor mediates vasodilation in PRE, this effect is lost in postmenopausal women. However, the influence of reproductive aging, independent of chronological aging, on the function of the ETB receptor is unclear. Purpose The purpose of this study was to test the hypothesis that ETB-mediated vasodilation is progressively reduced with advancing reproductive age in women who are of similar chronological age. Methods We used the STRAW+10 staging criteria to classify women as PRE (n=4, 47±1 yrs, 26±1 kg/m2, 81±4 mmHg), early perimenopausal (PERI) (n=6, 49±1 yrs, 25±1 kg/m2, 79±3 mmHg), or late PERI (n=9, 49±1 yrs, 23±1 kg/m2, 81±3 mmHg). Cutaneous vasodilatory responses to local heating were measured using laser doppler flowmetry during microdialysis perfusions of lactated Ringer's (Control), ETB receptor blockade (BQ-788, 300nM), and ETA receptor blockade (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. One-way ANOVAs were used to compare vasodilatory responses between groups with Tukey post-hoc tests. Data are presented as mean±SEM. Results By design, women were of similar chronological age (P=0.25) but at different reproductive stages. PRE showed the greatest cutaneous vasodilation in response to local heating (PRE: 93±4; early PERI: 80±2; late PERI: 90±3 %CVC max, P<0.05 vs early PERI). However, there were no differences in vasodilatory responses during ETB receptor blockade (PRE: 85±11; early PERI: 87±4; late PERI: 94±1 %CVC max, P=0.38) or ETA receptor blockade (PRE: 81±2; early PERI: 90±1; late PERI: 88±5 %CVC max, P=0.27) between groups. Conclusions These preliminary data suggest that microvascular endothelial function is reduced in early PERI, independent of chronological aging. Additionally, these preliminary comparisons suggest ETB-mediated vasodilation may not differ between PRE, early PERI, and late PERI. Still, future studies should repeat these measurements and correlate findings with concurrent measurements of ovarian hormones.

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

Transient receptor potential (TRP) channels exist in various cells and tissues including nerves and vascular endothelium. TRP channels are implicated in the regulation of several sensory organs associated with pain, pressure, and temperature. While there exists a number of TRP channels, transient receptor potential vanilloid 1 (TRPV1) and 4 (TRPV4) channels in human skin have been shown to modulate cutaneous vasodilation (Fujii et al., 2019; Wong et. al., 2012). Transient receptor potential ankyrin 1 (TRPA1) subtype, which belongs to the TRP channel, is thought to be activated by cold and possibly warm/hot temperatures (Wang and Siemens, 2015). Recently, we showed that TRPA1 channel activation with cinnamaldehyde induced cutaneous vasodilation in humans (Fujii et al., 2020). However, the mechanisms underlying this response remains to be determined. A previous study using mouse ear showed that nitric oxide (NO) synthase (NOS), which is a meditator of endothelium-dependent vasodilation, can modulate the TRPA1 channel induced cutaneous vasodilation (Aubdool et al., 2016). However, it is unclear if this relationship exists in humans. Moreover, whether cyclooxygenase (COX) and Ca2+ activated K+ (KCa) channels, which are also established modulators of endothelium-dependent vasodilation, contribute to TRPA1 channel induced cutaneous vasodilation remains to be directly assessed in humans. Based on the above, we evaluated the hypothesis that NOS, COX, and KCa channels mediate the TRPA1 channel induced cutaneous vasodilation in humans. To assess our hypothesis, cutaneous vascular conductance (CVC) was assessed in 9 healthy young adults (29 ± 6 years, 4 women) at four dorsal forearm skin sites treated by intradermal microdialysis with either: 1) vehicle control (98 % propylene glycol + 0.015% lactated Ringer solution + 1.985 % dimethyl sulfoxide), 2)10 mM N(G)-Nitro-L-arginine methylester, 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% of cinnamaldehyde concentrations, each lasting at least 30min). Administration of ≥8.8 % cinnamaldehyde increased CVC from baseline at the vehicle control site (e.g., 27.4± 2.7 % increase in CVC, P<0.05). NOS inhibition attenuated the cinnamaldehyde induced-cutaneous vasodilation at 2.9, 8.8, 26 and 80% concentrations relative to the vehicle control site (all P<0.05). COX inhibition and KCa channel blockade did not attenuate the cinnamaldehyde induced-cutaneous vasodilation relative to the vehicle control site at all concentrations (all P>0.05). 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 negligible contributions of COX and KCa channels.

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.

Impact of Endothelin on Vascular Function in Hypertensive Postmenopausal Women

Endothelin-1 contributes to vascular dysfunction in hypertensive adults through the endothelin-A receptor (ETAR). However, our laboratory has recently shown an important role for the ETB receptor (ETBR) in regulating vascular function in women. We tested the hypothesis that hypertension is associated with a decline in ETBR function in postmenopausal women (PMW), and that this decline can be attenuated by anti-hypertensive medication. We recruited normotensive PMW (NT; n=9, age: 60±4 yrs, BMI: 25±5 kg/m2), hypertensive PMW naïve to therapy (HT; n=8, age: 59±5 yrs, BMI: 26±2 kg/m2), and medicated hypertensive PMW (MedHT; n=8, age: 63±6 yrs, BMI: 25±5 kg/m2). Blood pressure (BP) readings were taken on more than 1 visit to confirm BP category. We measured cutaneous vasodilatory responses to local heating via laser Doppler flowmetry during microdialysis perfusions of lactated Ringer's (Control) and ETBR blockade (BQ-788, 300nM). 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. A two-way ANOVA was performed to compare the impact of hypertensive status on vasodilatory responses to ETBR antagonists. Groups were well matched except for resting blood pressure. Systolic BP was lowest in NT compared to the HT and MedHT groups (NT:122±9, HT; 148±11, MedHT: 131±10 mmHg; P<0.02), but diastolic BP was similar between groups (NT: 68±5, HT: 76±7, MedHT: 73±8 mmHg, P=0.15). Plasma ET-1 was lower in NT compared to HT (NT: 1.29±0.24, HT: 1.83±0.2, MedHT: 1.57±0.44 pg/mL; P=0.03). Microvascular vasodilation (control site) was similar between groups (NT: 90±7, HT: 86±13, MedHT: 89±7 %CVCmax; P=0.56). Furthermore, ETBR blockade did not alter vasodilatory responses to local heating (NT: 90±7, HT: 91±9, MedHT: 84±11 %CVCmax, P=0.99). These preliminary data suggest that the ETBR does not contribute to vascular dysfunction in hypertensive PMW. Additional data are needed to understand the mechanisms contributing to hypertension in women.

The Impact of ET B Receptors on the Axon Reflex During Local Heating in Healthy Young Women

Endothelin-1 (ET-1) is a vasoconstrictor that acts on the vasculature through ETA and ETB receptors. Both ETA and ETB receptors are located in the skin and are involved in regulating skin blood flow. ETB receptors are also located on axon terminals on c-type nociceptor fibers. Rapid local heating stimulates the axon reflex which has been established as a mediator of the initial vasodilation response. Although ETA receptors have been shown to augment the axon reflex resulting in a vasodilation, less is known about the role of the ETB receptors on the axon reflex. Purpose The purpose of this study was to determine the contribution of ETB receptors to the axon reflex response. Methods We retrospectively analyzed data in 24 healthy young women (27±10 yrs). Cutaneous vasodilatory responses to local heating were measured using laser doppler flowmetry during microdialysis perfusions of lactated Ringer's (control) and ETB receptor blockade (BQ-788, 300nM). Cutaneous vascular conductance (CVC) was calculated during the initial peak and nadir of the axon reflex during local heating (42°C), and normalized to maximal vasodilation achieved by perfusion of sodium nitroprusside (28mM) and heating to 43°C. We used paired samples t-tests to analyze differences in vasodilation between control and ETB receptor blockade sites. Results All subjects were normotensive (MAP: 83±8 mmHg) and had a normal BMI (23±3 kg/m2). There were no significant differences in skin blood flow between control and ETB receptor blockade sites during initial peak (control: 63 ±15; ETB receptor blockade: 62±17 %CVC max, P=0.70) or nadir (control: 52±16; ETB receptor blockade: 50±18 %CVC max, P=0.49). There was also no significant difference between conditions in time to initial peak (control: 142±75; ETB receptor blockade: 140±53 s, P=0.79). Conclusions These preliminary findings suggest ETB receptors do not impact axon reflex mediated vasodilation during local heating in healthy young women. Future research is needed to understand the mechanisms contributing to the axon reflex to regulate blood flow in the cutaneous circulation.

Regional cutaneous vasodilator responses to rapid and gradual local heating in young adults.

To examine the extent of regional variations in cutaneous vasodilatation during rapid and gradual local thermal hyperaemia (LTH) in young adults. In thirty young adults (21±3 years, 15 females), cutaneous vascular conductance, normalized to maximum local skin heating at 44°C (%CVCmax), was assessed at the upper chest, abdomen, dorsal arm, dorsal forearm, thigh, and medial calf during rapid (33-42°C at 1°C·20 s-1) and gradual (33-42°C at 1°C·5 min-1) LTH on separate days. For both protocols, local temperatures were held at 42°C for up to 35min, followed by 20-30min at 44°C. During rapid LTH, between-region responses were evaluated at baseline, the initial vasodilator peak, and 42°C plateau. During gradual LTH, responses were assessed at baseline and the 42°C plateau. There were significant main effects of body region on %CVCmax for the initial peak and plateau during rapid LTH and for the plateau during gradual LTH (all P<0.001) Conversely, main effects of sex and the sex by region interaction were not significant (all P>0.05). The magnitudes of between-region differences varied across the body (~1-17% range). The greatest effects were observed for the abdomen, wherein responses were consistently lower compared to other regions. Further, responses were consistent between males and females across all body regions and heating phases. Regional variations in the cutaneous vasodilator response to local heating are evident for rapid and gradual LTH in young adults, with the largest effects observed for the abdomen, albeit regional differences were similar between sexes.

KCa channels are major contributors to ATP-induced cutaneous vasodilation in healthy older adults

ObjectiveTo examine the contributions of calcium-activated K+ (KCa) channels and nitric oxide synthase (NOS) to adenosine triphosphate (ATP)-induced cutaneous vasodilation in healthy older adults. MethodsIn eleven older adults (69 ± 2 years, 5 females), cutaneous vascular conductance, normalized to maximum vasodilation (%CVCmax) was assessed at four dorsal forearm skin sites that were continuously perfused with either 1) lactated Ringer solution (Control), 2) 50 mM tetraethylammonium (TEA, KCa channel blocker), 3) 10 mM Nω-nitro-L-arginine (L-NNA, NOS inhibitor), or 4) combined 50 mM TEA +10 mM L-NNA, via microdialysis. Local skin temperature was fixed at 33 °C at all sites with local heaters throughout the protocol while the cutaneous vasodilator response was assessed during coadministration of ATP (0.03, 0.3, 3, 30, 300 mM; 20 min per dose), followed by 50 mM sodium nitroprusside and local skin heating to 43 °C to achieve maximum vasodilation (20–30 min). ResultsBlockade of KCa channels blunted %CVCmax relative to Control from 0.3 to 300 mM ATP (All P < 0.05). A similar response was observed for the combined KCa channel blockade and NOS inhibition site from 3 to 300 mM ATP (All P < 0.05). Conversely, NOS inhibition alone did not influence %CVCmax across all ATP doses (All P > 0.05). ConclusionIn healthy older adults, KCa channels play an important role in modulating ATP-induced cutaneous vasodilation, while the NOS contribution to this response is negligible.

Ageing augments β-adrenergic cutaneous vasodilatation differently in men and women, with no effect on β-adrenergic sweating.

What is the central question of this study? β-Adrenergic receptor activation modulates cutaneous vasodilatation and sweating in young adults. In this study, we assessed whether age-related differences in β-adrenergic regulation of these responses exist and whether they differ between men and women. What is the main finding and its importance? We showed that ageing augmented β-adrenergic cutaneous vasodilatation, although the pattern of response differed between men and women. Ageing had no effect on β-adrenergic sweating in men or women. Our findings advance our understanding of age-related changes in the regulation of cutaneous vasodilatation and sweating and provide new directions for research on the significance of enhanced β-adrenergic cutaneous vasodilatation in older adults. β-Adrenergic receptor agonists, such as isoprenaline, can induce cutaneous vasodilatation and sweating in young adults. Given that cutaneous vasodilatation and sweating responses to whole-body heating and to pharmacological agonists, such as acetylcholine, ATP and nicotine, can differ in older adults, we assessed whether ageing also modulates β-adrenergic cutaneous vasodilatation and sweating and whether responses differ between men and women. In the context of the latter, prior reports showed that the effects of ageing on cutaneous vasodilatation (evoked with ATP and nicotine) and sweating (stimulated by acetylcholine) were sex dependent. Thus, in the present study, we assessed the role of β-adrenergic receptor activation on forearm cutaneous vasodilatation and sweating in 11 young men (24±4 years of age), 11 young women (23±5years of age), 11 older men (61±8years of age) and 11 older women (60±8years of age). Initially, a high dose (100µm) of isoprenaline was administered via intradermal microdialysis for 5min to induce maximal β-adrenergic sweating. Approximately 60min after the washout period, three incremental doses of isoprenaline were administered (1, 10 and 100µm, each for 25min) to assess dose-dependent cutaneous vasodilatation. Isoprenaline-mediated cutaneous vasodilatation was greater in both older men and older women relative to their young counterparts. Augmented cutaneous vasodilatory responses were observed at 1 and 10µm in women and at 100µm in men. Isoprenaline-mediated sweating was unaffected by ageing, regardless of sex. We show that ageing augments β-adrenergic cutaneous vasodilatation differently in men and women, without influencing β-adrenergic sweating.

ET B Receptor Responses In Young Women With A Family History Of Hypertension

Endothelin-1 (ET-1) contributes to endothelial dysfunction, a primary driver of hypertension and cardiovascular disease. Young women with a family history of hypertension (+FH), a group at risk for developing hypertension, display elevated resting plasma ET-1. Our lab has previously shown that in healthy young women, the ETB receptor mediates vasodilation. However, the function of ETB receptors has yet to be determined in young women +FH. PURPOSE: The purpose of this study was to test the hypothesis that +FH young women display attenuated ETB-mediated vasodilation. METHODS: Eight young women without a family history of hypertension (-FH; 23±2 yrs, 24±1 kg/m2) and 8 women +FH (23±2 yrs, 22±1 kg/m2) completed the study. Family history status was self-reported on a medical history questionnaire. Cutaneous vasodilatory responses to local heating were measured using laser doppler flowmetry during microdialysis perfusions of lactated Ringer’s (Control) and ETB receptor blockade (BQ-788, 300nM). 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. A two-way ANOVA was performed to compare the impact of familial history of hypertension on vasodilatory responses. Threshold for significance was set a priori at P<0.05. Data are presented as mean ± SEM. RESULTS: Resting mean arterial pressure (-FH: 80±3 vs. +FH: 85±2 mmHg, P=0.25) and plasma ET-1 (-FH, n=5: 1.2±0.2 vs. +FH, n=6: 1.5±0.2 pg/mL, P=0.43) were similar between groups. There was a trend for a significant group x time interaction for cutaneous vasodilatory responses (Drug: P=0.33, Group: P=0.63, Interaction: P=0.09); vasodilatory responses to Control tended to be lower in +FH (-FH: 95±1 vs. +FH: 89±4 %CVC max). Furthermore, blockade of ETB receptors tended to reduce vasodilation in -FH (Control: 95±1 vs. 87±3 %CVC max) but not +FH (Control: 89±4 vs. 91±2 %CVC max). CONCLUSION: These preliminary data suggest that in young, otherwise healthy women, ETB receptor function may be altered based on hypertensive family history status; however additional data are needed. Furthermore, data in +FH young men are needed given the known sex differences in the ET-1 system. Supported by: NIH R01 HL 146558, P20 GM 113125.

Sex-differences in cholinergic, nicotinic, and β-adrenergic cutaneous vasodilation: Roles of nitric oxide synthase, cyclooxygenase, and K+ channels

Previous studies indicate that sex-related differences exist in the regulation of cutaneous vasodilation, however, the mechanisms remain unresolved. We assessed if sex-differences in young adults exist for cholinergic, nicotinic, and β-adrenergic cutaneous vasodilation with a focus on nitric oxide synthase (NOS), cyclooxygenase (COX), and K+ channel mechanisms. In twelve young men and thirteen young women, four intradermal forearm skin sites were perfused with the following: 1) lactated Ringer's solution (control), 2) 10 mM Nω-nitro-l-arginine, a non-selective NOS inhibitor, 3) 10 mM ketorolac, a non-selective COX inhibitor, or 4) 50 mM BaCl2, a nonspecific K+ channel blocker. At all four sites, cutaneous vasodilation was induced by 1) 10 mM nicotine, a nicotinic receptor agonist, 2) 100 μM isoproterenol, a nonselective β-adrenergic receptor agonist, and 3) 2 mM and 2000 mM acetylcholine, an acetylcholine receptor agonist. Nicotine and isoproterenol were administered for 3 min, whereas each acetylcholine dose was administered for 25 min. Regardless of treatment site, cutaneous vasodilation in response to nicotine and a high dose of acetylcholine (2000 mM) were lower in women than men. By contrast, isoproterenol induced cutaneous vasodilation was greater in women vs. men. Irrespective of sex, NOS inhibition or K+ channel blockade attenuated isoproterenol-mediated cutaneous vasodilation, whereas K+ channel blockade decreased nicotine-induced cutaneous vasodilation. Taken together, our findings indicate that while the mechanisms underlying cutaneous vasodilation are comparable between young men and women, sex-related differences in the magnitude of cutaneous vasodilation do exist and this response differs as a function of the receptor agonist.

ET‐1 Receptor Function in Women with Advancing Reproductive Age

Endothelin‐1 (ET‐1) contributes to endothelial dysfunction, a primary driver of hypertension and cardiovascular disease. Our lab has previously shown that the ETB receptor mediates vasodilation in premenopausal women (PRE), but this effect is lost in postmenopausal women (POST). Noticeable declines in endothelial function are evident early in the menopausal transition, but the function of the ETB receptor in perimenopausal women (PERI) is unclear.PURPOSEThe purpose of this study was to test the hypothesis that ETB‐mediated vasodilation progressively declines with advancing reproductive age in women.METHODSWe used the STRAW+10 staging criteria to classify women as PRE (n=12, 26±2 yrs, 23±1 kg/m2, 83±2 mmHg), PERI (n=9, 50±1 yrs, 24±1 kg/m2, 84±3 mmHg), or POST (n=11, 56±1 yrs, 24±1 kg/m2, 87±2 mmHg). Cutaneous vasodilatory responses to local heating were measured using laser doppler flowmetry during microdialysis perfusions of lactated Ringer’s (Control), ETB receptor blockade (BQ‐788, 300nM), and ETA receptor blockade (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.RESULTSPRE showed the greatest cutaneous vasodilation in response to local heating (PRE: 93±2; PERI: 84±2; POST: 88±2 %CVC max, P&lt;0.05 vs PERI and POST). There was a trend for increased vasodilatory responses to ETB receptor blockade with advancing reproductive age (PRE: 85±3; PERI: 91±2; POST: 92±3 %CVC max, P=0.13). However, there were no differences in vasodilatory responses during ETA receptor blockade (PRE: 90±2; PERI: 91±3; POST: 92±3 %CVC max, P=0.84). Finally, brachial artery flow‐mediated dilation tended to decline (PRE: 7±1; PERI: 6±1; POST: 5±1 %Δ, P=0.09) while pulse wave velocity increased with advancing reproductive age (PRE: 6±0; PERI: 7±0; POST: 7±0 m/s, P&lt;0.05 vs PERI and POST).CONCLUSIONSThese preliminary data suggest that adverse changes in vascular function, and potentially ETB receptor function, are evident early in PERI. Therefore, future research examining the role of the ET‐1 pathway in progressive vascular dysfunction throughout the menopausal transition is warranted.Support or Funding InformationNIH R01 HL 146558, P20 GM 113125